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This is the circuit of a simple 12 volt battery charger for Lead Acid battery. It gives 12 volt and 5 Amps current for quick charging of the battery. If the battery is partially discharged, full charge will be attained in one hour. The circuit uses a 0-14 volt 5 Ampere Step down transformer and a 10 Amps Bridge rectifier module to convert AC to DC. Since pulsed DC is good for Lead Acid battery, a low value smoothing capacitor is used as C1.To monitor the charging status, Ampere meter is provided in the positive rail. LED act as the Charger on status.

Schematic of the Simple 12 Volt Battery Charger Circuit. Hi Riyagote, yes it will work, Lm3i7 safe working voltage is 35v, to avoid over heating and safe operation of the ckt i prefer the in put voltage supplied to the ic is limited to a max of 22 volts. With your 18v center tapped transformer you will get around25.4v.what you can do is give the 25.4v to the collector of a 2n3055 npn transistor and connect a 7818 reg ic in put point to the collector of 2n 3055 tr and ground the centre pin of the ic in series with 5 nos of IN4007 diodes, anode of the diode should go to the ic pin and the cathode of the last diode should go to the gnd ie negative, (you can also put a 3v zener ) but putting the IN4007 diodes are more reliable. Now connect the out put pin of the ic to the base of the 2n3055 tr and connect the emitter of the transistor to the input of the charger ckt now your in put voltage will be 20.4v.provide heat sink for the transistor. V.Sambath kumar.

There were not very many diagrams. I’m looking for a diagram of a Linwood MP8 battery charger. The wiring on it was like a rat’s nest and it used 3 amp diodes which were running at their limit. The circuit allegedly produces 6 or 12 volts by operating a switch. Another switch gave High or Low output. Its this last bit which is puzzling as I’m not sure whether “Low” was achieved by putting the extra diode in series with the output or by going from full-wave to half-wave. When I took it to pieces it all seemed so simple but its not!

BU-408: Charging Nickel-metal-hydride Know how to apply the correct charge to moderate heat and prevent overcharge. The charge algorithm for NiMH is similar to NiCd with the exception that NiMH is more complex. Negative Delta V to detect full charge is faint, especially when charging at less than 0.5C. A mismatched or hot pack reduces the symptoms further.

NDV in a NiMH charger should respond to a voltage drop of 5mV per cell or less. This requires electronic filtering to compensate for noise and voltage fluctuations induced by the battery and the charger. Well-designed NiMH chargers include NDV, voltage plateau, delta temperature (dT/dt), temperature threshold and time-out timers into the full-charge detection algorithm.

These “or-gates” utilize whatever comes first. Many chargers include a 30-minute topping charge of 0.1C to boost the capacity by a few percentage points.

Some advanced chargers apply an initial fast charge of 1C. When reaching a certain voltage threshold, a rest of a few minutes is added, allowing the battery to cool down. The charge continues at a lower current and then applies further current reductions as the charge progresses. This scheme continues until the battery is fully charged.

Known as the “step-differential charge,” this method works well for all nickel-based batteries. Chargers utilizing the step-differential or other aggressive charge methods achieve a capacity gain of about 6 percent over a more basic charger. Although a higher capacity is desirable, filling the battery to the brim adds stress and shortens the overall battery life. Rather than achieving the expected 350–400 service cycles, the aggressive charger might exhaust the pack after 300 cycles. NiMH dislikes overcharge, and the trickle charge is set to around 0.05C. NiCd is better at absorbing overcharge and the original NiCd chargers had a trickle charge of 0.1C.

The differences in trickle charge current and the need for more sensitive full-charge detection render the original NiCd charger unsuitable for NiMH batteries. A NiMH in a NiCd charger would overheat, but a NiCd in a NiMH charger functions well. Modern chargers accommodate both battery systems.

It is difficult, if not impossible, to slow charge a NiMH battery. At a C rate of 0.1C to 0.3C, the voltage and temperature profiles do not exhibit defined characteristics to trigger full-charge detection, and the charger must depend on a timer.

Harmful overcharge can occur when charging partially or fully charged batteries, even if the battery remains cold. The same scenario occurs if the battery has lost capacity and can only hold half the charge. In essence, this battery has shrunk to half the size while the fixed timer is programmed to apply a 100 percent charge without regard for battery condition. Many battery users complain about shorter than expected service life and the fault might lie in the charger. Low-priced consumer chargers are prone to incorrect charging.

If you want to improve battery performance with a low-cost charger, estimate the battery state-of-charge and set the charge time accordingly. Remove the batteries when presumed full. If your charger charges at a high charge rate, do a temperature check. Lukewarm indicates that the batteries may be full. It is better to remove the batteries early and recharge before each use than to leave them in the charger for eventual use.

Simple Guidelines for Charging Nickel-based Batteries • The charge efficiency of nickel-based is close to 100 percent up to 70 percent charge. The pack remains cool but it begins to warm up with decreased efficiency towards full charge. • Nickel-based batteries must cool down on trickle charge.

If warm, trickle charge is too high. • Consumer chargers do not always terminate the charge correctly. Remove the batteries when warm to the touch. Discontinue using a charger that “cooks” batteries. • Charge at room temperature. Do not charge when hot or at freezing temperatures.

(See ) • Nickel-based batteries are best fast charged; a lingering slow charge causes “.” • Nickel- and lithium-based batteries require different charge algorithms. A NiMH charger can also charge NiCd; a NiCd charger would overcharge NiMH. • Do not leave a nickel-based battery in the charger for more than a few days. If possible, remove the packs and apply a brief charge before use.

Last updated 2016-05-17 *** Please Read Regarding Comments *** Comments are intended for 'commenting,' an open discussion amongst site visitors. Battery University monitors the comments and understands the importance of expressing perspectives and opinions in a shared forum. However, all communication must be done with the use of appropriate language and the avoidance of spam and discrimination. If you have a suggestion or would like to report an error, please use the ' form or email us at:. We like to hear from you but we cannot answer all inquiries. We recommend posting your question in the comment sections for the Battery University Group (BUG) to share. Dear Isidor, I have a question regarding household appliances with NiMH batteries.

I own a 18V Black and Decker pv1825n Dustbuster. I found the batterypack details here: The factory charger is 7.2-24V voltage converter (85mA).

Charge time is around 21hours. The manual recommends leaving the machine connected to the charger when not in use. I am not sure that would be the correct way to improve lifespan. Regularly, I use the machine every two to three day for a few minutes. From what i have learned off your site i guess the following would be better: charge for 24h, disconnect from charger, use regularly untill I notice capacity starts to drop, charge again for 24h etc. Additionalym a deep discharge every three to four months is a recommended. What would be your opinion in the case?

I find that a lot of appliances come with batteries and instructions that i cannot match well with the information on your site. My compliments on an excellent website! It has helped me on many occasions and I have made myself an expert in the eyes of family and friends with battery problems (there are many) just by relaying the information i found here. I am the battery engineer from one of the leading rechargeable battery company Firstly,the charge time is 21hours is not reasonable, it is too long time, when the battery is fully discharged,you must to wait too long for the sencond discharge Secondly,When the machine not in use for long time such one day or longer, you’d better disconnenct the charger, it will be better for the battery cyclelife. As you know overcharge will be a waste of electricity and will short the battery use life. Many household appliances supplier worry about that the user can not fully charge the battery which leading to the short run time and complaint.due to the self-discharge of ni-mh battery, in fact, the self-discharge in a short time such as one day or two days is neglectful, and long time overcharge with trickle will be bad for the battery life So i agree your method to charge and discharge the battery welcome to discuss this issue. I work on a government base where rules are strickly followed concerning safety.

My NiMH batteries for my e-bike are in 15 lb packs of sealed f-cells. (by design 24v, run in series) Do NiMH batteries give off any gasses while charging? What hazzards exist when charging the batteries? (Such as fire, leaking, (I know that Lead acid batteries do and my boss is wanting to wrap me into the same category, leaving me to prove that the NiMH batteries are safe. I need manufacturer documentation to prove this, but my batteries are generic.

ON a seperate note, if I charge my batteries in a refrigerator to reduce their heat during charging, I notice that they charge faster. I also notice if I charge them to full then reset the charger after a eight hour full charge that my batteries get an extra 1-3V overall. (normally I am at 57 and if I reset I get upwards of 59.5 after another hour and a half of charging.) Am I hurting the batteries using either process? There is a safety venting in the battery cap, which will open to give off gasses to release the battery inner pressure when the battery is deep over charged,so, do not deep over charge the battery to long time,it will lead to leaking even fire or explode the charge efficiency is related to the temperature, the higher temperature the lower charge efficiency, so, you can charge the battery faster in the refrigerator to reduce their heat during charging. We advise not to reset the charger when the battery is fully charged to prevent from deep over charged.

I have a 20mA constant current source charging a 9V 180 mAHr NiMh battery with a microprocessor A/D that measures the terminal voltage. When the terminal voltage reaches 9.0 software shuts off the charger.

