Alternator Checkup

Alternator Checkup

>I've noticed that my voltage gauge drops as the car warms up
>and as I turn on more accessories. Battery is good.
>I suspect the alternator is worn out. What do I check?

If you have the Bosch alternator, one thing to check is the voltage regulator. It is mounted on the back of the alternator, held in with two screws. Pull it off and check that the brushes are not worn out. (0.02 inch minimum lenght springs to mind, although I was not able to find the spec. in the workshop manuals.) If the brushes are ok, then look carefully at the front side of the regulator (the side with the brushes), and you should see a metal contact/brush/pickup. This is a ground strap. Polish it up, as it tends to get quite covered with carbon and road dirt. Try to find it's mating half inside the alternator body and clean it also. This is a weak point for the Bosch alternator, but a really cheap problem to fix; just cleaning the contacts on the ground strap.

If that does not improve your situation any, you can do what I did and double the wiring harness from the alternator to the jumper post with a good ten gauge wire. The wiring harness seems to build up resistance with age.

BTW, it is normal to have a higher charging voltage after you first start the car, as the differential between your alternator and battery is greater. As the battery charges, this differential lessens, and it appears that the alternator is no longer putting out the correct current, but it is just that there is less need for high charging rates. (Think of how the meter on a charger works... high readings for a discharged battery, low or no readings for a fully charged battery.

I hope this helps somewhat...

J.B. Lisankis
1981 928 S Euro Spec. 5 Spd

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