In a message dated 10/19/2009 1:51:09 PM Central Daylight Time,
tr3driver@ca.rr.com writes:
> The pulses aren't particularly high current, but are rather high voltage
> and
> very short. Normally, a sulfated battery won't take any current at all at
> normal charging voltage. Sometimes you can desulfate a car battery by
> just
> applying a high enough DC voltage to pass a little bit of current, and
> limiting the voltage/current. But the spikes supposedly work better, and
> will supposedly even improve a working battery.
>
> See for example the description at
> http://www3.telus.net/sail/sj23/e_electrical_tips/e04.html
>
This is a good description of the behavior of deep cycle batteries.
Another phenomenon common to cranking batteries is that of plate erosion. Car
batteries are optimized for Cold Cranking Amps. Typical Specmanship. CCR is
highly touted in battery advertising to the point of ridiculous. To get that
kind of cranking capability the plate area is maximized at the expense of
plate thickness. The plates are thinned to the point that a fiberglass mat
is used to support it. If a battery is discharged enough the lead is
completely removed from areas of the glass mat and recharging will not
redeposit
the lead where there is no plate anymore.
Modern cars are typically equipped with charging systems that will keep up
with all but the very worst case electrical load at all engine speeds. Our
cars were not so equipped and relied on the battery to subsidize the
charging system during engine idle periods. This was fine when batteries
typically
would tolerate this but today's batteries are more susceptible to over
discharging. The result is reduced current capabilities.
But the Cranking capabilities of batteries is so high that even when
degraded but 60 - 70% they still start our cars. So there is a compensation
action taking place.
Good thing we overcompensate on battery size.
Dave
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