The time to reach 9.0 volts from a pretty much discharged state is about an hour so my hunch is that the battery is no where near fully charged but the terminal voltage really never increases much past that level. Can the can the state of charge be determined from terminal voltage alone? I’ve seen tables on flooded lead-acid batteries that relate voltage to percent of charge, but never on NiMh. Is there such a thing? The statement that NICd chargers aren’t good for Ni-MH cells does not take into account the four-fold increase in cell capacity that took place over the time period where Cadmium cells were displaced by metal hydride cells.

Consumer trickle-chargers for NiCd batteries do not adjust themselves for the capacity of the cell. Python Programming For The Absolute Beginner Free Pdf. The old trickle chargers I had for 600mAH NiCd cells might not be well suited for 600mAH Ni-MH cells, but AA cells in Ni-MH are now 2,000 to 3,000 mAH, so the fast trickle charger that pumped 0.2C/h into a 600mAH NiCd cell is now a slow trickle 0.05C/hr charger, even though the 120mA current flow has not changed. I still use my 1980s vintage NiCd chargers with good (but not optimum) results - VooDude.

Jim wrote: “I have a 20mA constant current source charging a 9V 180 mAHr NiMh battery with a microprocessor A/D that measures the terminal voltage. When the terminal voltage reaches 9.0 software shuts off the charger. The time to reach 9.0 volts from a pretty much discharged state is about an hour so my hunch is that the battery is no where near fully charged but the terminal voltage really never increases much past that level.” Jim you don’t have a (nominal) 9V NiMH battery, as the nominal voltage will be a multiple of 1.2.

So you have a NiMH in the form factor of a 9V (PP3) battery, but the actual nominal voltage will most likely be either 7.2 volts or 8.4 volts. To determine the correct final voltage it’s important that you know the number of cells (nominal voltage). If it’s not marked on the battery then measure the open circuit voltage of the battery when it’s getting close to (but not quite) discharged, and see if it’s closer to 7.2 or to 8.4.

My 8.4V 180mA (9 volt PP3 replacements) reach a final voltage of around 10 volts at a 0.1C (18mA) charge rate. A final voltage setting of 9V will be too low for an 8.4V nominal NiMH to charge more than about 20% maximum. Also be aware that the “correct” final voltage will change with temperature as well as with battery age/condition, so it’s best to have a time limit to the charge as well. Hi, NiMH batteries are new for me and I want to find some tips for charging and preserving them,I announce you that I have 4 AA batteries Energizer of 2500 mAh and 4 Sanyo 2700 mAh normal (not LSD) and 4-channel smart charger that charge all batteries fully discharged in 3 hours: 1.

Keeping the battery empty for a week or longer is damaging it? If the battery is at 70% of capacity and I begin charging, is this damaging it? How to prevent self discharge as much as possible 4.

What is the best use on low temperatures (sometimes if I am outside and is cold my camera wont want even to start and if I come inside the batteries restores and the camera is working; is there a way to make the camera work at that low temperatures (0 C) not fully charged? The charge cycle of NiMh is the same as charge cycle of Li-Ion (0% to 100% or 2 times 50% to 100% etc.)? Hi I have 4 nimh AA batteries of 2500mah (use for my camera) and those have a problem: until last week I charge them with a smart charger that have only 2 chanels.with -deltaV protection, hight temperature protection.and timer protection. Recently I bought a smarter charger with 4 chanels and damaged battery protection, and it sems that 3 batteries are damaged (and this charger don’t charge them). How can I restore them (I know that is posible with an analyzer but I don’t afford one) thank you! That cell is cheap low quality Chinese or Turkish (brand C.F.L.) cell that certainly doesn’t have 900 mAh. My MP3 player that draws about 90-110 mA only runs for about 1h45m on that cell, but it doesn’t fully discharge it.

After it shuts down saying that the battery is flat, the cell still has about 1.18V when loaded with 5 ohm resistor. I never bothered to measure the capacity accurately (I’d have to use a stopwatch for that because I don’t have battery analyzer), but it’s safe to say that it is half of the rated value, so 35 mA is reasonable current. Sorry I forgot to mention all this in first post. The “charger” is a simple wall plug with open circuit voltage of about 6V and a resistor to limit the current.

I terminate the charge when I estimate that the battery is full. I also charge two or three cells in series on this charger with a lower resistor value. I’ve read several articles on recharging NiMH and they all say that slow charge at about 0.1C (or 0.05C) is OK, but none of those articles mention the voltage.

Can these cells be damaged by overvoltage even if the current is kept low and what is the maximum safe voltage for NiMH cell? Should the slow charge be terminated when voltage reaches certain point? I am working on a school project involving charging 4-AAA NiMH batteries, 1.2V each, with a small solar panel used for outside lighting. The solar panel being used is a 12V 40mA solar panel. There are restrcitions on the size of the solar panel that can be used.

The batteries are charging in series. Would it be better to use a solar panel that had a lower voltage rating and higher current rating, even if the to total output power of the solar panel is less. I was thinking that an incease in current would cause the batteries to charge faster. “VooDude: The statement that NICd chargers aren’t good for Ni-MH cells does not take into account the four-fold increase in cell capacity that took place over the time period where Cadmium cells were displaced by metal hydride cells.” Is there any comment on this? I have a NiCd-era ‘overnight charger’ for 4xAA cells, which cranks out whopping 50 mA current.

It takes some 2+ days to charge modern high capacity cells. Is there any harm in using such a slow charger, even if the charger is forgotten on for a few days?

How about Eneloop cells - are they more sensitive? I have an 8 AA cell battery pack in my RC transmitter that I want to charge with my multifunction “icharger 208B” battery charger. The more I read you excellent website, the more I realize how little I know about batteries and how dangerous my limited knowledge can be. 4 of the cells in the pack are 2100mAh Ni-MH 1.2V and 4 of the cells are 2000mAh Ni-MH 1.2V I can set the current limit only on my icharger 208B charger.

So, my questions regarding my battery pack: 1: What amperage current limit should I be charging this cell pack? 2: Should I discharge before charging? 3: As I do not know a thing about C ratings of values, can you please give me the answer in amps or milliamps and tell me if and how this amps answer relates to a C number, if at all? 4: What voltage should I expect to see the auto cutoff? You would better charge your ni-mh AA2000mah and 2100mah from 200mah to 400mah 2.,do not need to dicharge the cells if your charger have the max voltage control ability 3. About the C rate, it means the charge current/ the capacity of the cell.

If your charge the ni-mh AA2000mah 1.2V cell at 400mah current, then,the charge C rate is 400mah/2000mah=0.2C. For better life performance, I advise the charge rate is 0.1C to 0.2C,and the charge time is 12h to 6h 4.I advise the max voltage should control at 1.45V for each cell. Can you comment on what to look for/check in a batch of unknown cells, and which cells are worth keeping and which should just be recycled? Tenergy right now is closing out old-dtyle NiMH cells (light blue wrapper, lower case “e” on the label). I’ve bought several dozen from different closeout places hoping they’re ok. Most of them arrive showing about 1.0 volt. Those seem so far to recharge OK (except on a Maha charger, which shows “HIGH” for every single one, and won’t charge them).

Others arrive showing 0.4-0.5v and won’t hold charge more than a day or two; some of those get very hot. >Do you mean how to check it is Ni-mh or ni-cd?? I described them by brand name and appearance above. >in my opinion, the cells’ voltage should be more than 1.2V I agree, if they were new stock I'd expect that. These are half price. I’m asking about a particular cell widely available right now in closeout/discount sales, half price.

Conclusion—some seem OK, but batches are probably not worth buying, from my experience so far. >How can you accept the cells showing 0.4V-0.5V? I complained and got some money back on one batch, apparently the closeout place knew they were a mixed lot —but the replacements are in the 1.0v range. I’m asking if these cells that arrive showing 1.0v are worth trying to put into regular use. So far, they seem to hold charge for at least a week or so—checking with a ZTS tester. The ones that showed half a volt before charging will charge up, and work OK for a few hours’ use in a LED flashlight _if_ used immediately after charging; but lose their charge within a day or so.

I’d guess Tenergy dumped old or poorly stored cells cheap: Again: light blue wrapper, lower case “e” on the label, NiMH. These aren’t currently shown on Tenergy’s website, apparently discontinued.

Hi, I have a 8.4V 1200mAH 7 cell airsoft battery. I recently tuned my gun and tested it out with this battery. The gun fired rapidly at first then the rate of fire gradually dropped until it came to a stop.

I measured the voltage with a multimeter and got around 9.28V. I wonder if that means my battery is fully charged, half way or in need of a charge in order to run my airsoft gun. Please let me know, since if my battery is good, I would need to open up the gearbox and spend hours retuning my gun.

I am trying to figure out a way for charging 3 batteries in a 4 battery charger, or 1 battery in a 2 battery charger. The only thing i was able to think was to construct a dumb battery consisting of two diodes in series. They should be connected to conduct current, and as the total forward voltage drop is 1.4 volts, the charger will shut off when the actual battery voltage reaches 1.4 volts, as the total voltage is 2.8 volts. I have not tried it yet, and I would be very obliged if you could tell me your opinion about it.

