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From: jmuchow@SPAMMENOTcamlight.com (John Muchow)
Subject: Re: Reducing contact resistance for low volt use?
Date: Tue, 07 Jan 2003 01:51:52 GMT
Organization: MindSpring Enterprises
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X-Server-Date: 7 Jan 2003 01:53:42 GMT
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>>>>1600mAH? Where did that come from? Most of the cells used in these
>>>>high-current applications are 2400-3600mAH. And in 20-30 cell
>>>>strings, they most certainly do deliver a LOT more than 100A.
>>> Not when they are in series, as you described. In order for a
>>>battery bank to scale UP in ampere hour rating, they have to be in
>>>parallel, not series. If series ed, they only exhibit the rating of a
>>>single cell, as what scales UP in a series battery pack is voltage,
>>>not current capacity. This rule does NOT vary. It is basic
But, for my constant-current discharger (which is what all my posts
were about), I probably need more than one cell in series to help
force more current through the circuit to help me get my desired 100A
And the 20-30 cell strings used in combat robots most certainly
deliver more than 100A. And that's only a single series string, no
cells in parallel. For the 'bots that require several hundred amps,
they'll parallel several strings together.
>>>>only discussed packs when mentioning these applications. We only want
>>>>to test individual cells though (for several obvious reasons).
>>> They won't need to be tested to the current levels you describe.
>>> You can test overall performance from one maker to another by
>>>logging data at a lower discharge rate.
>>>will show how well the battery will work in real world scenarios.
>>>A motor will not run if the voltage drops to zero. More batteries are
>>>needed, not your "better at working into a short" tests. It's like
>>>asking a car engine to run after dumping the clutch while up against a
>>>wall with the brakes on full.
Welcome to the world of combat robots. :-)
Your car scenario described above is probably the least damaging thing
these robots would do to themselves (yup, many run on internal
combustion engines too).
>>> If your battery packs are seriesed batteries to obtain higher
>>>voltages, then you need to place two or more battery packs in parallel
>>>to gain higher power handling ability. Looking for the brand that
>>>fights into a dead short the best is futile, in my view. You should
>>>concentrate on keeping the pack at voltage. That means more batteries
>>>(battery packs), in parallel.
We don't have that option...that's why we need to test a single cell
(or string of cells). Builders are *severely* limited by weight
limitations and will *never* run a component at their ratd capability.
If they can only afford (financially or due to weight restrictions)
one battery pack per motor (or for the entire 'bot), then they want to
know how long the battery pack will run the several over-volted motors
they're using. The fight only lasts 3 minutes.
We never wanted to test into a short, just into loads that allow 100A
to flow from the cells (absolute max.). Now, that's almost a short, I
agree, but it's what's encountered all the time with these robots.
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