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Subject: Re: Reducing contact resistance for low volt use?
Date: Wed, 11 Dec 2002 14:39:45 -0800
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Here's some data
I took number 6 solid copper wire and rounded the
slightly. Mashed a pair of them onto the negative
end of a D-Cell
NiCd. Shined up the end of the cell with a
pencil. I pushed hard. My springs run out of gas
at about 10
pounds, so total pressure was probably 20-30
Lowest resistance I could get was 0.8milliohms.
That's 0.4 milliohms/contact point. That doesn't
include any of the
wire or connection clamps. Multiple contacts
with independent springs should reduce the
Here's a picture of the jig.
With such low voltage margin for the load, you
to resort to using a hall-effect current probe in
feedback to set the current for a passive
load...well not passive,
just not using a KW of power to create the load.
More volts would help. Can you discharge two or
more at once, but
just measure across one cell? That would make the
load design a
What characteristic of the cell are you using to
determine it's health?
Could you use a pulse measurement? That would
help the heat problem
Might be interesting to put a cell on a curve
tracer and see if you can
John Muchow wrote:
> >>>Looking at a RatShack c-cell, it has a big shiny top contact that's
> >>>most of the overall diameter across (and has the small, regular
> >>>contact bump in the middle.) It should be easy to hit this with 50 or
> >>>so pogos on each end, plus one extra for a Kelvin contact.
> Hmm...I could solder them all to a hunk of copper or silver (stepped
> so the outer Pogos can reach the battery terminal) and then solder (or
> bolt/solder the connector) the 4AWG wire to the same piece to connect
> to the discharger.
> I wonder if that would be better than just having a stepped copper or
> silver plate contact that would press directly against the battery. I
> guess a lot depends on shape of each cell...gotta check that.
> John Muchow
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