I wonder also if I could do the same thing with a zener diode. I you can think of something better please let me know. Why not set the each charger channel for each cell independence?? Or, the charger have to test the volagage from the charger, take 2battery charger for example: if the charger test the voltage is above 1.6V from the channel when the cell(cells) put into. Then the charger know 2cells in the charger, and it can control the max voltage is 2.8V, if the charger test the voltage is less than 1.6V from the channel when the cell(cells) put into.

Then the charger know 2cells in the charger, and it can control the max voltage is 1.4Vbut there is a problem, if there is a bad cell is 0V, the charger can not judge 1or 2 cells in the charger. The battery chargers I am talking about are not intelligent chargers. For this reason they cannot figure out from the battery voltage if one or two batteries are charging. Actually if you connect one battery it will not charge it at all because the batteries are connected internally in series, so it will pass no current at all. So I have to replace one battery with a circuit that will make the charger believe that there are 2 batteries connected. The idea is that the charger will continue to charge the 1 battery (in series with the dumb battery) till the total voltage across them reaches 2.8 volts, and then it will cut off the current. (the voltage drop across the series connected forward biased diodes will be in the vicinity of 1.4 volts, so that the remaining 1.4 volts will be at the terminals of the actual battery when it will be fully charged).

P.S I accidentally pushed the “stop receiving notifications for this comment” button, so please reset it if possible. Dear Edward, My son has a Xootr powered scooter, with a 24volt NiMh 3200 maH battery pack inside.

He bought it without a charger, but it came fully charged, so we know it works. I have purchased 2 different NiMh chargers, but they will not recharge the pack. I think it must be due to the temp. Sensor that both these intelligent chargers use. Can you describe how the connection between the pack and the charger works? I believe the charger refuses to charge until it sees some sort of signal or conductivity from the sensor wire. Neither charger comes with any instruction as to how to connect this third conductor!

Thanks very much! I have owned for 5.5 years a 1999 Ford Ranger electric vehicle that uses 39 x 8V NiMH Panasonic batteries (312 V nominal).

The charger is built into the vehicle. Ford instructs to leave vehicle on the charger when not driving (in part, for battery temperature control (I live in MA)). I bought the vehicle at with about 8K miles, now has 26K miles. Each winter, the “miles available” is less than summer (Nernst equation, for sure), but this year the reduction is greater. Also, the battery behaves as expected for the first quarter-charge, but falls off rapidly as soon as it goes below 75% charge (I’ve heard that this happens to some batteries). What problem(s) does this suggest? (I spoke to a local battery distributor franchisee who says he can test the performance of the individual 8V batteries if I bring it to him, but that requires removal of the one-ton pack, so I’m looking for information before doing so.) Thanks!

Edward, what is your view about frequent “topping-up” with nimh (AA) with regard to cycles the battery can do? My thought is, with the battery loosing about 10-30% first day out of the charger In theory, one could apply say.2c for an hour every day (or shorter if it hits NDV termination) and give it back 20% daily. So, a non-LSD can stay fresh every day. I have read that shallow cycle with Li-ion works well without burning up the cycles. This article further suggest the math is charging merely 20% will burn up 20% of a cycle. So, a 100 full-cycle is the same as 500 20% top up cycle.

In your opinion, do you think the math is similar with Nimh? Thanks, Edward. That is informative. I am thinking about converting my old battery killing dumb charger into a timed battery refresher. Had partial re-charge use up a cycle as a deep discharge/recharge, I would drop the idea of cooking up a time-based refresher.

Speaking of old As I get older, my memory gets worst but my old NiCd’s memory keep on getting stronger. If only I am more like a NiCd battery, I could remember that Never mind, I forgot what I could remember. Thanks again for the info, Mr. I am attempting to power a small circuit drawing around 100mA max with 6, 3100mA non protected li-ion batteries in series providing 22.2v. The batteries are to be connected to a 6 cell pcm (protection circuit board) through which the circuit will draw the supply. The PCM board can be adjusted for max discharge current.

What would be the ideal maximum discharge current I should set the pcm to then? 0.1C or 0.05C? (roughly 310mA & 155mA respectively) Is there any significant advantage of setting it at 0.1C over 0.05C?

I am trying to charge 1600mAh ni-mh 9.6 v battery with a simple solar cell and have a few questions: 1. At first we were worried about the battery exploding. Is this a possibility given the low current provided?

Do I charge the battery with 9.6v or 1.2v since that is the charge on each cell? Given the low current, it will be difficult to determine when it is done charging. It does not need to fully charge each time for this application.

At such a low current, how would you advise detecting when it is full enough? We have not picked out the solar cell yet, but it needs to be cheap. 24 hours to charge the battery would be fine since it will not be fully discharged each time. Do you have any recommendations on voltage and current to get?

Thank you for your help. Andrew, I am not a battery expert but battery “informed”. Until someone with better knowledge comes along, here is what I can suggest: ——- Q1.

At first we were worried about the battery exploding. Is this a possibility given the low current provided?

Since you are talking NiMh, it is unlikely it explodes particularly with such low current. Do I charge the battery with 9.6v or 1.2v since that is the charge on each cell?

Since you said this is 9.6v, I assume you are accessing it as a pack (of 8 cells in series) rather than each of the 8 individual cells. When you are accessing it as a pack, you charge it as 9.6v.

However, If you are breaking the pack up (physically, or merely connecting to each cell individually), then you charge it at the cell voltage as 1.2v. Either way, your charging voltage needs to be higher than the pack/cell voltage. For a 1.2v cell, 1.8v-2.8v works nicely. For 9.6v, I use just a bit over 11’ish to 13v works nicely. I can pump 1C into my 11volt battery at 13volt.

(1C is to charge 1-watt-hour battery in 1 hour.) At lower current, you don’t need as high a voltage (wastes less). You can look at it this way: Current is what got stored, but Voltage is what pushes it in.

If you spend all your energy pushing, very little energy is left after you got in. So, if you set your 1watt panel output to twice the voltage needed, you get only 1/2 the current to be stored. Of course, the battery is not 100% efficient in converting the power into chemical energy for storing. You push in 100maH, the battery probably stores about 2/3 or 3/4 of that. Given the low current, it will be difficult to determine when it is done charging. It does not need to fully charge each time for this application. At such a low current, how would you advise detecting when it is full enough?

NiMh termination is typically based on NDV (negative delta voltage) of about 5mV. You need pretty good circuitry to detect 5mV out of 1.2. DT/dt or dV/dt are other methods. All those require fairly complex electronic. So, you either use your solar panel to power a consumer-charger wasting energy converting, or you do estimation. If your battery is say about 8 good AA cell, you will be talking about 16-20 WH (watt-hour) of power.

If your solar panel is 1Watt, it will take you 16-20 hours to charge it full. You can estimate based on that. Not picked out the solar cell yet, but it needs to be cheap. 24 hours to Do you have any recommendations on voltage and current to get? To charge 9.6v, a 12-13volt source should work nicely. Volt multiplied by Current is your Watts.

So, 12Watt panel will give you 1A at 12volt. The wattage you need depends on your battery size. You need at least 1/10. If your battery is 8 AA batteries as in my example in Q3-answer, 16 to 20 watt-hour storage needs around 1.6 to 2 watt-hours (if you have 10 hours of sun where you live). Much below 0.8w (1/20 of 16), you may not have enough current to even make a dent. You are loosing all the energy in the transfer, conversion, etc. And nothing to store.

So, to charge at 1/10 for 10 hours but you have only 5 hours of sun, you need to double the panel’s wattage. If you want it to be cheap, ahem, you are looking at the wrong solution.

To charge and discharge daily, you will likely spend many times over on the panel and batteries than say a good recharge battery with high capacity and high cycle – say one with enough power that you charge once a month with a normal AC plug in charger. I use a few solar sidewalk lights on my lawn.

Each year I need to replace my battery because of over-discharge and rough environment outdoor. Money-wise, I am better off using regular AC recharge with but for the trouble of charging or changing battery. I am actually considering converting it to AC charge with an all day-trickle (1/20C). With AC recharge, I wont have to clean the darn solar panels on those lights anymore.

Such a pain – after a few weeks, they are clouded and the lawn dust (pollen, grass bits). If I don’t clean it every month, the batteries are undercharged even in the summer and so it over-discharge every night. Even with regular cleaning, a few days of no-sun send the batteries into over-discharge (and thus convert itself to garbage a bit at a time and killing itself in less than a year.). For new batteries my Maha MH-C9000 charger advices the “break in” charging function with 0.1C. So I started this process with a set of brandnew Eneloop XX.

To my surprise, the batteries (which were presumably almost fully charged) first received a charge that is more than their full capacity, given me the idea of heavily overcharging. On the other hand, the tension of 1.49V is not too high (at this moment the 900 mAh batteries received 1050 mAh and still charging).

Can anyone explain why the charger choses for this behaviour? Thanks, Herman. Edward: I am hoping you might be able to help me out I am trying to create a solar-powered bicyce light using NiMH batteries. My problem is, though I’m learning, is how this all fits together!

I am trying to create this light with an optimal combination of: - small physical size - easily recharged (solar) - long run times - ultra bright lights I have found a solar cell for battery charging that seems to be middle ground in terms of Volts (5V), Amps (40mAh) & physical size (58mm x 39mm), which works well with my design. Batteries are an area where I could really use your help. I was all ready to settle on NiMH, until I found Low Discharge NiMHand then the new LiFePo4 batteries.

