Alternator is apparently producing so much load that belt slips/squeals, and actually burns belt off (it did initially). Alternator and battery are OK, confirmed with multiple batteries and working alternators.

Advice will be appreciated.

Not too long before this I repainted all front accessory brackets. Bad ground?

 

So tighten the belt, and make sure pullies are aligned. Misalignment will destroy a belt pretty quick.
When you say alternator is "OK", what exactly does that mean? It may be charging but have bad bearings...

 

Bad ground won't cause that.

First thing to do is figure out why it's slipping. Is coolant getting on it, is it loose, does the alt move when the engine is revved (missing a bracket or something like that), does some particular accessory such as the cooling fan have a correlation, and so forth.

The alt "should" put some degree of load onto the belt. After all, the electrical power that comes out of it, isn't just miracled up inside there somehow; the alt takes in MECHANICAL power from the belt, and converts it to an equal amount of ELECTRICAL power which it puts on that big stud on the back. Minus its own losses of course. I'd expect a typical car alt to be maybe 60% efficient or so; therefore at a typical car electrical load of let's say 25 to 40 amps for the ignition, blower motor on a low speed, a light or 2, the stereo, gauges, ... that's something on the order of 4 or 500 watts (½ kW) out. 1 HP = 746 W; so at 60% efficiency, that means the alt is drawing roughly 1 HP of mechanical power. Maybe another 1 - 1.5 HP when the radiator fan is running; it's rather hungry.

If multiple alternators and batteries have done the same thing, the problem is most likely NOT in the alt or batt; but rather in something else.

 

Not sure if correct, but the voltage on the rear stud matches the battery voltage. Red prong on stud and black on battery terminal. Then red prong and black prong on the two battery terminals. Maybe doing that wrong. But idea is see if output of alternator is not some huge number compared to battery. Meaning alternator thinks it needs to perform max load out and turn harder.

Belt is aligned. Original bearings, rebuild bearings, and spare alternator bearings are smooth.

Spare alternator behaves same as original before rebuild and original after rebuild.

Seems like a simple system. But have no idea of cause or better/proper way to test output/ie load.

Why would an alternator turn hard? Load? Bearings of course? Acts like it windings are creating a field working against itself.

 

It is indeed a simple system. It's just a car. Doesn't get much simpler.

The voltage between the alt stud and the case should be marginally higher than the voltage across the batt terminals. I'd expect something on the order of a tenth of a volt or 2 tenths maybe. Should be 14.1 - 14.4 across the alt.

 

I think I’ll systematically pull fuses to test. And unplug fan. Start with fan. Nothing to lose. And lastly I can drive it to a shop with the belt off.

 

What does the alternator pulley look like? It should look like this \_/ and not a "U". If it's worn so much that the belt bottoms in the pulley's v-groove, then that's the problem. The drive needs to happen on the sides of the V.

 

Pulley is a V. High quality belt.

Hoping and anticipating to find something simple as this progresses. It is something I’ve never experienced or heard of. My experiences have included not charging and bad bearings. Nothing like this.

 

This might sound stupid, but post a few pictures. Maybe one of us will see something you are overlooking.

You said you painted the brackets recently. Could you have mixed up a couple of bolts where one now sticks out too far and is dragging on the alternator pulley?

 

Pics tomorrow. Thanks.

 

pull the belt off,, turn the alternator ,, spin it it should be free to spin,, check the pulleys line up with a straight edge,, put a new belt on and dont spray crap on it,,
make sure the pulleys are clean and not greasy ,,, rusty or pitted,,, dont use chinese chrome crap pulleys the chrome comes off and makes issues,,, aluminium pulleys are for no reason,, use the GM pulleys of steel they work end of story.

Dont over tighten the belts or you will flog the bearing out of the alternator and stuff the belts.

its a simple job.

 

 

eliminate guess work and hours on compues talking to people.

go to a licenced auto electrician,, make sure he or she is over 40 years old. ,,, parts in america are cheap.
its a simple job.

i bet you need an alternator

 

 

Fixed!! Embarrassed to say belt not tight enough. Best I can tell for now. Used prybar which I’ve never had to do before on this car. But I tested and inspected and then tested and inspected. Then again. All sorts of troubleshooting. Learned a lot besides how tight to make that belt on this car, which is good for the future. I’m just happy it seems to be working again.