Bench-testing alternator

[ohecht]

My alternator is out of the car and has suffered a small fall onto the back of the unit.

I would like to test it, or at least verify the integrity of the connections, before reinstalling it.

Is there a way to do this? What tests and values should I look for among the connections if it is possible?

Thanks,

Olivier

[nostatic]

I know they can be bench tested, but I don't know the details. I can say that even a clean bench test doesn't mean that it is totally healthy...but it should be good for a work/no work answer.

[RoninLB]

Originally posted by ohecht
My alternator is out of the car and has suffered a small fall onto the back of the unit.

diodes are impact sensitive.. even a car crash may destroy a diode. I assume things haven't changed much in 30yrs concerning diodes. A quick diode check involved an ohm meter connected to alt output and the alt ground with wires disconnected from the car. I think the routine was less than 1k ohms for everything to be OK.. Sorry I haven't done the routine in years.. but any shop guy will know.....

[Lorenfb]

You really can't check the diodes that way. They are all (three at time)
connected basically in parallel because of the windings. Two of the
three could be bad and the resistance check would be O.K. The unit
really needs to be turned using a motor or a drill.

The D+ and B+ outputs need to be checked separately. Each is connected
to the DF and excited using a test light connected to 12 volts. Once
the alt. reaches about 600 rpms, the testlight will go out indicating
that all diodes are O.K. for that output (D+ or B+). If the light glows,
then a diode/diodes is/are bad.

Have Fun
Loren
'88 3.2

[911pcars]

To check diodes, you have to unsolder them to test them individually for one-way continuity.

A "bench test" at an electrical shop where they physically spin the alternator is probably a better suggestion.

Sherwood
http://members.rennlist.org/911pcars

[KNS]

Thanks guys, I'll find a proper shop.

[KNS]

Whoops! Responded to a seven year old thread.

[James Brown]

Take it to any shucks or napa and the'll check it out for free.

[James Brown]

Crap, me too!!

[RWebb]

never hurts to bump an informative thread

[James Brown]

Yes it will be asked again soon

[shbop]

..and a 944 pulley fits right on. jic

[86 911 Targa]

Originally Posted by 911pcars

to check diodes, you have to unsolder them to test them individually for one-way continuity.

A "bench test" at an electrical shop where they physically spin the alternator is probably a better suggestion.

Sherwood
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