My design concept is to keep this as small as possible. Physically, there is room for any combination up to 3 AA batteries, but as batteries will likely be the greatest expense, using one or two, or using a less expensive type of battery, would be best. So, here are a bunch of questions I hope you might be able to answer and shed some light! What do you think about Low Discharge NiMH? Not everyone uses their bike every day, so it would be great if the batteries wouldn’t drain out because of non use. Or should I look at a high-capacity NiMH? NiMH batteries usually say 1000 charge cycles.

But what happens if the solar charger is constantly cycling on and off trying to top off the battery? It would be nice to get 1000 days, or nearly 3 years out of the batterybut I’m concerned that every day use might impact the number of charge cycles. Also, I assume there needs to be some controls in place to not overcharge the batteries?

Can I use a solar charger to charge a Lithium Iron (LiFePo4)? I don’t know what the appropriate mAh should be, given that I am trying to keep this light as small, bright and powerful as possible—so I know there will have to be a tradeoff somewhere. I am planning to use two LEDs that will draw a total of 40mA.

So, any help you can offer would be greatly appreciated! Thanks, Rob Decker rdecker@x-media.com. Hello Ed, glad I found this site. My kids go thru AA batteries like crazy and I have been buying energizer nimh and others that have capacity from 2300 to 2650mah. Over time, the batteries stop charging on a 15 minute charger so I built my own microprocessor based charger with computer interface for secondary control and logging. It seems that if I deep cycle the batteries a few times the will start charging n the 15 minute chargers.

Some have lower voltage (less than 1v) when charged and again, deep discharge followed by rapid charge seems to heal them. The questions I have are around charging algorithms as I’ve been using 2.4amps which is approximately 1c.

This sounds high by your standards so I might ( with your confirmation) cut back to.5c. What I notice though, is most batteries heat up with a dT/dt greater than 1 degree per minute at even.5c and they are nowhere near charged. These are all the same brand with varying dT/dt. Are these batteries shot?

Also, at.5c, it seems like people chart better NDV drops than 5mv per cell. So what is the best NDV per cell at.5C and 1C? My charge software currently looks for 10mc NDV with a max temp of 140F and plan to add dT/dt as well but again, my experience is most batteries will exceed our 1 degree per minute even after stabilizing at 5 minute precharge.

One other question: for nimh batteries in the 2400mah range, what would you consider is a good stabilizing precharge at.5c time? The precharge gives the battery time to stabilize both temperature and voltage. I am using constant current obviously.

I’ve thought about using pulse charge at either.5c or 1c with a lesser duty cycle in my precharge as well. Any thoughts on this? I know this is asking a lot, but is there an ideal algorithm out there for nimh batteries in this capacity charged as single cells? Thanks, you articles are very informative!

I’ll reply to Jacques but Edward would be more professional: Jacques, If you use constant voltage with current limiting, and the current limit is held to no more than.1C, then you will be safe charging the batteries and will reach 100% capacity. You should use a temperature monitor as well just to be safe. This all assumes that you run your charging circuit so that the current limit is held at all times. If the current limiting circuit is not activated, then you will be running in constant voltage mode and this is not safe on the high end, and wont allow the batteries to reach full potential on the low end (of charge current).

Also, circuits to limit charge to.1C are very easy to build using an LM317 regulator with a current sense resistor in series with the load, tied back to the common. The LM317 will maintain 1.25V from output to common, using this voltage of 1.25 divided by.1c, you can set the sense (and current limit) resistor to any practical charge current up to 3A, assuming the lm350 is used instead of a 317, or up to 1.5A for the 317.

So I wouldn’t rely on a current limiting circuit from a power supply when you consider you can build a better charging circuit for less than $5USD. Some curent limiting power supplies work very effectively as a charger, again assuming the current limit is variable or known to be maintained at less than.1C. If the current limit is higher, you can use a timer to limit the charge time but this is risky and must be used with a temperature probe. I need advise or help. Please Ed or anybody with experience! I have Imax B6 charger and 2S 5000 mAh Lipo battery. When I set charger by instructions )Lipo-2S-7,2V-5000mAh cutoff-360 min cutoff, max 8,4V-5A charging or less 2A, 3A) it usually says “conection break”, or it starts to charge and It says “full” but each cell is at 3,5V.

Weather I charge it or balance charge it doesen’t charge more than 3,5 V per cell. Battery is brand new it is first charge after discharging in RC car. Car is set to cutoff at 3.0V, but it won’t go after I have driven it for 10 min. Dave, Your statement has no foundation with testing I have done and I assume Edward and others will agree.

Also, how do you determine initial charge or automatic switch off at full charge? It can’t be done without draining the battery. I have yet to see a reliable way to measure battery charge or capacity.

It can’t be done with voltage alone. You have to measure the voltage drop over time and this varies so greatly by battery it is completely unreliable. I have charts and data that demonstrate without a doubt that fast charging at.5C brings a battery up to full charge more reliably and efficiently than slow charge. I have a number of graphs the show the convergence of dTdt with NDV and find it to be extremely reliable.

Also, by using dTdt, I can detect a rise in termperature much more reliably than slow charging. My charger usually kicks off below 85 degrees F, which is consistently lower than most slow chargers on a timer. Heat is what impacts battery life. If you put a 80% charged battery on a 15 hour slow charger you will most likely exceed 85 degrees or as much as 100 degrees. The charger I built has all all the normal safeguards like dTdt, NDV, timers, max capacity, initial voltage, max voltage, etc, etc. It drops to.05c at full charge or can be set to do a.1C for an extra 30 or 60 minutes to top the battery off. I have found Edward’s advice on this site to be beyond reproach for the practical and efficient charging of both NIMH and NICD batteries, Jerry.

Hello, i am trying to charge 12v 800mAH(1.2v*10cells AA) NimH battery. I am charging it with an lm317 as a constant current source. Throughout the charging process the same current of 200mA(0.25C) is giving.charging start/stop and discharging start/stop is controlled by PIC. So it never goes beyond the predetermined value. My question is that during charging the battery voltage goes from 15 to 17.3v and so temperature. What might be the maximum voltage at this charging current and rate. And also which will be the better charge termination, a maximum threshold voltage or time.

I don’t want to make my charger complex by making it an intelligent charger. I am also ready to compromise the charging rate because the charging time can be as long as 8 hrs. Thanks Nikhil. Nikhil, I assume you aren’t using a temperature probe so you are limited in what you can do with a smart charger anyway.

Also, at that charge rate it is somewhat dangerous to charge batteries as they can overheat and cause a fire. I have done it myself and I am very knowledgeable about battery charging. Since you don’t have a temperature probe, the only thing you can do is set the maximum time to 6 hours using 1.5C total charge at.25C. Maximum charge voltage would be 24v though many chargers are much more conservative. The maximum charge voltage of 2v per cell would be considered an emergency type shutoff only, not an indicator of a fully charged battery pack. Another approach that would reduce the efficiency of your charger would be to charge for 10 minutes and then stop, let the battery pack voltage settle for one minute, and then measure the voltage.

If the voltage meets or exceeds 1.41V (some recommend as high as 1.46v) then the pack is charged. If the voltage is lower than 1.41v continue with another charge cycle. I suggest you add a thermistor to your charger at a minimum. If you do that, please come back and post as there would be other simple alternative ways to more accurately detect a peak charge and improve the efficiency of your charger. Hi Jerry, Thanks for your reply.

” the only thing you can do is set the maximum time to 6 hours using 1.5C total charge at.25C. “, sorry i can’t understand this statement. Did you mean starts charging at 1.5C and reduces the rate to 0.25C at the end? Is it’s safer to charge at 1.5C(1.2A) which is much higher than 0.25C.My circuit never charges a fully charged or partially charged battery. It only charges a discharged battery, that’s why i choose constant time charging and avoid thermistor. Also what might be the minimum discharge voltage for a 12v NIMH battery(load around 70 mA)?

Thanks and regards Nikhil. I found a nice 14.4 volt Makita drill that someone threw away. It has a 2.6 Ah NiMh battery. But it has no charger.

A new charger is very $$$, and the money would be better spent on a a new drill - UNLESS I can use a power supply to charge it. I have access to literally hundreds of power supplies at work. For example, I just found a small 15v, 1.33 amp power supply, but it’s a switching power supply.

Can I use this, provided I don’t leave the battery unattended? If not, what would be the proper rating for a P/S to charge this battery? ( I realized that you do NOT recommend PS chargers for nickel based, but it’s eithr that or toss it.) many thanks. Nikhil, What I meant was that at.25C charge rate the recommended charge time would be 6 hours.

Again, I would recommend a charge rate of.1C to avoid overheating and a potential fire if you have the time available. Then the recommended charge time would be 15 hours. I was referring to the standard total charge of 1.5 times capacity for batteries, not that you charge at that rate. Again, thermistors are inexpensive and the PIC chip has A2D converter making them easy to sense temperature. You are not charging at a high enough rate for a smart charger to detect peak on NiMH, but you can improve the efficiency and safety by using a temperature testing circuit.

