Get an AL129X 115 amp alternator from eeuroparts.com or any local supplier.
It fits; I know because I have one in my 86 900. Also, you can install an
adjustable voltage regulator on your existing alternator. Try:
http://davebarton.com/AdjustableVoltage.html
Which would be considerably cheaper if it works. (I have not tried this.)
Don Kirkpatrick
Also an electrical engineer
"Bill Jeffrey" <wjeffreyAT@[EMAIL PROTECTED]
> wrote in message
news:OVtSj.108530$497.38703@[EMAIL PROTECTED]
> 1993 900S turbo convertible (USA)
>
> Simple question, but complicated lead-in, so that you may understand
where
> I have been. Let me open by saying that I am electrical engineer.
>
> I have had 3 Saab 900's, all of the same vintage. Only the one above is
> left. I love these vehicles, but they all have shared one problem - they
> eat batteries. On each of them, the day comes, repeatedly, and sooner
> rather than later, that when I go to start it, the battery is flat for
no
> apparent reason. I've done all the standard stuff - checked the grounds,
> checked the connections throughout, maintained the batteries properly,
> looked for intermittent parasitic drains (stuck switch, etc). I replaced
> the voltage regulator with a new Bosch unit. I checked the alternator
> terminal voltages in accordance with Bentley. No apparent problems, and
no
> fixes. As a desperation measure, I ran separate wires (#10) directly
from
> the alternator output terminals to the battery terminals, and that
helped.
> But not enough.
>
> Recently, the thing stranded my wife. Again. And I got the ultimatum.
Fix
> it or sell it. So I got more seriously interested in what's going on.
> Instead of spot checks, I attached a permanent voltmeter to the cig
> lighter circuit, and drove it for several days. And lo and behold, the
> problem quickly became obvious. The alternator is inadequate to the
task!
>
> With the air conditioning off, and no big drains (engine cold so
radiator
> fans off, power windows/seats quiet), the voltage stays well up, in the
> range of 13.8-14.0 volts. But as soon as a big drain shows up, the
voltage
> drops to the 12.5 region, and that is not enough to maintain a battery.
>
> 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
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