Alternator Light On

soulful66 · Post by **soulful66** » Sat Oct 27, 2007 8:26 am

Last week my alternator light flickered on while driving. I pulled over and checked my battery/starter connections. They were good, and the light went out when I revved the engine.

Yesterday I went out and the light was on and it would not go out by revving the engine. Luckily a co-worker lives down the road and he gave me a lift to work.

That night I checked my battery voltage. The starting battery and aux battery had 12.80 vdc. The alternator was rebuilt last year and has about 500 miles on it. I swapped the volt regulator with no effect on the light.

Anyone know any other things to check?
Best Regards,
John

soulful66 · Post by **soulful66** » Sat Oct 27, 2007 9:15 am

Ok, I went old school and checked for a magnetic pull from the alternator pulley. No pull, so the alternator must be bad.

I am going to test the voltage at the regulator to see if there is a problem with the regulator not exciting the alternator's field windings.
Best Regards,
John

dingo · Post by **dingo** » Sat Oct 27, 2007 10:28 am

To check the alternator without voltage regulator:

With the fat red wire hooked up to the battery (or starter bolt), unplug the wiring harness from the voltage regulator, jump the green wire to 12V and start the engine. This tells the alternator to deliver full capacity current to the battery. You should see ~13.8V at the battery. If this works and you are not getting the 13.8V when the harness is hooked to the voltage regulator as normal, then point fingers at the regulator. If it doesn't work, then you know your alternator is bad.

(from Type 2.com)

soulful66 · Post by **soulful66** » Sat Oct 27, 2007 11:36 am

Dingo, thanks brother! I will give 'er a try.
Best Regards,
John

Post by **Amskeptic** » Sat Oct 27, 2007 6:35 pm

soulful66 wrote:Dingo, thanks brother! I will give 'er a try.
Best Regards,
John

Let us know. . . . . . we're waiting right here.
Colin

soulful66 · Post by **soulful66** » Tue Oct 30, 2007 5:29 pm

Ok, it is the alternator. I am going to wait until next year's IAC visit when an engine rebuild is planned. I have a spare alternator now, but it is getting to cold lately. Well, I will probably get to it sooner... who am I kidding! Thanks for the help!
Best Regards,
John

dingo · Post by **dingo** » Tue Oct 30, 2007 7:24 pm

If you are looking for an afternoon project, pull the alternator and take it apart. It might just need new brushes or light sandpaper on the commutator. It's quite do-able.

soulful66 · Post by **soulful66** » Wed Oct 31, 2007 2:53 pm

That sounds like a good project. I have brushes on hand, so that is nice. Perhaps on the next warm day...if there are any left here.
Best Regards,
John

Post by **Amskeptic** » Wed Oct 31, 2007 4:13 pm

soulful66 wrote:That sounds like a good project. I have brushes on hand, so that is nice. Perhaps on the next warm day...if there are any left here.
Best Regards,
John

John, open the door to the house, crank the heat up, then bring the alternator into the kitchen. Shut the door behind you, turn down the heat to where it was. Jeanne told me to tell you you're allowed.

twinfalls · Post by **twinfalls** » Wed Nov 21, 2007 12:03 pm

soulful66 wrote:That sounds like a good project. I have brushes on hand, so that is nice. Perhaps on the next warm day...if there are any left here.
Best Regards,
John

You need a big fat soldering iron to disconnect windings at diodes. 6 big diodes and 3 smaller ones.
Then you can check with an ohmmeter for each winding continuity ( cut wire ) and isolation ( wire shorted to body ).
The most likely culprits are diodes
Diodes, free from the windings can each be checked with a diode meter or
an ohmmeter ( check for a high and a low resistance swapping the probes....a bad diode reads open circuit or shorted on both settings ).
There is no commutator ( this belongs to dynamo generators ). There are 2 brushes riding on 2 rings to feed the rotating winding.

I spent a full night on a Golf Rabbit alternator to find nothing wrong in the alternator itself. The regulator was bad.

Post by **Amskeptic** » Wed Nov 21, 2007 12:12 pm

twinfalls wrote:You need a big fat soldering iron to disconnect windings at diodes. 6 big diodes and 3 smaller ones.
Then you can check with an ohmmeter for each winding continuity ( cut wire ) and isolation ( wire shorted to body ).
The most likely culprits are diodes
Diodes, free from the windings can each be checked with a diode meter or
an ohmmeter ( check for a high and a low resistance swapping the probes....a bad diode reads open circuit or shorted on both settings ).
There is no commutator ( this belongs to dynamo generators ). There are 2 brushes riding on 2 rings to feed the rotating winding.

I spent a full night on a Golf Rabbit alternator to find nothing wrong in the alternator itself. The regulator was bad.

Good stuff here.
Colin
(so where do we get the correct diodes?)

twinfalls · Post by **twinfalls** » Wed Nov 21, 2007 1:07 pm

Amskeptic wrote: (so where do we get the correct diodes?)

Sorry, I know no source for the big diodes. I suspect their rating is huge, like 100 Amps. Hobby electronic shops don't carry that big, and their prices are outrageous.
I guess, junk alternators can be a source, not all diodes are dead. May be one can extract and replace diodes from their holder acting as a heat sink.
I am quite sure, the auto industry is using the very same power diode all over the world, mass produced, cheap for the guy buying by the 10 thousands.

There must be a source, because shops revamp, failed alternators.
I see their prices are reasonable.

twinfalls · Post by **twinfalls** » Wed Nov 21, 2007 1:13 pm

I FORGOT....
If you go soldering / un soldering a winding at a diode with that big Mamma soldering iron....
Heat is a diode killer.
Clamp the diode lead with a plier that will divert the heat.

Post by **Amskeptic** » Wed Nov 21, 2007 1:17 pm

twinfalls wrote:Clamp the diode lead with a plier that will divert the heat.

I use Thermal Mastic, a heat-absorbing paste. Great stuff. Available at HVAC stores where those poor saps, of whom I once was one, had to buy the stuff so they could braze compressor fittings without burning down the house.
Colin

Itinerant Air-Cooled

Itinerant Air-Cooled

Alternator Light On

Alternator Light On