Tom,, Every battery pack is different but I think it is safe to say a 15v power supply will not be high enough to charge a 14.4v battery. Most likely that battery is bad and was the source of the failure. Also, for NiCD and NiMH you need current limiting. It is a simple circuit using an LM350 or LM317 and a resistor. You not only need to exceed the voltage of the battery pack by a factor, you also then have to take into consideration the voltage drop of the charge circuit and cables, which would be generally in the 1.2 to 1.5v range. So I would think a starting point of 18-20v would be about right for a 14.4v pack, but again, it depends on so many factors not the least of which is the age and condition of the battery cells.

Also, if you have a shorted cell in the pack, the voltage required will be lower which is wrong but hard to detect with unknown batteries. Lastly, if you attach an unlimited current supply to the battery that has a low charge, it will easily exceed the 1.33A of your 15v supply. Look around your shop for a variable supply in the 24v range that also has current limiting. A secondary approach, on the cheap, would be to try the 15v supply with an amp meter inline to check the current. Keep the current under.26A and charge for 15 hours the first time. If the cells do not keep 14.4v once the charger is removed, then you most likely have a bad cell. Many 14.4v batteries exceed 17v when initially charged.

My apologies to Ed as I have no intent to hijack his board. I just love charging batteries and found the science, some of which is explained very well on this site, fascinating.

Something with my OCD must kick-in when I see an uncharged battery. Yes the author is definitely getting mixed up with SI and SI derived quantities and units then. Or they have made up their own confusing quantities using SI / SI-derived symbols eg “fast charge of 1C” reads to me fast charge of 1 coulomb which could be an Amp for a second, 10 Amps for a tenth of a second. C isn’t capacity of a battery, C is Capacitance (ability of an entity to store Charge), two very different quantities. Q or q is the symbol used for charge 1 mAh is 3.6C [1 coulomb is an Ampere Second A.s or As, coulomb ampere and second are all SI base units therefore an ampere hour = 3600C] I is used as the symbol for Current not C. It’s mAh not mah. Maurie, You should use the supplied charger which is a slow charger I believe not unlike those for my HT’s.

Generally, without a sophisticated circuit (which would be easy for you to design/build or replicate based on you being an amateur operator) it is best to charge each battery at a constant rate of.1C, C being the capacity of the battery contrary to Frank E above. So a constant current of 150mA for the 1500mA and 220mA for the 2200mA would give you the recommended charge rate of.1C. Most of the supplied wall wart chargers don’t do a really good job of current regulation for constant current and usually don’t provide the full.1C rate at first as that might require a higher voltage than it can supply. It is easy to wire a constant current source using an LM350 regulator. A fixed supply greater than 1.8x the battery voltage would do it as a source to the constant current circuit. Please note you should limit the charge time to 15 hours for.1C rates and also check the temperature occasionally.

C is generally used as it relates to batteries as being the Capacity in mAh’s, or milliamp hours. In case Frank is still policing this site, please note I used the correct case for the ‘A’ in milliamp hours. Also, Frank, please note I can’t read this fine print so I might not have the correct number of ‘L’s in the term milliamp.

Lastly, Frank, just to clarify, the character ‘C’ is used for more than just capacitance and is generally used for battery capacity. Look around and you will find it across the IEEE docs as well. I will apologize for incorrectly not capitalizing the ‘A’ in mAh in my rush to answer Frank’s question. At the risk of offending Edward, who’s kindly provides answers on this site for the benefit of all, (and I would understand if he bans me) I would like to point out to Frank that the character ‘*’ is often used for the term A-shole, Moron is usually capitalized and sometimes Idiot. My wife capitalizes ‘Butthead’ but I think these are all capitalized as those terms are proper nouns. I also would like to think people have more than enough to do then ask questions when they clearly don’t want or need an answer, *.

Hello, Magnus. Generally, the charge current is supplied by an external analog constant current source that is controlled by a microprocessor, either on or off at a minimum, though with extra circuitry, the constant current can be varied.

While charging under constant current load, the voltage is monitored continuously by a microprocessor ADC in most cases to be able to detect a 5mv or less drop per cell after either analog or algorithmic smoothing. To be clear, yes, the voltage is monitored while the charge current is applied. Please note that this is only one way to terminate a charge. I have found that delta Voltage is not quite as accurate as delta Temperature, and for Frank’s information, I capitalized the V and T to highlight the difference, and maybe to annoy him as well. Lastly, the charger should have maximum temperature and charge voltage limit safeguards as well as a fail-safe timer.

Batteries catch fire. They should be taken very seriously while charging at anything higher than.1C. Please refer to my earlier notes on the correct use of the character ‘C’ as it relates to charge rate. All in fun, Jerry, with only the best regards for Eduard.

Many thanks for your quick response and further comments. I’m planning to make an integrated charger using a BQ2002/F chip. It can sense a drop of 2.5 mV after peaking, and uses averaging of several voltage measurements. But I think I’ll also need to add some analog smoothing to the signal as the charging current will be a bit rough from the step-down inductor. Your comment about dT being more accurate than PVD is useful because BQ2002 only measures absolute temp and not rate of temp. Maybe I’ll look for a controller with this extra feature. Or I could write my own software, but it would be nice to get something ‘out of the box’.

Regards, Magnus. Magnus, I wrote my own software using an arduino board as there was a touch screen graphics ‘shield’ with Ethernet and SD card that I found useful to integrate.

Granted it is overkill for a battery charger, I wanted all the flexibility to do it once and last forever. Delta T takes a little more logic to detect, but the charts I made lead me to believe it is safer and more accurate than delta V for NiMH batteries. I highly recommend you take the approach of using your own microcontroller but it is more involved. Alan, I assume you can’t charge the three cells making the 3.6v pack individually? I dont think there is high enough voltage at the USB port (without regenerating it higher) to charge a 3.6v pack. Many of my NiMH single cells require 1.8v or higher for initial charge putting the absolute minimal requirement at 6v assuming a marginal voltage drop across the lm317 as well.

If you have a variable power supply, attach it to the battery with an ammeter inline as you increase the voltage to draw.05 times the capacity of the battery. The voltage read at that point plus.6v, better plus 1.2v, will be the minimal amount needed.

Using.6 volts will require you to build a transistor based constant current source opposed to the lm317. This is an excellent site—I have learned a lot from reading it all. I am still a little bit confused about my NiMH packs: I have a smart charger but it doesn’t have a temp probe. I have a 4.8V 2000MAh powering the radio in my RC boat. I run the model once a month or so.

I’m never really sure what percentage of the battery may have been used. If I’m charging it at C/20 (100mA), Is it OK to leave it charging for 24 hours? Another RC boat is powered by 6 cell 7.2 V NiMH packs. One is 3700MAh, the other is 5000MAh. My peak detecting charger has rates of 1, 2, and 4 amps. I’ve been charging them at the 1 amp setting—but maybe I should be using a higher setting?

Hello Bill, I will reply while waiting for Eduard. 1) Use any reliable thermometer against the pack after 24 hours to ensure the temperature doesn’t rise above 100 degrees F and you will be ok. I question whether you are getting a full charge and I also believe you might be doing long term damage to the battery by charging at a trickle rate of 1/20. My experience is that long term low current charging (below 1/15) might degrade battery performance. Rihanna Man Down Download Mp3 Free. If possible, I suggest you setup to charge at.1C for 14 hours. As an aside, excuse me while I point out to Frank that the capital ‘C’ to designate Capacity was used correctly by both of us.

2) I suggest you charge batteries at that same rate as they are drained in most if not all cases. Never exceed the manufacturers specifications if.

1) Use any reliable thermometer against the pack after 24 hours to ensure the temperature doesn’t rise above 100 degrees F and you will be ok. I question whether you are getting a full charge and I also believe you might be doing long term damage to the battery by charging at a trickle rate of 1/20. My experience is that long term low current charging (below 1/15) might degrade battery performance. If possible, I suggest you setup to charge at.1C for 14 hours. As an aside, excuse me while I point out to Frank that the capital ‘C’ to designate Capacity was used correctly by both of us. 2) I suggest you charge batteries at that same rate as they are drained in most if not all cases.

Never exceed the manufacturers specifications if listed. The only time I would charge at a higher rate than 1A is when time mattered. Higher charge rates increase temperature which is detrimental in most cases. Larry, Your scanner most likely came with a NiCD battery and the charger is probably just a 300ma power supply. I’ll bet the charge circuitry, if any, is in the scanner. Actually the charge circuitry could be as simple as a resistor to drop the current to something like 160ma which is the recommended rate for a 1600mah battery when peak detection, temperature and other safeguards aren’t supplied. If you can fit a 2100mah battery in there, and it looks like you can since you are inquiring about AA batteries, I don’t see any reason to not use it.

The charge circuitry in the scanner will still only supply the 160ma assuming it is limited to the supplied battery, so actually it will take longer to charge the new battery, something like 20 hours but you will have longer service life once charged. I buy the rechargeable batteries you commonly find in electronics stores made by Duracel. They are up to 2650mah capacity now and many times come with an inexpensive charger that works OK. I don’t think they do all the fancy programmable charge detection algorithms you can find for more money, but they get the job done efficiently. I would stay away from the 15 minute rechargeables, they never lasted for me as the charge rate was too high for the quality of the battery and typically they went thermal for me using their cheap charger. There are a number of very good programmable chargers out there, maybe Ed can recommend his favorite, I built my own after playing around with others for many years.

