In a message dated 10/13/2006 9:05:34 PM Central Standard Time,
tr3driver@comcast.net writes:
> I went through this many years ago ... the stock TR3A generator was rated
> at 19
> amps (although most cars will have the later 21 amp unit). I measured the
> total
> load, driving in the winter with the headlights, heater &wipers on; at 24
> amps
> !
>
Batteries are much different than the batteries we had "back in the day."
When these cars were young the thinking was that if you drive at night and all
the loads result in a 10 or 15% total net discharge on the battery but then
drive the next day the the generator can replenish the charge, no big deal.
The
overall cumulative result is the sytem works.
But today automotive cranking batteries are over-optimized for Cold Cranking
Amp ratings (it is a major selling point) and this is accomplished by
maximizing the plate area. But to do so without using much more lead than
before they
make the plates thinner. With thinner plates it takes less % discharge to
etch away whole areas of the plate surface during a discharge and when
recharging that area is not restored resulting in less plate area and less CCA.
This
is not a problem for modern cars that are much better at maintaining the charge
state of the battery at 100%. But our old charging systems were designed
around batteries that were more tolerant of this type of abuse.
Perhaps a better choice of battery for an early TR with a traditional
charging system is a deep cycle battery. But these cost more. All a function
of
market volume.
Dave
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