Charging Problems

[67SWT]

The alternator light on my 72E is currently on all the time.
The alternator/regulator is Motorola SEV 14V
I have the following reading at the battery.

13.1 Volts when the car is not running.

12.8 Volts when the car is running at 1000 RPMS, 2000 RPMS, or 3000 RPMS
12.5 under the same condition with the headlights on.

Electrical problems tend to be my nemesis. I know that probably more information may be needed but does this point to an alternator issue, regulator issue or both?

If so any recommendations of shops that service these.

Thanks

[M_deJong]

Light is on bright, doesn't dim or change with RPM? I would say you have a strong battery but no alternator function with those voltage readings.

Pelican and Zims sell rebuilt alternators but I have had good luck have local shop rebuild the Motorola units for less money. I did one myself too. Its usually just a bad diode. Typically a shop will replace bad diodes, replace bearings, turn the rotor and contact rings, and maybe replace brushes and internal lead wires if they are toasty. A local independent Porsche mechanic would be a good person to ask for a shop recommendation.

R&R of the alternator is a pain but not that difficult. Make sure you disconnect the battery before you start.

[67SWT]

Mike
Thanks for the reply, I have the alternator out will try and find a shop to rebuild it. Unfortunately not much in the way of help locally.

[M_deJong]

Since you have it out, there are a couple of quick diagnostics you can run. Remove the brush holder (2 cheese head screws) and check the condition of the brushes. You can also check their resistance. One should have low resistance to the terminal, the other to ground. Also check the armature resistance. Remove the isolation diode bridge (big red thing) and check the isolation diodes and then the main diodes wiith a ohmmeter. For the main rectifier diodes you should see low resistance across the D+ and D- terminals in one direction, and very high resistance the other direction (reversing the leads of the ohmmeter). My guess is you have an shorted diode and will see low resistance both ways. If you have a digital voltmeter with a diode check function that is even better. I'll send you a PM with shop recommendations.