How to bench test a 911 alternator

[gorskined]

Hello I was hoping someone could tell me what points off the back of the alternator I need to put a meter on to test for voltage I have a way of spinning it fast enough I just need to know which points to connect to

Thanks

[356RS]

Do you have a voltage regulator wired up with it?

[Trackrash]

A couple of things. What is the problem with the alternator?

You can test the diodes with a multimeter.

You can test the continuity of the windings and check to make sure none are shorted to the frame or rotor.

After that you would need to test under a load to make sure it can output enough to charge the battery and run stuff on the car. What do you plan? Spinning the battery with an electirc drill when it is hooked up to a regulator and battery? Some guys on youtube are doing that.

[Trackrash]

If you post a picture of your alternator it will help.

[Richey]

A crude test : connect DF and D- to a 12 volt battery and spin , measure the voltage at B+

[stubble88]

Which one is Df? Is it this one I’m pointing to?

[E Sully]

Connecting voltage to Df won't work. Your alternator has an internal voltage regulator. No access to Df. The initial power to the alternator Df is from blue wire D+ in diagram. This is why the indicator bulb lights when the alternator is static, and goes out when the alternator output exceeds battery voltage.
Alternator with external regulator.


Alternator with internal regulator.


Check out this video. A meter will show your voltage output. Should be between 13.5-14.5. Any higher will cook the battery.
https://youtu.be/R0W6LX60brU?si=Hv0vGQgZU2lAdSIx

This Technical bulletin mentions why the wattage of the indicator lamp can matter.