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How to charge 4AA NiMH 1,2V 1100mAh in series? Answered

My project is a simple portable stereo box - using old USB powered speakers.I put the speakers with their little amp board in a box where I can put a 3-4NiMH rechargeble batteries 1,2V 1100mAh(in series for ~4-5V) to charge the amp board. I really want to make it so I can just plug an USB (5V) to the box to recharge the batteries when its not used so i dont have to take them out to recharge them with a wall charger everytime.I would like it to have LEDs to tell me when its charging and when its done , or even that it stops charging automatically when the batteries are charged. Im fairly new to electronics so I need the easiest way to do this if possible 

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steveastrouk

Best Answer 2 years ago

NiMh are pretty tolerant battery chemistries.

Series charging is perfectly normal - that's how battery powered tools using NiMh do it. 150mA is a little more than I'd like to charge them at, 110mA would be a 10hour rate, and they'll take that for quite some time, with no active control, other than current. Of course its better to have something monitoring the voltage and terminating the charge properly, but a C/10 rate works - if you can afford to go slower with a dumb charger, its probably better,.

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AndrianSsteveastrouk

Answer 2 years ago

actually just checked again my mistake my charger charges at 1,2V 120mA not 150mA, so basically - 4 batteries in series would take 4,8V-5V and about 400-450mA to charge safely with a 10h charge time ? And maybe add something to stop the charging when the batteries reach a set total voltage. Main problem is space is very limited

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steveastroukAndrianS

Answer 2 years ago

The batteries need constant CURRENT charging. If the capacity of the stack is 1100mA, say, all in series need charging at 110mA.

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AndrianSsteveastrouk

Answer 2 years ago

4 x batteries - each as it says on the battery is 1100mAh 1,2V , i will be connecting them in series so the output is around 5-6V because the USB speakers work at 5V but i have tried and they work with 3x batteries too so im guessing 4x batteries wont be a problem. I dont want a fast charger , charge time isnt an issue so i prefer something slow but safe if its left to charge over the recomended time - lest say you should charge them for abut 10h , and it wouldnt be a problem to leave them for 12-13 hours or so.So I need to know what V and mA supply do I need to charge 3x and 4x batteries (1100mAh 1,2V each) at - if 1 battery charges at 1,2V 120mA do i just multiply x3 and x4 to get what i need or some other way to determine what I need to supply them with.

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AndrianSAndrianS

Answer 2 years ago

Lets say I get a USB supply that is rated to give out 5v 450mA - would that be safe and correct way to charge a 4xbattery pack with batteries connected in series and each battery rated at 1,2V 1100mAh

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steveastroukAndrianS

Answer 2 years ago

You have very little range to work with to charge them from a supply that low, since 4 x 1.2 = 4.8V. Try it, with a 12Ohm resistor to limit the current. Measure the current. A 1/4W resistor should work fine.

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AndrianSsteveastrouk

Answer 2 years ago

ok so what would be the best safest option to charge the mentioned batteries in series .and maybe (just maybe) 2 packs of 4batteries connected in parallel to prolong the life of the audio system.

So 4xbatteries 1,2V NiMH in series - how to calculate what V and mA I need to slow safe charge them

and (4xbatteries 1,2 NiMH in series) x2 connected in parallel -how to calculate what V and mA I need to slow safe charge them

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steveastroukAndrianS

Answer 2 years ago

I did it for you, based on a nominal battery voltage of around 1.15, fully discharged.

Two in parallel, you can just do with a 12 Ohm resistor in series with each bank. I really don't guarantee it will charge on 5V though. Like I SAID measure it.

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iceng

2 years ago

NiMH batteries have a memory of last recharge and deliver only the fractional charge used... To restore a NiMH battery to full capacity it is necessary to fully discharge and recharge it several times... There is no easiest way to do this that I know of short of buy a charger.

You could try this. https://www.instructables.com/id/How-to-Make-a-NiMH...

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AndrianSiceng

Answer 2 years ago

buying a charger isnt a problem , the problem is they will be connected in series for ~5V and the wall chargers are usually made to charge every battery separately not in series , my old charger that ive been using for years puts out 1,2V 150mA per battery slot with 2 slots .Taking that as an example I was thinking of 1,2v 150mA x 4 = ~4,8-5V 600mA current maybe will charge the 4 batteries in series but I want to be sure before I try is. I have like 10 or more of those batteries