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# can i charge 10X1.2v 3000ma rechargeable batteries in series using a 12 volt 400ma current ? Answered

i am building a r/c tank and i am using 30 1.2v 3A rechargeable nimh batteries. now i have tried charging them individually in my energizer battery charger, but they seem to get extremely hot (75 celcius) when i charge them for 2 hours. now in the tank i have these batteries in 3 battery packs that hold 10 batteries each and i want to know, if i put a 12 volt 400-500ma current through the battery pack, will that safely charge them without damaging them? recently i tested one of the hot nimh batteries out of the charger with my multimeter, and it read that the battery had 10.28 amps in it and had1.2 volts which is anbormal (exept for the voltage).also i was wondering, is it posible tocharge these packs which once run in parrell give a voltage and current of this
(10X 1.2 =12 volt 3A) X 3 packs in parrell =12v 9A

can i chareg all of those at the same time, or must i charge one pack at the same time

now before you say anything ill just add that these are individual batteries that i have placed inside a battery holder pack, also ill add that i wont buy a sla battery as ive used quite alot of money on these batteries already and lastly, i am not going to go buy a 10 battery charger as they cost way too much, unless sopmeone can find one online that costs under \$25

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## Discussions

Yes and no.

Yes, it will charge them, but if there are any inconsistencies in the voltage between indiviual cells, they will be out of BALANCE.

Also keep in mind, they are 3000 mAH (hours) not miliamp. miliamp is a flowrate, miliamp hours (rate times time) is a total volume.

Batteries will take any charge you give them (within reason) -- so long as they can absorb it, its simply like filling a bathtub.
Based on that, 3000maH charging at 400mA would take 3000maH/400ma = 7.5 h.

Back to that balance problem -- if one cell is 1.0 volts and the rest are .9 volts, when it charges, they will all go up at the same rate, but the one will get to 1.2v and be charged while the others will be at 1.1, still charging. What happens next? You get a splodey sad situation. There are 'balancing chargers' that use various methods to ensure all the batteries are the same.

oh, well thats not realy a problem as i can discharge them in my camera, so if they are all discharged with no electricity in them, then will they be able to be safely charged?

although with something like that i dont want to risk explosion, could you possibly give me a link to a charger for sale that can charge 10 nimh batteries such as mine safely without the splody sad situation, with what you said was a balancing charger, i just had a lok on ebay and there are only ones for \$56 and theyre for li-po batteries as well and dont seem to be for aa batteries

lipo is the most common culprit because of a few problems: they must not be over or UNDER charged, or they a) become useless, b) start on fire. Balancing is a MUST for LIPO.

What you are suggesting as 'charge them all in series' causes the same problem -- but as the cells are more tolerant to voltage differences you may encounter. Balancing chargers are expensive and complicated. -- such is life.

As for charging each cell individually, the 10 cells again poses a challenge because of the annoyance of actually taking them out and charging them one at a time. Individual tiny chargers can be built (look for nimh charger circuit) and build 10 of those to run in parallel.

the main hassle is that they are all looking the same and i cant really tell if they are fully charged or not if they get mixed up if i charge them in sets if 4, plus im worryd theyll blow up in my energizer charger

as for mini charegrs for each battery, that cannot be done either simmply becasue the battery holder has no rrom for it, although it is a good idea, i just cant.