NNTP-Posting-Date: Mon, 25 Nov 2002 23:01:10 -0600
From: "Dave VanHorn"
Subject: Re: Questions on building a battery charger
Date: Tue, 26 Nov 2002 00:01:35 -0500
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. The unit would be modified
> so the adapter plug went directly to the battery. I also need to know
> where to buy AA batteries with welded on tabs.
Your local batteries plus will weld up any pack you like, if you buy the
cells from them.
> I am capable of taking 1600mAH and dividing by charge time to get
> current, but my question was, "what is the efficiency of NiMH when
I've not seen a figure on this that I'd call solid. I'd say 120% is about
right, but it will vary with charge speed, lower at high rates.
> As far as the Atmel Tiny-26, I am building a one-of-a-kind unit, so
> assembly language for just one product is not feasible--not to mention
> that I don't have a programmer or assembler for this chip.
www.atmel.com Studio 3.5 is free, and is your assembler and simulator.
FBPRG16 is a freeware programmer, needs six wires off your parallel port.
> I am not trying to go into mass production, but simply building a one-of-a
> unit. The application is one where removal of the batteries is not an
I hear ya. :)
The 712 isn't bad, except for the high trickle current.
If you can figure a way to cut that down, you're home free.
It's a bit clunky, but maybe a FET that's turned on when you have input
power, that drains off most of the trickle charge through a resistor?
> As far as C/300, some people on the web say C/10 doesn't hurt anything
> no matter how long it is left on the charger, and others think that
> any over charge slowly ruins the battery.
C/10 is fine for NICADs, but it will push NIMH batteries into charge
C/300 is where you want to be. See McGraw Hill=s handbook of batteries.
> Is it a problem to use the
> trickle charge current of the '712 if the unit is used during the day
> and plugged in each night to be topped off?
You might get away with it.