Subject: Re: Questions on building a battery charger
Date: Mon, 25 Nov 2002 20:16:00 +0000 (UTC)
NNTP-Posting-Date: Mon, 25 Nov 2002 20:16:00 +0000 (UTC)
User-Agent: tin/1.5.14-20020926 ("Soil") (UNIX) (Linux/2.4.19 (i686))
Robert Richter wrote:
> I am building my own battery charger with a MAX712. (Probably seen
> this post many times) I am wondering what the charge efficiency of a
> NiMH battery is if I use the slowest charge time-out available on a
> MAX712 IC (the slowest time-out is 264 minutes). I would like to
> match my amp-hours of the batteries with this safety timeout with a
> comfortable margin for determining my sense resistor, or in other
> words, the charging current. The batteries are typical AA 1600mAH
> Is it better on the crystals of NiMH batteries to use the slowest
> charge rate or a faster charge rate, such as one hour? Speed is not
> as much of an issue to me as I want the charger to be "intelligent."
> The original charger was a trickle-charger that slowly cooked the
> batteries, so I want something a little better.
You can't really cook NiMH cells with a slow-charger, they may very slightly
be reduced in capacity after months on charge, but that's about it.
Slower charges are generally better, though not once you get much past C/50.
Assuming the MAX712 has delta-vee shutoff, then if charging at a four
hour rate, C*.35 sounds about right for getting them fully charged.
As in future you may want to use larger cells as they come on the market,
I'd consider 2C to be a reasonable "safe" figure, which would translate
to about 3200mAH, or about 20000mAm, so a charge current of about 760ma,
which would mean that a dead cell would terminate charging in about 177
It would be a good idea to spend a little while reading various makers
http://inquisitor.i.am/ | mailto:email@example.com | Ian Stirling.
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