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From: Roger Johansson
Subject: Re: Reducing contact resistance for low volt use?
Date: Thu, 12 Dec 2002 23:04:54 +0100
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jmuchow@SPAMMENOTcamlight.com (John Muchow) wrote:
>Here's a 30-amp discharge curve:
I have watched robot wars on tv and it is interesting to see the
specifications you work with. Thanks for the data.
I doubt that you will need a zero resistance tester, the circuit from
John Fields should suffice for your needs.
The process is so slow so I guess you can do the data logging
manually, I guess that is how you do it.
It you need even lower resistance loads you could consider a purely
mechanical discharger, without Mosfets and wiring details.
You could simply short the battery with a hefty bar of copper, and
record the voltage manually every 10-20 seconds or so.
That would lower the load resistance to very low values.
Choose the dimensions of the copper (silver) bar so you get the
milliohm resistance you need.
Use a mechanical switch like pressing a u-shaped copper bar against
the battery poles with a mechanical lever system, lockable.
You probably have no real need for many different resistance values or
for keeping the Amp value constant.
You could keep it simple.
Just compare batteries by discharging through a known low resistance.
Record the voltage over the discharge time period.
The Amp value is easy to know from the cell voltage if you use copper
u-bars of exactly 10mOhm or 5mOhm or even lower if needed.
This mechanical method needs no electronics circuits.
Only a voltmeter.
Using batteries in series is acceptable if you can assume that the
cells are fairly similar, but if you short the battery with a hefty
copper bar, no mosfets, there is probably no need for that method.
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