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From: jmuchow@SPAMMENOTcamlight.com (John Muchow)
Subject: Re: Reducing contact resistance for low volt use?
Date: Wed, 08 Jan 2003 08:59:04 GMT
Organization: MindSpring Enterprises
References: <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com>
X-Server-Date: 8 Jan 2003 09:01:12 GMT
X-Newsreader: Forte Free Agent 1.21/32.243
>>> Find the shorter, stub or even button sized cells. Less than half
>>>the weight, same voltage. If time is a factor, and there is little of
>>>it, a smaller parallel array might be better than the bigger seriesed
>>>array. Maintaining voltage guarantees that the current will be up
>>>there. Dead shorted paralleled packs would certainly drop down in
>>>voltage less than the series string. That math is easy.
Just about every cell in existence has been tested or used and only a
few provide the necessary discharge current. The smaller cells often
has much higher internal resistance that will exceed the benefit
provided by additional paralleled cells.
Good theory, but the technology hasn't caught up to it for our
>>>> Most builders are within ounces of their weight limitations for
>>> Sounds like some paring is in order in other areas. :-]
That's the big problem. They're at their weight limit *after* all the
paring down (drilling out the frame, reducing the amount of armor,
taking out a formerly-paralleled string of cells, etc).
Weight is much more of a concern than I can describe here. Just about
every builder thinks they can get a bot together that comes in
underweight. Some do, but their bots are usually immediately
destroyed or fail due to components not being beefy enough.
>>> There are single arm hold down clamps that clamp downward toward a
>>>flat base, similar to those used by glaziers in the glass industry.
We're planning to use a toggle-clamp and a spring-loaded stop to hold
the cell (horizontally) between them. The clamp would be placed so
that the stop would just about bottom out when the clamp lever was
lowered. We can get stops with springs rated from 2-40lbs.
>>> One could position the battery in a slightly or fully sunken well
>>>milled into a block of delrin or teflon or G10 or even aluminum (Hey,
>>>no more vault needed!). The bottom contact could be the aluminum
>>>block. The top contact would be positioned on the underside of the
>>>clamping device. At high clamping pressures, the worst that would
>>>happen at very high surge values would be a welding of the wire or
>>>contact to the battery. Parallel up clamps on a plank for a
>>>pre-assembly array tester.
Interesting idea! A lot of NiCd and NiMH cells have curved contacts
though...always a problem and one reason that pogo pins were
considered or something like 1/0 cable, end on.
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