Re: [NTLK] deepToast battery

From: Andrei Chichak <>
Date: Tue Jul 17 2007 - 02:43:50 EDT

\> I started to wonder if the problem could have something to do with
> the recent spate of 100+ degree weather.

The general idea of a fast charging circuit is to charge the battery
at a higher than normal rate until the battery pack gives an
indication that it is charged.

With a NiMH battery, the indication is a quick increase in
temperature. The temperature is measured by the pack's internal
thermistor (a resistor that changes its resistance with temperature).

A typical cut off temperature for fast charging is 33C. which is, I
dunno, 92F or something like that? If the ambient temperature is 100F
which is about 38C, the pack is charged. But wait, it took almost no
time to go from first insertion to thermal trip, this pack is screwed.

Put your Newton with the battery and with the charger attached into
your refrigerator for about an hour (+5C which is a nice spring day
around here) and then plug it in to start the charge on a cold
thermistor. Take it out before about 8 hours.

Putting a pack into a freezer freezes the thermistor and gives you a
little while before charge+ambient > trip.


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Received on Tue Jul 17 02:44:02 2007

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