smithk993

Two months ago my alternator was showing signs of going bad so I had it rebuilt by the shop the Porsche dealer uses. I did the R&R on the alternator. All was well for two months.

Yesterday I stalled the car taking off on a steep hill and quickly restarted the car. The battery warning indicator came on and the voltage gauge showed less than 12 volts. Got it home and let it sit overnight.

This morning I put a external meter on the battery and it showed 12.2v. I then started it and the meter showed 13.8. Let the car run for 30 minutes and all showed OK. I then stopped and started it a couple of times and on the fourth or fifth start, same thing, meter showed 11.4-11.8 volts. Stayed that way for couple of minutes. Shut it down and started up again and back to normal. I did this several times and every once in a while it will act like not charging and the next time, back to normal.

I really hate to R&R the alternator again as it's a bit of a pain but I don't trust the way it's acting. Could the rebuilt alternator have a problem this soon?

Any ideas of what could be causing this intermittent problem?

ca993twin

Sounds to me like the voltage regulator gone bad. Are these built into the alternators or are they a separate unit?

smithk993

I believe the VR is a separate unit that is on the back of the alternator. That was supposed to have been replaced as part of the rebuild. Unfortunately to get to it, the alternator has to come out.

Macster

Be sure the battery is ok. The failing alternator could have allowed the battery to run down and they do no like this.

Have the battery tested twice, once early in the day and again later to see if just sitting it lost power.

Only if you're sure the battery is ok then you can suspect the alternator.

Sincerely,

Macster.

smithk993

I talked with the shop which rebuilt the alternator and they asked if it was getting a control signal? Not sure what that means or how to test?

I do recall two connections on the back of the alternator, one heavy duty cable and the second a much smaller gauge.

Any thoughts on this control signal being the cause of intermittent failure after some starts?

Kevinmacd

The inputs are the field current supply and the control voltage input, and the output is the field current to the rotor. The regulator uses the control voltage input to control the amount of field current input that is allow to pass through to the rotor winding. If the battery voltage drops, the regulator senses this, by means of the connection to the battery, and allows more of the field current input to reach the rotor, which increases the magnetic field strength, which ultimately increases the voltage output of the alternator. Conversely, if the battery voltage goes up, less field current goes through the rotor windings, and the output voltage is reduced.