Generator really hot

[Hokie87]

67 bug with a rebuilt Bosch generator and original Bosch regulator. The generator gets really hot (too hot to touch and worried about solder in the armature melting hot). The bug runs fine and the generator light is not on.

Tin in the fan housing is correctly oriented (I took it out and checked).

Voltage at the battery with the car off is 12.4 V (battery also checked at my local shop and "good"). At idle and at 3000 RPM voltage at the battery is 14.6V.

Voltage at the generator (D+ to ground with DF grounded) is 20V at idle and 45+V at increasing RPM.

So, the generator seems to work and I was going to replace the regulator, BUT...when connecting 12V across D+ and DF on the generator (as to polarize) with the belt off, it did not spin. How can a generator put out good voltage but not spin with polarizing?

Any other tests to isolate whether this is a generator, regulator, neither or both problem? I'm puzzled.

[Cusser]

[herbie1200]

Generator temperature should be similar to generator pedestal temperature, they are coupled, large metallic surfaces in contact.

Voltage at idle and 3000 is high, I suspect something wrong into the regulator.

Follow this test and report us the result; this test will check a good regulator action.

1) all lights off, disconnect the warning light from the regulator and connect it to the DF terminal

2) start engine; now you should notice at idle warning light always bright on: generator is "asking" current

3) give some gas, the warning light should start to flicker between full and half brightness: the regulator starts to commutate to the resistor. The mean brightness should reduce as rpms go up

4) at high rpms the warning light (so connected!) should be always off, sign of regulator no more requiring power to the generator

Make this test and report us... don't forget to reconnect the warning light to its own terminal.

[Hokie87]

[Cusser]

[mukluk]

Having the generator spin or not while polarizing it isn't a determining factor as to whether the generator is good, the fact that it produces power within the acceptable parameters is proof that it is functioning.

The generator will heat up primarily due to the load being put on it; the more voltage and current it must generate, the more heat it will produce. I would be interested in why you're seeing 14.6v at the battery which is on the high end of what one should expect... the regulator may still be suspect, though an at rest reading of 12.4v also points toward a battery that isn't holding a full charge.
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1960 Ragtop w/Semaphores "Inga"

[Hokie87]

[sjbartnik]

You should not have to separately ground the generator body; it should be grounded by nature of being in contact with the engine case which is bolted to the transmission which has a ground strap to the body.

However if your transmission ground strap is missing or in bad shape that can cause some problems, and generator over-voltage can be one of those problems (14.6v is too high).

So I would investigate the status of your transmission ground strap and also the grounding situation of your regulator.

If your regulator mounts directly to the generator case then your regulator should be at least as well grounded as your generator. If your regulator mounts under the rear seat make sure it's well-grounded.
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1965 Volkswagen 1500 Variant S
2000 Kawasaki W650

[Cusser]

[Hokie87]

[herbie1200]

The regulator test I proposed gave good results? Strange, this is a severe test that does not pass also on car with happy owners incounscius about voltage regulations.

Anyway, if your voltage are all OK and the only issue is an (over)heating, this could be a mechanical friction...

Does the generator rotate free? No bearing or fan noises?

The last test is to use car (lights off!) with a well charged battery for 5-10minuts with generator disconnected and to notice if overheating occurs or not.

This should be a clear proof to exclude electrical problems.

[Hokie87]

Just to close this out: I installed one of those oil temperature sensors that replaces the dipstick and found that the hot generator was causing the engine to get too hot. Hot generator ==> hot fan shroud ==> hot air blowing over engine ==> green light illuminated!

I replaced the regulator with one from another car that I knew worked and still had the same hot generator problem. I then put in a new generator which solved the problem so whatever was wrong was internal to the generator. Now to tear down the generator to see if it is identifiable and rebuildable.

[calvinater]

Good job diagnosing . Let us know what you find .
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"Albatross"!