At 6:42 AM +1000 18/2/98, JAMES_S_WALLACE@HP-Canada-om1.om.hp.com wrote:
> From time to time, a discussion comes up about how not to overcharge a
> battery that's in storage. This got me wondering: why don't they
> overcharge while they're in use in the car?
>
> Which leads to: Why not build a battery charger that replicates the
> car's charging system? One could just use a transformer and rectifier
> (this would be like the alternator and rectifier), followed by a
> voltage regulator from a car. It seems to me that it would look the
> same to the battery.
>
> Why not? Any (constructive) comments?
>
> Please respond in terms of electrons rather than molecules if
> possible, as I'm chemically-challenged but electronically-oriented.
>
> Thanks,
> Jim Wallace
In theory, if the battery is held at its nominal charging voltage (ie 14.6
Volt) continuously, no damage should occur. Problems arise because the
battery may not behave exactly according to theory and the voltage control
on the charger may not be entirely accurate. With a high capacity charger
and a continuous connection, serious overcharging could occur.
A typical battery would have a capacity of 50 to 100 Amphours and batteries
can usually handle a continuous charge at their 100 hour discharge rate
(the current which would discharge the battery in 100 hours) without damage.
I would recommend a very low capacity (trickle) charger that can deliver
0.5 to 1.0 Amp and/or run it non-continuously. This should be sufficient
to keep the battery charged without subjecting it to any damaging stress.
If you have a typical 4 Amp charger, try running it for 3 to 6 hours a day
by using an electrical timer or connecting it via a lamp which is switched
on for a few hours a day (suggestions have been made on this list
previously about connecting it to the garage door light).
Regards, Trevor Jordan
74 TR6 CF29281U
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