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Old 28th November 2006, 02:09 PM   #1
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Default What voltage must supply to charge a 1.2 battery?

I want to make a 12V battery pack with 10 1.2 volt batteries. I tried to charge it with a 12V power supply but seems is not enough, so I would need a superior voltage, but what one?
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Old 28th November 2006, 02:31 PM   #2
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The charge supply voltage must be higher than the battery terminal voltage. Then you put a current limit resistor inline with the supply to achieve what charge current you need. You thenmonitor the battery voltage to either cut it off at a predetermined voltage, or look for the 'peak'.

If you just put a 12v DC supply onto a flat battery pack you might have damaged the battery pack.
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Old 28th November 2006, 02:39 PM   #3
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by richie00boy
The charge supply voltage must be higher than the battery terminal voltage. Then you put a current limit resistor inline with the supply to achieve what charge current you need. You thenmonitor the battery voltage to either cut it off at a predetermined voltage, or look for the 'peak'.

If you just put a 12v DC supply onto a flat battery pack you might have damaged the battery pack.

Hi, i presume they are not lead acid batteries, /sreten.
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Old 28th November 2006, 02:43 PM   #4
Ghianni is offline Ghianni  Greece
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If the batteries are NiCd type then they must be charged by a current source at 1/10 of mAH of cell capacity, ie 1200 mAH cell at 120 mA for about 16 hours.
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Old 28th November 2006, 02:45 PM   #5
djQUAN is offline djQUAN  Philippines
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Quote:
Originally posted by sreten



Hi, i presume they are not lead acid batteries, /sreten.


he said 10 1.2V cells so they are either Ni-Cd or Ni-MH cells.

either way, they need to be charged constant current and the current depending on the cell Ah rating.

detecting full charge is different on both cells but the Ni-MH is a little easier to detect. the cells heat up when they are fully charged. leaving them to overcharge will lead to cell damage or explosion though so you should be careful.
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Old 28th November 2006, 04:20 PM   #6
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I was refering to Ni-MH 1.2 batteries at 2600mah, but have also lead acid batteries.
It seems that I have damaged the lead ones, because just have conected 12V power supply to them, and now they have very low capacity

Well, I understood the current setting, if I would need 260 ma, isnīt?
So, I= V/R where V=12V and I 0,26A, so the R I need is 46 ohm?

Are not avaible chargers for 12V operation? I have one for charging the indidual batteries, but have not found on electronic stores one to can charge a 12V pack..
And what voltage should I use? 13V? 14V?
And what about the led to know when is charged?
If there is avaible a 12V charger for sale would be really nice, and better if is voltage variable. 10.8 V etc..
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Old 28th November 2006, 04:40 PM   #7
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Good that you saw you need to use ohms law, but you got the voltage bit wrong. The voltage you use is the drive voltage - full battery voltage, e.g. with 15V supply and 12V battery, it's 3V.
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Old 29th November 2006, 01:19 PM   #8
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ah, ok, but still there is the issue of the when to stop, I think would be better buying a smart charger. I have found afordable at 20$ + shiping on ebay for any voltage from 9.6 to 18v. It detects automatically the voltage. Current draw selectable.
But there are two types for NIMH/ NICD and for Li-ON.
The thing is that I have some cells of a laptop broken battery at 10.8 V, and also have bought 12 battery AA size batteries for 10 euro. They are 2600 mah. So each 12V pack for 2600 mah would be only 10 euro.
But I would need more mah, and need to buy more batteries. But what do you think is the best capacity/price ratio, Li-ion batteries, or NI-MH ones? I should better buy all the same to can use just one charger.
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Old 29th November 2006, 01:45 PM   #9
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The type you need will depend on the application - length of 'ready for action' time needed, current draw, recharge rate etc.
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Old 29th November 2006, 01:57 PM   #10
djQUAN is offline djQUAN  Philippines
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it must be noted that Li-ION cells are the least forgiving in charge method.

if you don't follow the charging scheme for a Li-ION cell, the least that would happen is instant damage to the cell. and the worst, well, explosion is one.

I would suggest to stick to Ni-MH since they are a bit more forgiving and simply require a constant current charging method.


I would like to vote for a thread discussing battery types, charging methods, and possible risks in different types..........what do you guys think?
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