Charging batteries in series

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joey_picus
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Re: Charging batteries in series

Post by joey_picus »

For the one JST-pH pack I have I made up an adaptor lead which works fairly well - I would avoid using crocodile clips because the dangers of short-circuiting LiPos in particular are great enough that you really don't want any risk of that happening (although then I'm not reknowned for steady hands at the best of times...)

Most of my batteries are plain 2 cell packs with no balance leads, and I've never had any issue charging those using a simple auto-detecting charger - if you're concerned about charging times, the best solution would be to mount the battery pack/cells so they can be switched out easily and have more than one set, so you can be charging one while fighting with another.
Joey McConnell-Farber - Team Picus Telerobotics - http://picus.org.uk/ - @joey_picus
"These dreams go on when I close my eyes...every second of the night, I live another life"
Sportball
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Joined: Mon Sep 23, 2013 7:29 pm

Re: Charging batteries in series

Post by Sportball »

Thanks for the advice. I have successfully soldered up some tiny JST pH sockets that allow me to plug in each 1c battery indepentally although they are in series on the robot. Both charged within 1hr so no problem there.
Sportball
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Re: Charging batteries in series

Post by Sportball »

I have left my robot on and drained the batteries after only 3 charges. From what I understand the charger looks for a voltage range before it will work. Can they be revived?

My idea is to order 2 more and charge 1 dead with 1 good one to get the voltage up enough so they can then be charged indepentantly, will this work?
razerdave
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Re: Charging batteries in series

Post by razerdave »

If its a lipo, then no. Don't try and revive them. Learn your lesson and get some new ones.
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BeligerAnt
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Re: Charging batteries in series

Post by BeligerAnt »

Depending on the charger, it may be able to charge them. And if they have over-discharged due to being left "on" but not running the cells should be recoverable. Charging a "good" cell in series with a "bad" one will kill the already wounded cell!

There is a minimum voltage of around 2.5V per cell. Below this voltage they don't take kindly to being charged at a (relatively) high current. Normal charging current is around 1C where C is the capacity, so 100mA for a 100mAh cell, 200mA for a 200mAh cell and so on.

If you're lucky, your charger will detect the voltage as being too low and will apply a very small current to the cell to slowly charge it, then when the voltage reaches 2.5V automatically start charging at the proper rate.
If you're not so lucky, the charger will detect the voltage and just sulk and refuse to charge the battery at all.
If you're really unlucky, the charger will not detect the voltage and will try to charge the battery and kill it - if this happens, get a different charger!

Since it sounds like your charger is in the "just sulks" category, you could try applying a very small current ( less than 0.1C) to the cell and monitor the voltage, stopping when the voltage reaches 2.75V or so. Then you should be able to charge the cell fully using your charger.
Gary, Team BeligerAnt
Sportball
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Re: Charging batteries in series

Post by Sportball »

Thanks for the advice, I have ordered 2 replacements and will keep these separated. My friend has a NiMH charger that may allow me to charge them slowly.

I believe my charger is indeed "sulking" it is a Sky RC E4 and is showing warning light and refusing to even attempt to charge them.

Kill or Cure I say!
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