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Yesterday volt meter, on start up was reading and fluctuating between 16-19 volts.
Ran vehicle for perhaps 1-2 minutes and decided I didn't like it.
Opened hood, the exterior of the alternator was hot, but both bearings end were cold, it wasn't bearing friction.
Started up vehicle and volts flatlined to 12 volts, no alt output.
The hot exterior is what I am wondering about, the rest of the engine was much cooler than the alternator,
Would the somewhat higher voltage output cause the stator windings to heat up, or is this a stator winding problem, which may or may not have fried the internal VR?
Thanks,
Doug
Yesterday volt meter, on start up was reading and fluctuating between 16-19 volts.
Ran vehicle for perhaps 1-2 minutes and decided I didn't like it.
Opened hood, the exterior of the alternator was hot, but both bearings end were cold, it wasn't bearing friction.
Started up vehicle and volts flatlined to 12 volts, no alt output.
The hot exterior is what I am wondering about, the rest of the engine was much cooler than the alternator,
Would the somewhat higher voltage output cause the stator windings to heat up, or is this a stator winding problem, which may or may not have fried the internal VR?
Thanks,
Doug
Internal short in alternator field circuit or regulator, drove alternator to full output for as long as it could stand it. Time to diagnose exactly what failed but the regulator is a good start. Alternators run hot. That is why they have fans.
my guess, but this happened to me because of a diode pack failure, it was really putting out AC voltage and boils the hell out of batteries. Then the diodes fail completely which probably the safest. New alternator fixes it, we use to solder in new diode packs in the old days to rebuild them.
Could be the diodes or the stator or both. You won't know until you take it apart and test the parts. I would replace the regulator to be safe as well. I would not try to solder new diodes into the rectifier. Just replace it. It can be done, but it is dificult to do as the heat sinks are aluminium and the diode is copper. If you try you will need button diodes.
I took a spare 10SI alt off the shelf and installed it and the voltage is rock steady now at about 13.8-14.0. The spare was originally sold as "one wire" alternator, i simply took off the rubber plug and plugged the harness into the VR tabs.
The 12SI alt will come apart today for testing. This alt was occasionally funky from the start, not long enough to diagnose, just sometimes the voltmeter would read a little "off" for short period of time.
At least an alternator change is one of the simpler things to replace, unlike a flex plate...
FWIW, with only one wire output, if all the diodes failed, it would put out 0 volts in AC mode...
Newer alternators don't use the big clunky diodes anymore that can be individually swapped out.
11-07-2021, 11:41 AM
Alternator VR failure? Internal regulator
