Message text written by "Randall Young"
>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 !
<
CCA rating means that after 30 seconds of current at that current the
battery can no longer provide that level of current at the specified
voltage (probably 8 volts). That doesn't mean the battery is fully
discharged and will require the full 40 A-H to recharge. It mearly means
the voltage drops off to the limit voltage. While this is an important
parameter for starting the car, it doesn't mean the battery is discharged.
The laws concerning the conservation of energy say that if you put 2 A-H
into the starter and it cost you 20 A-H of battery charge means the other
18 A-H went somewhere. If it all went into internal battery heating the
thing would be boiling over after the 30 seconds were up.
The CCA is more a measure of ESR (effective Series Resistance) which is a
function of the mobility of Ions in the electrolyte and the conversion rate
at the plates than a reduction of the charge capacity of the battery.
Dave
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