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From: email@example.com (Robert Richter)
Subject: Re: Questions on building a battery charger
Date: 26 Nov 2002 08:58:43 -0800
NNTP-Posting-Date: 26 Nov 2002 16:58:43 GMT
- Ren - wrote in message news:...
> On 25 Nov 2002 10:07:51 -0800, firstname.lastname@example.org (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 will get many wise & correct answers to this question, so let me
> present you with a tangent:
> Use a simple "resistor in series" type C/10 charger, and buy some
> extra battery sets. As modern frequently used batteries have a life
> cycle that does usually not exceed ~ 3 years anyway, why investing in
> hi-tec charger technology if the return is marginal.
> Sets of 4 AA NiMH are < $10 nowadays. I have 3 such sets for my
> digicam which I abuse all over the place (ovecharging in el cheapo
> wall charger), and all of them reached the 2 year mark with flying
> colors. And always a fully charged set when I want it as I keep
> topping off packs regardless of discharge state. Poor techinical
> practice perhaps - but the cells don't seem to mind.
The reason I want to be "nice" to my batteries is the inconvenience of
replacing them. For my digital camera or my PDA, I would probably
never recover the expense of a smart charger over an "abusive timed
charger". However, here, the original batteries must have the epoxy
ground out; I need to buy new batteries with solderable tabs; and then
I must epoxy the new batteries back in (without blocking the vents, of
course). I don't want to do this every two years, so I feel that if a
$7.00 integrated circuit already does smart charging, and all I do is
add a transistor and a few resistors and capacitors, this is the route
I want to go.
Another angle to look at along your line of thinking--will this GPS be
obsolete in another two years anyway?
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