Generator question

[katy]

When "motoring" a Model a generator, how fast should it turn and in what direction?
I replaced the field coils in the generator and now it doesn't charge.

[nkaminar]

Try zapping the field coils. There is a small amount of residual magnetizem that is needed to get the generator generating. Put some cardboard under the third brush and run a wire from the post on the starter switch to the brush for just a fraction of a second.

Also use your multimeter in the ohm setting to make sure all the wires are connected correctly and not grounded where they shouldn't be. I was assuming you did that already. And check the cutout by measuring the generator output at the stud coming out of the generator.

The generator will turn very slowly in the direction that it turns when connected to the engine with the fan belt. The generator would turn a lot faster if the timing of the brushes and wiring were set up to be a motor instead of a generator.

[katy]

The generator will turn very slowly in the direction that it turns when connected to the engine with the fan belt.

Thanks, that's what it does and I wondered if that was correct.

[rotorwrench]

Since they are not a motor, they will have low torque and rpm compared to a normal electric motor design of the same size.

I don't motor them to polarize the fields. The fields are connected to the 3rd brush and ground so I isolate the 3rd brush by disconnecting the lead and jumper it to the negative post on the battery. I then jumper the positive post of the battery to the case ground of the generator momentarily. This puts a good magnetic gauss into the field pole shoes with proper polarity for positive ground. If polarizing through the armature, It doesn't get as good a magnetic gauss level as with direct field coil magnetization.

A fellow I used to work for would attach a test light to the output terminal and the other to the case and spin it up with a wire brush wheel on a grinder motor. A better way would be to attach an ammeter in the power line and see what kind of amperage will come out of it but the test light will tell if it will generate or not. Put the cut out on and install if it generates current and then use the amp meter in the output line to adjust the 3rd brush in the car.

[nkaminar]

Rotorwrench, You and I are of the same mind. I suggested the same thing in Post #2 but using a different technique.

The generator would be a good motor with some slightly different wiring and different timing on the brushes.

If the generator is motoring that indicates that it is good. I would look at the cutout or a fuse if that is in the circuit.

[ndnchf]

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Watch my video on polarizing a Ford 3 brush generator.
https://youtu.be/cvTico_p6K0?si=IGWUgXXWk-pjnvGH

[johnbuckley]

Originally Posted by nkaminar

If the generator is motoring that indicates that it is good.

Not always! ( don't ask!)

[katy]

Originally Posted by johnbuckley

Not always! ( don't ask!)

That's scary, what did you do to it?

[johnbuckley]

got another one that did work!

[katy]

The generator motors, so I'm assuming it's good, but it doesn't put out. It has the diode type cutout which tests good. W/the engine running, putting a jumper across the cutout causes the ammeter to show a discharge.
I'm assuming that there's still something wrong w/the generator, but what?
The new field coils have one red and one brown lead, I've read that the red lead should go to the third brush and the brown lead to ground, that's what I have now. I tried reversing the leads and no joy.
It reminds me of Marshall's saga w/a generator.

Tom Wesenberg posted this: https://www.fordbarn.com/forum/showthread.php?t=71055

Gonna try it

[nkaminar]

You assumption is correct. Do the test that Tom suggested but check all the connections. Make sure the bushes are making good contact to the commutator and wired up the right way. Unlikely, but check that the generator has a good ground to the engine and the engine to the ground connection at the battery.

[ndnchf]

I restore a lot of generators and occasionally see one that motors, but won't charge. It is usually caused by the output being grounded around the terminal post, a partially grounded field, or a weak brush spring or poor brush contact with the commutator. New brushes need to be sanded in to fit properly. Last year a guy sent me his generator after several days of troubleshooting the same issue. It turned out the be the field interconnection point was grounding on the through bolt. An easy fix.

Steve Blancard

[katy]

I'm stumped.
I still can't get this generator to put out. I've installed the new field coils 4 different ways, on each way I connected the leads 2 different ways, which gave a total of 8 different ways.
I used Tom W's method to check magnetic polarity of the fields. Also did motoring rotation check.
I patched up the original field coils, reinstalled them, did the magnetic polarity check, voltage polarity test, motoring check, checked for grounds and shorts.
Borrowed a growler to test the armature for shorts.
Test motored the unit after that, still no joy.
I must be missing or overlooking something, but I can't think of what.

[ndnchf]

There is only one correct way to wire the fields. Over the period of model A production. They grounded fields 3 different ways. How are yours grounded? What is the resistance through both fields? It should be .9 - 1.0 ohms. Did you check the armature for opens, shorts and grounds? Any one of these 3 can cause problems. Did you sand in the brushes for full contact? Lastly, are you certain the cutout is working properly?

[Marshall V. Daut]

Push the third brush to maximum output, meaning as you are looking at the side of the generator that faces out, push the third brush all the way DOWN to increase the charging rate for a test. If the third brush is set too far up, the generator may motor, but it won't put out any charge. You can hear and see the difference in the speed that the armature turns over when the third brush is set at either extreme. I had a frustrating experience after going through a generator that just wouldn't charge. 'Turns out the third brush was set way up top and wasn't putting out anything, besides turning over slowly. I finally realized my mistake, moved the third brush down (in the direction of engine rotation) and viola! The generator started charging! I set the third brush halfway between the extremes and was very happy with the result.
Marshall

[katy]

Thanks for the replies,

Originally Posted by ndnchf

There is only one correct way to wire the fields. Over the period of model A production. They grounded fields 3 different ways. How are yours grounded? What is the resistance through both fields? It should be .9 - 1.0 ohms. Did you check the armature for opens, shorts and grounds? Any one of these 3 can cause problems. Did you sand in the brushes for full contact? Lastly, are you certain the cutout is working properly?

Field coils are grounded with one wire coming outside the case to ground.
Field resistance is ~ 1 ohm
Armature was checked for opens: none, shorts: none, ground:, none.
Brushes are making full contact.
Diode cutout tests good, No output from generator at cutout input.

Marshall, third brush was set half way, at that setting generator output shows 0 volts, I'll try full down and see what happens.

[ndnchf]

Well. A growler will tell you if an armature is definately bad, but can only tell you that it MIGHT be good. The tests are not foolproof. Ive restored a couple generators that were like this. Do you have another, known good armature you can swap in?

As a last resort, you are welcome to send it to me and I'll get it sorted out. Or I have restored generators available.

Steve

[katy]

Did a test run w/3rd brush all the way down and generator puts out 6 volts, increase RPM no change.

FWIW, generator worked before I replaced the crappy looking field coils.

Thanks for the offer to sort it out, the problem is that you are in the US and I'm in Canada.

[ndnchf]

Yeah, shipping would be an issue. But you could send it go Mike Hill in Calgary AB.

[30Tudor]

I would be happy to look at it and test it. Please PM me with your contact info.

Mike Hill