I have stated in earlier posts that I have found the delta temperature / delta time charge detection to be more reliable with better peak capacity than the delta voltage type. In any case, make sure you get a charger that has temperature sensing. I would expect to pay around $60 or less for a decent charger and many could be had for less than $45. Good luck Jerry.

Ed My team and I are handling a research on rechargeable wireless sensor. We using six Sanyo HR-3UTGA 1.2V 1,900mAh batteries, while dividing them into 2 parallels with 3 batteries per parallel to power up the sensor. These sensors are then charge using two Solar Cell 5V 50mA (0.25W) connected in serial. The problem we found is that some of the batteries (maybe few out of 6) will died off no matter we charge it under hot sun, indoor, or air-conditional room. Voltage of affected batteries will lies between 0.01V - 0.04V. These batteries still can be recharge until 1.4V, however, there will be higher chance for these batteries to break down again in future deployment.

Any suggestion for us to tackle the problem stated above? Are we overchaging the batteries and is there any solution to prevent it? Thank in advance. Hello Edward, I have a few questions regarding both NiMH batteries and NiCd batteries and chargers. I am not sure if you are familiar with the Sony ICR-100 and ICR-120 radios, but they are vintage radios, (from the mid to late 1960’s).

I have one of each radio and they both have their original chargers, however I suspect the ICR-120 charger is not working properly. Basically, I have been reading as much information as I can find about the radios and battery replacements. I have read that both radios used a set of two NiCd batteries spot-welded together, (each battery is supposed to be about 1.2 volts, 60mAh).

I found that I can replace the old ones for NiMH batteries giving me lots of improvements over the old NiCd’s like capacity, no “memory” effect, etc. Anyway, I have on order both a set of NiMH batteries and NiCd batteries. If I use the NiMH batteries, what sort of power output does the charger need to have, (both ideally and as a min-max for proper recharging), (these batteries will be connected together in series for a total of 2.4 volts and about 40mAh). If I used the NiCd batteries what sort of power does a charger need to put out for these? I am attempting to keep the radio sets are close to original configuration as possible.

They both came with their original storage cases, earphones, wall chargers and leather carrying case. The other question I have was related to the original chargers for both models.

On the 120 charger, the information plate states it has a 2.44 volt output with 14mA. I can only measure 1.2 to 1.25 volts output. I believe this means the charger is not working.

If I wanted to fix the charger, what would be the culprit inside? I opened the case, and there is little in there but the transformer, a diode and a capacitor. In regards to the charger for the 100 model, it is strange. It is actually a case that you put the radio into, close it and there are two prongs which rotate out, (to make the wall plug), and you plug the thing into the wall outlet. I had to be creative to check the voltage of this thing since you can’t access the contacts for the radio once the case is closed, and you have to close the case in order to plug it it. Anyway, when I measured the voltage on it, I got a 5.2 volt reading.

The info plate on the charger states: “Input: AC 105-125V” (next line down has): “50/60 c/s 1.2VA” Third line down has: “Output: DC 5mA MAX”. Is that output voltage of 5.2 volts correct for a NiCd battery of 2.4 volts? As I said, I’d really like to maintain as much of the sets as possible, at least on the outside, (I don’t think anyone would care that the batteries have been changed out for newer and better ones, and I am fine with replacing any internals, if possible, on the battery charger for either models). Thanks so much for nay help you can give me.

Talking about charging NiMh in room temperature, what about those solar garden light that have a single or more 1.2v NiMh in it that requires direct sunlight in order to charge the battery? Won’t the hot temperature under the sun kills the battery faster? What is your advice in this situation? On another matter, can I use a 5.5 V 100mA solar panel to charge a single 1.2v 2100mAh battery?

Assuming there will be only 6 hours of direct sunlight. Night time will be discharge thru some LEDs.

Thanks for your reply. I have the cells from a GEN II Prius and I wonder if I hook these up in series / paralled of 20 modules (14.2 volts series) with pairs paralled can these be floated on a 13.8 volt charger in an RV and then charges by the car’s alternator when being towed? Is there any advantage over a lead acid 12 volt battery for this application. I have the modules for sale on Ebay, but I could use them for my trailer. One day I hape to add solar panels to the trailer, but not currently. Thanks for any information.

To Steven who wrote on March 29th: You asked many questions and perhaps I can help you restore your Sony radios. Regarding the “120” charger: Many of the older, wall wart-type chargers seem to have a low output voltage until the battery is connected.

These chargers have deceivingly simple circuits, Some put out relatively pure DC; others output a somewhat half-wave, pulsed DC. So trying to measure the output voltage with a voltmeter can lead to erroneous readingsyou’d need an oscilloscope to view the waveform of the output. Here’s a simple test you can make: First measure the output on the voltmeter’s DCV range, the repeat on the ACV range. If the AC level is equal to or higher than the DC reading either the circuit is designed for pulsed charging or the capacitor is open.

So, you have two tests to make: the voltage with the battery connectedand the ACDC test. You may contact me directly at: shollis158@gmail.com. Dear battery Ir. Edward and others, I have a question regarding nimh type batteries. It is safe for me to tweak my nimh charger so that at the end of the charging process, the initial voltage of my nimh batteries would be at 1.6v instead of 1.2v.

Many of my colleagues do the same thing to their nimh batteries, but they aren’t sure about damages or dangers related to their act (tweaking their nimh chargers). For your information me and my colleagues are involved in certain indoor hobby that requires maximum amount of power to be drained out from our nimh batteries, and increasing the battery’s voltage to the highest possible value,while keeping the mAs constant seems to be a new trend among us. I’m still sticking to the traditional way of charging my own batteries, but recently i felt that i’ve been left behind by my colleagues.

Thank you for sharing your knowledge and experience with me and other readers. Hello, I am tasked to provide a battery operation feature for our alarm products. I was hoping I could get some questions answered. I plan on using a 7.2v @ 3000mAH NiMh battery pack for a battery-backed product that I am budgeting will use 100mA on average.

I plan to charge @ 0.2C and trickle charge at 0.03C. I will use a peak voltage to switch between charge and trickle charge. Keep in mind that the product is not a battery operated device, i.e. RC Car, but one that is battery backed for rare occurrences of loss of AC. My basic UL requirements are stated below. Voltage when charged: >=95%, 6.85V Voltage when discharged.

I would like to ask, how the charging current influence the battery life. If I will charge same batteries with 0.1C, 0.5C and 1C, how long they will last.

Also I read somewhere, that Nickle batteries act by the charging current. That means that with high current they are “harder” and charged with low current they will last longer in low current application. Is that true?

Or is better to charge sometimes the battery with higher current if I charge them for a long time with e.g. I supply certain electronic equipment that has standby battery operation for a few hours in the event of power failure. I used to use Ni Cads 4 AA 600mAh cells, now I am being forced to use Ni MH cells and I have been looking everywhere for as much information as possible since I do not want to risk my equipment catching fire or batteries exploding. My Ni cad batteries were on a trickle charge 24/7 365 days a year with about 25mA. I have not had any problems as the mains power rarely fails. I just use a simple 1watt resistor of 220 ohms to do this from a supply voltage of about 12 - 13v unregulated. Yes, most likely as.2c at that capacity probably won’t ignite the surrounding battery holder.

But it won’t bode well for battery life. Couple of things to consider: 1) NiCads are still available. You might want to take another look at what is forcing you to change. 2) There are very inexpensive smart charging ICs that will most likely prevent the overheating, memory, etc inherent in constant current, voltage limiting charge circuits. I’ve not kept up with them to be able to recommend a good choice. What will happen though, without some intelligent charge circuit is over time the usable capacity will decrease with the same measured voltage (at 5.6v) and it won’t be protecting anything (depending on current drain and length of time in protect mode).

I believe your next to last statement is on this point. Somehow you need to occasionally cycle the batteries with a discharge/charge cycle. You might want to switch to a LiPO battery depending on how much current you need while on battery power. They seem to be more suited to this type of protection scheme. I’m now using decent batteries (Eneloop AA and AAA) and a couple of decent intelligent chargers (both able to vary the input current) but I’m genuinely puzzled by all the information floating around the net about NiMH batteries. It all seemed very clear at first: Use as low a charging rate as possible to avoid the batteries getting hot - 200mA in my case. Then all sorts of advice started appearing about the ‘dangers’ of charging at too low a rate.

0.5C seemed to be the minimum acceptable charge rate. But having tried that (1000mA for a 2000 mAh battery) the battery’s still getting pretty warm, and that can’t be good. There seems to be little logic to all this - at least not logic I can follow. Batteries mustn’t get too warm, but they mustn’t be charged at less than 0.5C - these two statements appear to be inconsistent.

