Charger

[kimbear]

I have a battery pack that will be inside a sealed waterproof case that consists of 6-NIMH AA batteries.
What charger should I use for this, and how should the batteries be charged...individually, or as a group?
What charger should I use??
I would use a standard Lipo, and charge it via the charge connector, but there is no way to waterproof the multi-pin LIpo charge connector...or is there???
Whatcha think???
Thanks in advance

 

[AnalogKid]

For best performance, longest life, and safety, rechargeable batteries always should be recharged individually. When charged in series there is no way to guarantee they all will be completely recharged. Also, it is much more difficult to isolate a failed cell.

Separate from that, a LIPO battery requires a very different charging profile than a NiMH. Better to use a charger optimized for the chemistry you are using.

ak

 

[kimbear]

Ok, so what about NiCads??

 

[Nigel Goodwin]

All three require different chargers - Li-Ion are the most popular type these days, and there are plenty of very cheap charger boards available for them.

 

[rjenkinsgb]

You could use NiMH with a combination charge system; current limited constant voltage to possibly 1.45V per cell plus a trickle charge of 0.05C for a few hours to top them off.

That can be as simple as a voltage regulator plus a resistor, calculated so the current drops to 0.05C (= C / 20, the max current for continuous trickle) before the cells reach maximum voltage.

For a lithium pack, you need a an appropriate charge controller plus an "protection" board to prevent overall over- or under-voltage.
And, for anything with two or more cells in series, a "balance controller".
It's the balance part that needs the multi-pin connection, but you can easily get balance controller boards to build in to battery packs.

Lack of a balance controller somewhere is one of the common causes of cells bursting or catching fire, as a slight capacity difference can mean one cell overcharges before the overall pack voltage reaches full charge level...

Examples
Protection board: **broken link removed**

Balancing board: **broken link removed**

The protection boards sometimes have balance circuitry as well, but that may be rated at far too low current to be useful.
My rule-of-thumb is the balance circuit should be rated at least 10% of the max charge current and preferably higher.
That may be excess, but for a trivial price I'd rather avoid burst cells...

With those in the battery casing, you can then treat it as a two-terminal pack and use a separate two cell charger without extra balance connections.