[Coco] OT: Battery chargers

[gene heskett]

On Saturday, October 15, 2011 02:27:07 PM Tony Schountz did opine:

> Sorry for the OT post, but you guys are about the source of information
> on electronics.
> 
> I have a Rolleiflex SLX camera that has a 10V battery pack (actually,
> 1.2v x 8 cells = 9.6v). The original had NiCd cells and a dedicated
> charger, but the charger doesn't work and the cells were dead. So I
> thought I could put 1400 mAh NiMH cells in it and use my PowerEX 9V
> "smart" charger (which puts out 11V at 200 mAh). When I connect the
> battery to the charger it takes about 7 hours to fully charge (charger
> light turns green), which is about what it should be based upon its mAh
> output and the mAh of the batteries. However, if I don't even use the
> camera, the cells deplete in about 2 weeks, such that I need to
> recharge the pack. I've put in two sets of batteries and the problem
> persists, so I don't think it's the batteries themselves.

More than likely is is Tony, NiMH batteries have a higher self discharge 
rate than NiCads.  Couple that with the miss-match between the charger and 
the cells, it could be that they are not being fully charged.  Most Nicad 
chargers use a temp switch in the batteries (the third connection to the 
charger) which turns the charger off when the batteries start to heat from 
overcharge.  No clue how your PowerEx works.  Web page links?

I personally would have put some lithium cells in it, but the charger MUST 
be one designed for that chemistry else they will be ruined or possibly 
even explode.

NiCads are a PIMA, but their relatively low self-discharge compared to some 
of the other, higher energy density batteries can be a useful feature.

> I don't know a lot about electronics (I work in infectious diseases), so
> is there something I'm doing incorrectly based upon the above
> information? I would think the cells would maintain their charge for a
> few months, at least. But this is not the case.
> 
> Thanks for any help you can provide.
> 
> Tony
> 
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Cheers, Gene
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