Can anyone provide a definitive answer on this, please? What’s the most appropriate charging rate for 1900 mAh AA and 750 mAh AAA Eneloops? With regard to temperature, charge rate and other variables related to charging batteries, it is generally accepted that one of the better ways to maximize the usable capacity of a charged battery is to detect the voltage drop that occurs at the peak charge capacity. In order to detect the peak, it is recommended that you charge at 0.5C. At less than.5C you can miss the drop (bad) or get a false drop (bad for capacity). Yes,.5C will increase the temperature of the battery during charge and I don’t know if temperature or charging at less than full capacity will damage the battery more quickly. Without rereading all the great doc assembled on this site (I haven’t worked on charges for a while), I would stick with.5C and monitor temperature which has the advantages of charging to the peak capacity while being one of the safest methods of detecting a runaway charger.

I did a lot of charts and statistics comparing charge rate with temperature and found that charging most (not all) batteries at.5C while monitoring the temperature for a hockey stick temperature increase offered the best overall method. So you need a deltaT algorithm in your charger.

As I teach above someplace, you really need to monitor temperature, time and voltage drop as well as over voltage, under voltage, low current and high current, basically all the factors, with temperature being the most important. You can burn your house down with a poorly monitored charger. Even a properly functioning charger could ignite certain materials or cause damage.

I use an aluminum heat sink under my batteries while charging. Edward has provided a lot of advice above on temperature over the years.

Hi Edward, I got a set of Motorola TLKR T80 EXTREME walkie-talkies which run on NiMH cells. According to the manual I am supposed to charge the charger pods (holding two of the walkie-talkies) with an AC-DC adapter which says “9V / 210mA” for 14 hours. A different radio model, the T81 HUNTER walkie-talkie, also ships with a 9V car charger which unfortunately is not available separately. Because of that I bought an alternative car charger which says “9V - 2.5 A” on the sticker. The retailer told me that charging my walkie-talkies with his car charger should not be a problem, even if the 250mA differs from the 2.5 A. Is that true?

I made a dual port cell phone charger each with its own battery bank of Ni-Mh (4) rechargable batteries, and toggle switch to keep them from discharging. Also, i connected both banks to its own usb with 1.2A output to charge phone faster. Im using one mini solar panel thats 6v 720 mA output to both banks. How long does it take to charge both sets of batteries. Im trying to charge a phone with a 3000 mAh battery. And how long will take to charge cell phone. With this in mind.

Do i need more solar panels or what to charge both banks. On February 13, 2016 at 7:54pm Mike.Hi MIke, there are NiMH cells classed for standby charging (such as in mobile handsets) Hi John! On March 28, 2016 at 6:57am John wrote.

Finally a man with a half of brain around here! (I mean, as, someone who has a clue what is he doing) The process of end charging (the remaining 30% of batt capacity) in NiMH and NiCd is about the same, hydrogen generation (protons, really) and recombination back into water is more pronounced, which leads to heating and pressure increase. The heating and pressure rise and all cause the battery voltage to rise, or even drop when the heat generation is too steep. This won’t happen on a too low charging current and the “INTELLIGENT” charger won’t correctly recognize when to stop.

That is why truly intelligent charging uses multiple termination methods (temperature rise, time-out timers, etc.) That is the reason why using too low current is not the best idea, dumb charger would be charging indefinitely. You know venting a battery is bad, because any leaked electrolyte can NOT be replenished, thus ending useful life prematurely. Hi Edward We are changing from LiFePO4 to NiMH due to shipping issues. I have some long experience with all battery technology However, on lifespan- we need 6+ years. Most of the battery manufacturers are hesitant to commit because they say corrosion of the caps is a problem.

I will need to investigate why. Do you have any comment on this? Also, your comments about battery charge detection are quite true. On our device with charge rate ~ 0.04C is is nearly impossible to figure out if it is charged complete or not. Especially with the load changing all the time. I’m curious if your high-end charger has temperature monitoring as this shouldn’t happen with one that does. Also, the higher-end charges sometimes have variable charge current and you shouldn’t exceed the charge specified.

Typically.5C is a good limit. Basically, if you have a charger that can deliver 5A into a battery with high internal resistance, it is possible to make the battery explode before the temperature sensor has time to react. If you read some of Edward’s (and my) earlier posts, your charger should include over-current protection, over and under voltage protection, temperature, etc and the all important failsafe, a timer. Putting even a short circuit across a charger with those protection schemes should result in a shutdown, not an explosion.

Couple of points: 1) Are you using default charge settings? 2) What are the charger settings and capacity of the batteries?

3) Are you sure they are NiMH and not NiCD? 4) Have you calculated the internal resistance of the batteries into a load? 5) Did you have the charger set for the right battery type? The questions are very basic since your problem shouldn’t happen.

I am curious about what charging settings I would use to charge 4 D cell Nimh 10,000mAh batteries wired in series? Can I even do this safely? I know they output 6V but do I go off of 10,000mAh or 40,000mAh capacity? I have a 680AC balance charger I use with my lipos which says it can change other battery types including nimh, nice, and pb. So, I’d like to leverage it if possible rather than buy another charger just for the d cells. How can I do this?

Btw, this is for my son’s robot which uses four D batteries and goes through them like nothing. Hi I’d like to build a slow charger (0.1C) for a NiMh battery pack made with 20 AA 1600mAh cells in series (24volts).

Someone told me that it’s dangerous to have so many cells in series because it’s more likely that one of the cells fails and compromise the entire pack. I’d like to control the charging circuit with an arduino. Can you point me to a well designed charging circuit schematic?

Should I monitor the voltage of the entire pack only or it’s better to monitor also the voltage at half pack? Hello I know nothing about charge rates etc. However, I will state all of my details and hope someone can help me out. I have an old Bearcat scanner (200xlt) that used a battery pack BP200 which contains 6 Ni-Cad batteries, 600mAh and 7.2 Volts.

Most people rebuild them with NiMH batteries however, my battery pack is a slight bit corroded inside and there is a red wire that has come off from somewhere. The replacement is a battery pack with NiMH batteries, 7.2 Vorlts and 1800 mAh. I guess my question is: will the original charger (Uniden model number AD-140U) which supplies input of 120V at 60Hz and 14W and a DC output of 12V and500mA work for the new battery pack?

If I have missed any information to formulate the proper answer please let me know and thank you for your help. Jim, Without knowing more about your application, it would be difficult for me to make specific AND safe recommendations. Instead, I’ll share some of my experience with charging NiMH cells.

First, the terms “trickle” and “float” when applied to charging cells of other than lead-acid chemistry can be very problematic. Yes, we use these terms in a general way with cells of other chemistries, but we should realize we’re on shaky ground! Second, the Ace R/C Company manufactured a charger that automatically followed a normal charge with a continuous “trickle” charge. I have been using one of these chargers for over twenty years with no ill effects to both NiCd and NiMH cells. The NiMH battery packs in my R/C airplanes charge continuously all winter with only good results! The charging protocol used by Ace R/C is called “pulse” charging. Quoting from the charger’s manual: “Battery manufacturers (such as Sanyo) recognize the pulsed charging concept as a preferred and safe technique for charging both ni-cd and NiMH batteries.” If this interests you and you need more info, please reply.

Hi, I need some advice about before buying a new battery charge for my Ebike. It is 24 volt with 10 separate batteries wired together. The original charger got wet and failed. I bought a cheap 24 volt charger off ebay which worked for a while but the batteries would not hold much charge so I had them all replaced. After that it took ages to charge ( 10- 20 hours instead of 5) and the battery got really hot. The charger failed and the plastic case melted.I now know this is bad and will shorten their life.

It is very hard to find a replacement charger. There are some made for Razor scooters but I having researched that line find they are designed for lead acid batteries. I think that is the one I bought which melted.

If I buy another one of these and only charge for 5-6 hrs would this be OK. I’m really missing my ebike and have forked out for new batteries am keen to get back on the road. Is my base-station for my wireless headphone damaging my batteries by overcharging if I place them on it every night to charge the batteries? I only use the headphones a few hours a day, at most, and they seem to work at least a week before the batteries are too weak(the only indication of this is distorted sound and the headphone has a green ON LED that gets dimmer and dimmer as the battery charge depletes. This is the case, of course, if I don’t place the headphones on the charger for charging, but I do remember to turn off the headphones with a press upon the on/off toggle switch on the headphones after use. I do not like the inconvenience of waiting for the headphones to charge the two internal Accu 800 mAH NiMH AAA cells if I let the batteries go dry, but I also don’t want to overcharge these two cells and shorten their usable life by always placing the headphones back on the base station each day after use.

The open circuit voltage measured at the base station charging terminals is 7.5V, but when loaded with a 100-ohm resistor, it drops to 3.0V. When loaded with a 1K resistor, the voltage drops to 6V. Also, when the batteries have reached 1.33V each during charging, the charging current measured is 50mA. There is a only a single red LED on the base station that shows the batteries are being charged and no other indication that the batteries are fully charged or not. Since I am a electronics guy, I know how to build into the base station a voltage clamp circuit to limit the battery charging voltage to somewhere between 3.0 V to 3.2V to prevent overcharging. My circuit would function as a precision shunt regulator and would limit the max.

Charging float voltage to 1.5V or 1.6V per cell. Current limiting is already part of the original charging circuit.

