On Thu, 01 May 2008 18:14:25 -0700, Bill Jeffrey
<wjeffreyAT@[EMAIL PROTECTED]
> wrote:
>1993 900S turbo convertible (USA)
>
>So I checked the alternator specs in Bentley. The "80 amp alternator"
>puts out 80 amps only when the engine is screaming at 6000 RPM! And I
>don't drive that way (that's why I still have a 1993 Saab!) At 2000 RPM,
>it is spec'ed to put out only 54 amps. And below 1900 RPM, the output is
>essentially zero. And that is pretty pitiful against the requirements of
>the electric radiator fans and the air conditioner clutch. In these
>conditions, I can actually see the voltage drop and rise as the
>directional signals flash. And Lord knows what happens if I turn on the
>headlights.
>
>So. Now I know what is happening. The alternator cannot put out
>sufficient current to sup****t all the goodies that Saab has installed.
>And thus the final question (thanks for your patience) is whether there
>is a way to increase the alternator output at low RPM - OR - is there an
>aftermarket alternator that will put out a bit more current at low RPM,
>without making major mechanical mods to the alternator mounting system.
>
>Bill
Are you sure the RPM figures you've found are for engine RPM and not
alternator RPM? There's normally some gearing done on the pulleys.
It's about 2.8:1 on my 2001 9-3. 2000 alternator RPM is well below the
engine idle speed.
It certainly sounds wrong that you can't maintain a charge with the
engine running though. The 9-3 happily manages 14.4V at idle with
headlights, foglights, HRW and seat heaters all on. You could get the
alternator tested off the car if you take it to an auto electrical
specialist. If it really is bad design, you could try fitting a
smaller alternator pulley, but be careful that the alternator won't
get over-speeded at max engine revs. Do you know what the pulley ratio
is on the 900?
The other way would be to fit a higher capacity alternator from a
different model - they do tend to work better all the way down to low
revs. Check pulley ratios again though. Bigger alternators are often
intended to run faster.
Cheers,
Colin.
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