Re: [NTLK] Recharging disposable AA batteries?

On Tue, Dec 12, 2006 at 12:48:43AM +0100, Frank Gruendel wrote:
> > http://www.afrotechmods.com/reallycheap/batteries/batts.htm
>
> > Anyone here who has a lot more knowledge than I do have any
> > comments?
>
> I don't know if I have "a lot" more knowledge than you, but
> given the fact that you are open to trying what is described
> on this page, I guess I have "some" more knowledge.

I've taken a quick look at the circuit given and wouldn't trust it
even to charge nicads. A few back-of-an-envelope sums show that
supplied by 12V and charging a single cell discharged to 1V the
transistor is dissipating 621mW. That's awfully close to the
2N3904's rating of 625mW, and allowing even 1% tolerance resistors
(salvaged components likely to be 5% or 10%) you have to say it's
over, to say nothing of variations in power supplies, temperature
etc.

If you really want to try recharging alkalines, a standard battery
charger is a better option than this. Just make sure it's trickle
charger (12-14 hour charge time or even longer) and don't blame me
if it goes wrong. Peak detection would be welcome too.

> If I were you, I'd buy four AA rechargeables and recharge them
> in an external charger. A coffin is very much more expensive
> than such a setup.

I agree. I've seen packs of four AA nicads (850mA if I remember)
going for a pound locally, which recharge with much less risk and
last a lot longer. Even 2500mA NiMH types don't cost more than
seven or eight pounds. Given those prices, IMHO you'd be a fool
to try anything else.

-- 
Andrew Smallshaw
andrews@sdf.lonestar.org
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