> 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.
Sorry, but I can't agree with that. If the battery has a high internal
resistance, it is still capable of giving a high voltage.
> > 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.
That being the case, Rotax should sort their regulator circuit out. The
whole idea of a regulator is to regulate. I presume by "swamping" you mean
load? With the battery removed, there will still be a load (ignition, fuel
pump, avaionics). If the regulator is working correctly I can't see that the
erratic voltage will be noticable except on a digital reading, then it may
only be 0.1V which you can expect anyway.
> Hope this isn't turning into another "tailplane pins" debate!
Cheers,
Mark.
________________________________
Mark Jackson - +44 (0)7050 645590
europa-builder@ntlworld.com
http://harley.pcl.ox.ac.uk/~mark/Europa
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