Unconventional NiMH charging question...

[shankus]

I'm wondering if two NiMH AAAs can be charged in a single slot in parallel.

I have a rechargeable reading light in mind, and the idea calls for two AAA NiMH in a project case that screws shut. In a perfect world, I'd like to put a mini headphone jack into it for charging, with a two conductor running to a dummy cell that would plug into a standard cell charger.

Is that feasible? Perhaps it would depend on the charger. I plan on using the Maha 401 mostly, but not exclusively. I'd like it to be universal, though.

I don't think the charger would know the difference between two AAA 700-800 mAh, and a single AA of a higher capacity, right?
When the cells are charged, the charger should terminate the cycle correctly, as long as it doesn't use delta/temp for charge termination.
Am I missing something?

 

[eluminator]

I think it would work. Several commercial chargers do this including my favorite, the C Crane.

After all, couldn't you consider an AA cell to be just 2 or 3 AAA cells in parallel?

 

[Christoph]

If one of the cells would be come fully charged befor the other it would get over charged(HOT) and possibly damaged.IMHO
others here know more
Chris

 

[shankus]

It would do that in a normal parallel charger, though, wouldn't it?

 

[Christoph]

Maybe thats why I have no chargers that charge in that manner.I have started using R/C chargers and like the versatility with charge rates and times and even delta/temp changes.
Chris /ubbthreads/images/graemlins/grin.gif

 

[shankus]

That's exactly why I have no parallel chargers. I was just wondering how well it would work. The cells installed in the light would be dedicated to that light only.

If I got a few hundred charges out of the cells, I'd be satisfied.

 

[Christoph]

It might be fine that way with the occasional slow charge to equalize the cells. I'm working on something using parallel LI-ION cells semi-perm construction. with either external jack or inductive charging.
Chris

 

[Unicorn]

Wouldn't that be the same as charging a light with a shrinkwrapped battery pack? Stinger, Ultra/Superstinger, MagCharger, SureFire 8AX and 9AN for Ni-cad, and the Tigerlight for NiMH. What keeps those from having one cell overcharged? Are the battery packs in general just nearly perfectly matched so that it's unlikely that one will become overcharged when charging? Or even a single cell becoming overdischarged? Assuming that you don't run the light until the bulb no longer lights up.

 

[Doug Owen]

First off, I assume the two cells are already in parallel, that is you're not reconfiguring it just to make charging more fun?

I too see no real problem. Reliability is of course an issue, if either cell dies, nothing (unless it fails to open). Series parallel is common scheme for a number of reasons. I say 'go for it'.

Doug Owen

 

[Ray_of_Light]

I second what Doug said. Technically, I may want to suggest you a current limited charger.

I charge my PT Surge (4 x 1850 mA + 4 x 1850 mA in parallel) by using the light bulb as charge limiter. (Surge open!)

Consider that, for various reasons, it is not possible to trickle charge Ni-MH in parallel.

Regards

Anthony

 

[shankus]

The piture I have in my mind, is two AAA NiMH, in parallel inside the light, feeding it's circuitry in parallel.
Then, a pair of wires would be plugged into a mini-headphone jack on the light, and be connected at the other end, to a dummy cell, that will plug into a charger. The cells would be charged & discharged in parallel.

 

[kitelights]

The AA and AAA charging rates are different on the 401. I don't know what the specs are, but they are different. I doubt you'd get both cells charged in a single AAA slot. I guess you could use an AA slot and dummy instead.

 

[Brock]

I would think it would be fine. I would occasionally take them out and charge them separately.

I would also use the slow charge on the 401 since they are sealed in a case, they might get pretty warm. Better safe then sorry.