On Sat, 03 May 2008 08:39:54 -0700, Bill Jeffrey
<wjeffreyAT@[EMAIL PROTECTED]
> wrote:
>Gentlemen -
>
>Thank you for your replies. I'm digesting them, and will let you know if
>anything develops.
>
>Colin - no I can't be not sure if the stated RPM figure is for engine
>RPM or alternator spindle RPM. I assumed it was engine RPM, for a couple
>reasons. First, max cited speed is 6000 RPM. This is more-or-less red
>line for the engine, so it makes sense to have a spec there. If it meant
>alternator RPM, that would be only 2000 RPM (engine), which is only low
>cruise speed. However, I do note that 6000 RPM (engine) means 18,000 RPM
>for the alternator, which seems kinda high for a mass-produced commodity
>metal item. Bottom line, I don't know.
All the alternators I've taken an interest in (which isn't all that
many to be honest) have been specced in alternator RPM. It makes sense
since that makes it independent of the pulley ratio. 18000 RPM seems a
lot compared to the engine, but there's no pistons or anything so it's
all just rotation. The 9-3 definitely has a roughly 2.8:1 pulley
ratio, so its alternator really does get close to 18000 RPM on the red
line.
>
>I would love to fit a higher-capacity alternator, but space is at a
>premium in that area. I'm not at all sure that I could wedge a
>physically-larger unit in there. I was hoping someone had done so, and I
>could leech on that knowledge.
The more I think about it, the more I think this can't possibly be bad
design. Even in th 80s, no-one would have accepted a car with a
charging system anywhere near as bad as you describe. Therefore yours
must just have a fault and it doesn't need a different alternator,
just a working one (or working wiring).
Getting it tested off the car would be my next step, or put your
electrical engineering skills to good use and make an alternator
ammeter. A cheap multimeter, set to 200mV and wired across the main
output cable should do. You'll need experiment to work out a
multiplication factor to make the readings meaningful, but it should
easily get you a semi-accurate idea of how many amps the thing can
manage before the voltage starts to drop.
Cheers,
Colin.
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