Would this simple voltage-clamp fix idea work best to get the best battery life charging life? If this method is a good solution, then would 1.5V/cell max. Work better than 1.6V? Final question, is it better to each day recharge NiMH batteries after each use or wait for the battery to be closer to complete discharge before recharging for best battery service life?

The science of “charging” is simply the transfer of electrical charge (electrons) from source (charger) to destination (battery). The details depend on cell chemistry. NiMH cells are said to prefer “slow” charge rates (as compared to NiCd cells), especially for the initial charge. Slow charge rate is generally rated as one-tenth C or less.

Your battery is C-rated at 3000mAh (3Ah) so slow is 300mA. So 100mA would be a nice, really slow initial charge rate. How much time is needed for a full charge? 3000 divided by 100 equals 30 hours, but since your battery is hopefully not dead, that is: zero charge (not good for the battery), 24 hours should be long enough.

If the battery gets warm to the touch, it’s probably in over-charge. Hi There, I am building some battery powered Remote Ultrasonic senors which use LORA radios to send data. The basic design uses 3 D cells. We have 10 prototypes running and reporting data. I got to thinking it would be cool to put some little solar panels on the box and see if I could extend the run time with a little help from the sun. I modified one of my units to accept a solar input via a diode to the battery pack.

This is a series string so the battery voltage is about 3.6 for NiMH. The solar panes are small and only put out about 5V open circuit. I am loosing about.3v across the diode. I just set it up it seems to run, just not sure about charging a 3 cell stack. I am always going to be less then.1C.

Our circuit is on for 1.2 seconds and off for 20 seconds (or 24 hours) for this test so the idea was in the off state the panels would trickle charge the batteries allowing them to perhaps not discharge ever in situations where we were only reading a few times a day. This is my first attempt at charging a NiMH battery. IT looks like they can be quite complicated if you are in a hurry or very concerned about 100% charge. My circuit will work with input voltages from 2.9 to 5v. We got 120K reads out of 3 Dcell Alkiline batteries. This solar charge idea is only for NiMH batteries. Can I kill MiNH batteries by over trickle charging them?

Adding an active charge termination circuit would probably not be to hard. Majda Volk and Marty Simmons – Sorry for my delay in posting this reply Majda: I answered your question (I hope) above on 9-15-17 at 9:14am, but neglected to add you name to the post. Now to Marty: Over the years, I’ve owned several consumer appliances with rechargeable batteries. Some were designed to be charged for a specified number of hours; leaving the battery on charge beyond that time limit “may shorten battery life,” or so the instructions said. However, other appliances I have: a camera, toothbrush and shaver can be left on their charging docks 24/7, month after monthno problem!

Obviously the charging circuitry maintains the charge at a safe level and/or shuts off the charge completely when charging is completed. Bottom line: The instructions for the appliance should say if it can or cannot be left on charge continuously. I leave my Sennheiser RS160 wireless headphones connected to the charger after each use. The LED on the right headphone turns off when the charge is completed, but I leave the charge cord connected until the next use. I’ve been doing this for about 3 years with no problem. So the instructions rule. No instructions?

Please read the introductory information at the beginning of this thread: “BU-408: Charging Nickel-metal-hydride Know how to apply the correct charge to moderate heat and prevent overcharge.” This explains why moderating (controlling) cell temperature is critical to getting a complete charge and prolonging cell life. BTW: I purchased a case of “surplus,” Panasonic 1100mAh, NiMH cells at least 15 years ago. With careful charging, most still work to spec!!!

You mentioned the open-circuit voltage, etc. But the key parameter here is current, that is: charge flow. In order to cause a charge flow, the voltage of the charge source (the charger) must be greater than the voltage of the battery. In order to completely charge a battery, the charger voltage must be greater than the fully-charged voltage of the battery.

That’s why the charger’s voltage is higher than the battery voltage. Steve Hollis. I want to thank Jerry for his reply of 17th February 2016, I didn’t see reply earlier and only saw it now, since for some reason I did not receive any email notification. But many thanks Jerry for your reply.

I’m ‘old school’ where NiCd cell &/or battery capacities were determined by the energy one could extract from a factory-new item during a carefully chosen ten hour discharge that took the cell(s) at a constant rate to the practical exhaustion point. If the manufacturer claimed 5000 mAh capacity I should be able to take a new recently exercised cell, apply a constant C÷10 load and expect the cell to deliver that current for ten hours before the voltage plummeted. Question 1: is a discharge rate of “C over ten” still the standard for nickle metal hydride cells? Question 2: Ditto for Lithium Ion and cells with increasing power density? I have a Colman lantern, it has 4 removable led panels each using 3 AAA Ni-MH rechargable batteries. The base has 8 D size Duracell which I assume recharges these panels as needed, and did so for several years.

Now two of these panels don’t hold a charge, they don’t light when seperated from the base like the others do, but do light when attached to the base. I am not an engineer and new to this type of battery, can I assume that these size D’s is the best way to recharge these panels, and replaceing these AAA Ni-MHs should fix this problem? This lantern is important to my emergency kit and has been used twice just this season when we had no power for an extended time.

I hate to replace it, when a little knowledge and new batteries would fix it. Thanks for your help and expertise.

Marcia, whether to repair or replace your lantern is problematic. This product has a history of defects that may be repairable, but not at less than the cost of replacement - unless you can do the repairs yourself or have a friend who can do it for you. One of the reported issues with this lantern is internal corrosion. (Whenever I purchase a product like this, I spray the battery areas with CRC 2-26, a product sold at Home Depot, in the electrical dept, in a 5oz.

This has saved many a battery-powered device.) Corrosion may be the problem with your lantern. Or, it could be some defective AAA cells - easily checked with a voltmeter, if there is easy access.

I have a custom made battery pack made out of 324 Panasonic AA Eneloop batteries (Eneloop AA factory spec = 1.2 V/1900 mAh/1.9Ah; actual tested fully charged spec = 1.43V/1,850 mAh/1.85 Ah which I will use for this purpose). Said battery pack has 9 AA batteries wired in parallel per column (9 x 1.43V = 12.87V/1.85 Ah per column) x 36 columns wired in series (36 x 1.85 Ah = 66.6Ah/12.87V battery pack). When the battery pack is fully charged it reads 12.8VA freaking awesome 12.8 V/66.6 Ah battery pack that just keeps on going and going and going. However, when it comes time to charge the batteries, I spend about 45 min taking the batteries out and putting them into the 4 bank charges that came with the batteries, then another 45 min taking them out of the chargers to put them back into the battery pack which is a royal pain in the butt. I was told it would take a 10 amp battery charger to charge the battery pack as a whole. However, I want to charge exactly to 12,8V of which there are no chargers with sufficient amperage I can find to accomplish this.

I was told that I would be better off using a 12 VDC 10 amp variable power supply, in lieu of a battery charger, so that I can fine-tune the charge to 12.8 V exactly. Questions: 1. Is it true that I can use a variable power supply to charge the batter pack in lieu of a battery charger?

As long as I set the constant voltage of the variable power supply to 12.8V, is it true that there is no danger of overcharging because the 12.8V output of the power supply will not exceed the 12.8V of the battery pack when fully charged? As the 324 AA Eneloop batteries in the battery pack get older will the 12.8V battery pack output drop to less voltage over time thereby making it possible I could overcharge the battery pack by charging at 12.8V over time?

Was I told correctly that 10 amps would be sufficient to charge the 66.6 Ah battery pack, again, said battery pack is made from 324 AA Panasonic Eneloop batteries? Thanks for any help you can provide in this regard. John. I am using Panasonic AA Eneloop batteries: As you can see (charging current x time) is: 1. 2000mA x 1.1h for fast charge rate 2. 200mA x 16h for normal charge rate 1. Does this mean for a fast charge that for one AA 2000/1900 mAh battery that I should charge it for 1.1 hours @ 2000mA for a full charge? Does that mean for a normal charge that I should charge one battery for 16 hours @ 200mA for a full charge?

Just a novice, trying to figure the preferred fast charge and normal charge rates according the exact specs of the battery in the link above. Thanks, John. Do you have a way to plot the output voltage of your charger? The chargers I’ve built have always had USB/serial interfaces for that reason.

The typical NiMH batter delta V is only like 20mv per cell and you have to be using a substantial charge rate to even generate the delta. I believe you need more charge time at.4C, maybe as much as 3.75hrs as you are only charging to capacity at 2.5hrs. If you had a perfect charger that would be fine but you don’t and there is no such thing. You need to be checking the temperature at all times with cells of that capacity as the risk of fire is great, especially when you have so many cells and you don’t know the status of each cell. The best thing to do is monitor your charge voltage and current (constant), plot it out and see if there is a peak and delta V you can detect. As previously stated, if you are building your own charger, you need to check for initial short circuits or opens, high or low initial voltage, peak voltage, charge time and temperature as well as delta V with cutoffs or initial rejection of the battery if it fails any of the tests. By the way, depending on the micro controller ADC, make sure it has the resolution to detect the delta V.

If not, you can use a peak charging capacitor with a comparator but you have to play with the comparator sensitivity so it doesn’t kick out with the slightest noise.