On Sunday, March 24, 2002 12:29 AM, europa-builder@ntlworld.com
[SMTP:europa-builder@ntlworld.com] wrote:
>
But you can't determine the state and/or charge of the battery
> just from the voltmeter.
Not so. Battery terminal voltage (prior to the charging circuit being
activated) gives a direct indication of the state of charge of a battery
(provided the battery has stood for some time without significant
charge/discharge). State of charge and capacity are two unrelated aspects
of course, and capacity declines irreversibly with age.
>
> Or a voltmeter. I haven't seen either on any of the vehicles I've had in
> the last 10 years. >
Probably because most drivers didn't know how to use them!
> The max. reading will be limited by the regulator on the alternator and
I'd
> expect the voltage to be low to start with (i.e. after starting the
engine)
> and go up as the battery charges. But the rate of charge will depend on
> lots of things including the weather (temp. of the battery/how much
charge
> was used to start the engine (more in colder weather)), engine speed,
> avionics/lights load. I wouldn't expect to see a higher voltage if a
lead
> came free than I would if the battery was fully charged. Regularly
> monitoring the voltmeter as the battery charges will show a quick jump on
> the voltmeter if the battery has a mechanical failure, but the jump may
not
> be big enough to notice as the battery becomes fully charged.
Denied of the swamping and stabilising capacity of a battery, alternator
output voltage is likely to increase and/or become erratic. Without a
voltmeter, the first indication could be all the avionics frying! Rotax
tell us not to run the charging circuit with the battery disconnected.
Hope this isn't turning into another "tailplane pins" debate!
Duncan McFadyean
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