> For the sake of argument, if the starter draws 200 amps and you have to
> crank the engine for 15 seconds (which is a pretty long time when you are
> cranking the engine) that equates to just under 1 amp-hour. If you are
> using up 1/4 of your battery's capacity starting the car I think
> you need a tune-up.
Well, noting that the rated 'locked rotor' current for an early TR starter
is 450 amps (and it will draw close to that trying to start an engine at 15F
with the recommended SAE 20 weight oil) ... what is the efficiency of a car
battery at 15F and 400 amps ?
I wrote up a big long-winded explanation of Peukert's equation and battery
efficiency vs temperature ... but it occurs to me that there's an easier way
:
CCA (Cold Crank Amps) is a (modern) measure of a battery's performance in
low-temperature starting conditions, it's defined as the number of amps that
a battery can deliver for 30 seconds (yes, 1/2 minute) at 32F. Battery
technology has improved a lot since the 70's, with correspondingly higher
CCA, but when CCA first came out, 400 CCA was a pretty big battery.
So if I'm right about the current draw, and it happened to have been a nice
warm night of only 32F ... two 15 second starts is *all* of a 400CCA
battery's capacity !
Randall
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