1932 Buick 90 Generator schematic and testing values???

[CTCV]

Not sure if the information I want is listed anywhere. I have the 1932 Buick Spec. and Adj. book but I was looking for some better info.

Some of you may know this generator it is a 940 T1.   Some say if  you touch a positive lead to the  3rd brush wire and ground the case it will spin like a motor. If it spins the generator is good. That does not tell me how good.

 

The generator is a three brush with an internal thermo switch (contact points with resistor bridge) mounted to ground. It has a cutout switch mounted to the case exterior. Two field windings in series in the case. Now to my questions.

 

I never had the resistor that bridged the thermo switch. What is/was it's OHMS value?  What is the correct/good OHMS resistance of the field windings?

A wire grounds the brushes mounting plate to the main part of the thermo switch which best I can tell allows either direct ground when cold and resistor ground when hot. If the main brushes are on a plate already grounded to the case by contact how does the thermo switch even play a part? Don't both main brushes have a direct path to ground just by contact of the mounting plate?

 

If there is a generator schematic out there I would love to see it.

 

Thanks

Tony

[Bloo]

Third brush generators work like this:

 

There are 2 circuits, the armature and the field.

 

The armature does the charging via the 2 main brushes. One main brush is grounded, the other main brush connects to the output terminal, and charges the battery through the cutout relay when the cutout relay points are closed.

 

The field is just an electromagnet in the outer frame. Controlling the field controls the generator output. There is no voltage regulation on a third brush and cutout system, only current regulation and it is a bit dodgy. The field is powered by the third brush. The setting of the third brush determines the voltage the field gets. RPM also affects this. The more voltage the field gets, the more current the generator as a whole puts out, so the third brush setting is used to set the output current of the generator.

 

The other end of the field winding in the frame is grounded normally. Since you have that thermal cutout thing, I would guess that the ground end of the field winding is grounded when the generator is cold, and if the generator starts to overheat, the points on the thermal cutout open putting the resistor in series between the ground side of the field winding and ground. Some voltage is dropped across the resistor, and that means less voltage for the field. Less voltage for the field means less output. Less output could save the generator from overheating.

 

If the resistor was missing or burned open, the generator would stop charging when the thermal cutout points opened from excessive heat.

 

Never run a third brush generator with no battery connected. There is no voltage regulation, and the voltage will soar. The field is running on part of that voltage, limited by the location of the third brush, but not limited enough. When the voltage soars, it will try to burn out the field, and probably succeed.

 

The "motoring" test you referred to is done by connecting 6 volts to the output terminal and the case, using the polarity (positive or negative ground) as used on the car. Belt or drive mechanism should be off so it can spin. The generator should run like a motor. I don't know how useful the test really is, but if the generator fails it there is definitely something wrong. It wouldn't find the open resistor, because the generator would most likely be cold.

 

There was a thread about that resistor on a Cadillac recently. I'll come back here and post a link if I can find it. I would expect the resistance to be really low. It wouldn't surprise me at all if it is less than an ohm. It is probably made of Nichrome, and probably increases resistance as it gets hot. Making or rewinding a resistor should be doable.

 

EDIT: HarryLime's got it.

Edited June 7, 2022 by Bloo (see edit history)

[HarryLime]

 

[CTCV]

Harry it appears at least your center case is very close to mine. The thermal switch with the resistor wire looks identical to mine, i just do not have the resistor wire. Can you confirm which wire goes to your third adjustable brush. Is it a field wire or the wire to the cutout

And thanks for everyone's input it my get me my output . 

 

Tony

[Bloo]

That's @Alex D.'s generator. You must follow the link to see the other thread.

 

[32buick67]

Some info on the 1931 and 1932 Buicks, hopefully this is helpful.

My 32-60 Buick has the same generator as your 32-90.

 

 

 

 

1932 Cadillac seems to be different by a bit, be cautious:

 

 

[CTCV]

32Buick67  >>>>>> OH YES IT HELPS !

 

Thanks, thanks to all.

 

Tony

[chistech]

My 32 olds has the same set up and it’s working but I’m considering putting in a Petersen regulator. I put one in my 31 chevy and it works very similar to an alternator now. It will charge more right after starting but then go almost to zero after driving the car around some. Turn on the lights and instead of dropping into the negative, it stays just above the zero. It’s a small unit which mounts to the inside of the starter band so you don’t see it. You do remove the third brush when you install it. I still run a stock cut-out with it. I’m extremely pleased with the system and we’ll see how my generator in the olds charges the more I drive it. If it overcharges too much I’m going to switch it over. I do believe the Peterson regulator only works with a negative ground system.