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From: "Alan Melia"
Subject: Re: Reducing contact resistance for low volt use?
Date: Wed, 11 Dec 2002 11:45:56 +0000 (UTC)
Organization: BT Openworld
NNTP-Posting-Date: Wed, 11 Dec 2002 11:45:56 +0000 (UTC)
X-Newsreader: Microsoft Outlook Express 5.50.4522.1200
I may be wrong here but the physics says anything you put inthe gap will
make it worse! You need to consider a four terminal measurement .....i.e
you have a pair of contacts for discharging and a a pair in parallel
connecting direct to the battery terminal for measuring the cell voltage.
Then contact resistance at the current connection is not not part of the
measuring circuit. This could be a bit fiddly with C and D cells but is not
impossible..... the measuring contacts do not need to be big, as only small
currents are pasing through them.
"John Muchow" wrote in message
> I've been moving forward with designing a constant-current battery
> discharger (thanks to a lot of help from this group) but realized that
> I'm going to run into problems unless I can reduce the resistance
> between the contacts of the discharger and the battery cell terminals.
> One of the discharger's functions is to discharge individual NiCd and
> NiMH cells at levels from 0.25A to 100A (and feed voltages to data
> logging software for plotting). Keeping the resistance of the
> discharger low enough to get 100A from a 1.2V cell is one heck of a
> I don't think that merely pressing spring loaded (or screw-tightened)
> metal contacts against the cell terminals will work well enough. And
> soldering 4AWG wire to each cell being tested is a huge PITA (and can
> easily fry the cell if not done properly).
> I was wondering if an electrically conductive compound might be the
> solution? I've seen silver-filled conductive epoxies, but not a
> "grease" or similar non-adhesive compound.
> Does anyone have any conductive compound recommendations or ideas as
> to how I might be able to reduce the resistance between the discharger
> contacts and the battery terminals?
> John Muchow
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