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Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
I've got a homemade pack of lithium ion batteries (18650's), and a pack of NiCd batteries (from a drill pack), but neither have a designated charger for them anymore.
I know that using a camera charger or something along those lines is doable, but these are pretty large packs, both are rated at around 14 volts.
From what I understand, NiCd batteries are the easiest type of battery maintenance wise, and charging wise in most cases.
Lithiums, are finicky, and are somewhat dangerous when charged without a "specially made" charger, designed for lithiums
Feel free to correct me on any of my statements.
So, I was wondering, is it possible to make a "dumb" charger to charge the packs? (I'll probably end up dismantling the li-ion one, so I can balance the cells...) Something like a buck regulator, or a linear reg with a turn off sensor once a specified voltage is reached, to prevent overcharging?
Or, should I just go with a "safer" route and use an IC designed to charge Lithium ion batteries, and then what about the NiCd ones?
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
I have seen inside some lithium chargers for power tools and they were very simple. It looked like they assumed that the cells were perfectly matched and used a temperature sensor as a failsafe in case anything went horribly wrong.
Since you are asking these questions I don't think you should make your own lithium charger because if you do it really wrong they can burst into flames.
NiCd batteries will just get very hot and in a really bad case spew some poison at you. But they are more complicated to charge than lithium batteries since it is harder to detect a full charge. What will always work is to charge them until they start to heat up, then you know they are full. Alternatively charge them at a low enough current that they take no damage even if you forget to disconnect the charger.
In both cases the useful lifetime depends strongly on the quality of your charging.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
The only dumb charger you can make for either of those chemistries is a low current trickle charger < C/14 for NiCds.
If you trickle charge lithiums, you'll kill them real fast.
A fast charger for either chemistry needs a good end-point.
The classic end point for NiCds is to notice when the terminal voltage drops while constant current charging - this is an indirect indication of the sudden rise in temperature causing the internal resistance to drop. But it needs a good constant charge current, variations in that will obscure the variation you're looking for. As Bjorn says, it's more reliable to sense the temperature directly.
There is an easy way to fast charge lithiums to 70/80% of full charge, and that's to use constant current and to stop at 4.2v. Some naughty commercial fast chargers do this, without mentioning that they don't acheive 100% capacity. To get to 100%, you then need to switch to constant 4.2v and stop when the charge current has dropped to <C/10. And both of those stops mean stop, don't continue to trickle.
Registered Member #2063
Joined: Sat Apr 04 2009, 03:16PM
Location: Toronto
Posts: 352
quick question about lithium ion batteries. do they do bad if its left discharged for a long period of time (30+ days). my old phone's Li-on battery is pretty much dead, can't even last 2 days on standby. prabably because I left it uncharged for a month
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Is it possible to charge rechargeable batteries without a "smart" charger?
