Chris,
Just got back from a nice three-day mountain retreat weekend and found my
Tiger list inbox overflowing with good stuff. I guess I better get on this
particular one right away, although it's already evolved into "can you top
this winter experience from hell". Somehow, I don't think 850 cold cranking
amps really means you can draw 850 amperes. I think when you engage the
starter, the voltage drops a lot; like down to 9V or so; hence the ballast
resistor which is bypassed on starting. The rate at which you can pull
current is the limiting factor when the battery is cold, not stored energy.
But more stored energy is what you get in the bargain when you increase the
plate area to lower the resistance. So bigger is better - in this case as
in a few others. Turn on the lights, short it out with battery cables, or
just crank a few seconds longer. What''s the difference? Either way, the
current is going to warm up the battery. And the heat is dissipated mainly
just where the resistance is highest, which if it's at the
plate/electrolyte interface, is just where you need it most. Now, where's
that old Physics 101 text I used to have. ;-)
Bob
At 03:26 PM 1/17/00 -0500, Chris Thompson wrote:
>Robert Palmer must be off today. I fully expect we'll get a dissertation
>on this, but I recall doing the calculations in Physics 101 twenty some
>years ago showing that the heat generated by turning on the lights prior
>to starting (and then turning them off when starting) had net positive effect.
>
>Since this was Physics 101, I'm sure there were numerous simplifying
>assumptions. But the Professor swore that it worked.....
>
>Chris Thompson
>Executive Vice President
>Recognition Research, Inc.
>1750 Kraft Dr. Suite 2000
>Blacksburg, VA 24060
>540.961.6500
>540.961.3568/fax
>cthompson@rrinc.com
>www.rrinc.com
>B382000331
Robert L. Palmer
UCSD, Dept. of AMES
619-822-1037 (o)
760-599-9927 (h)
rpalmer@ucsd.edu
rpalmer@cts.com
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