Low voltage output from generator

[ocdancer]

Hello, this is my first post.
I have a 35 ford 5-window coupe that I am getting working again. The generator isn't charging the battery. Also the ammeter doesn't show any positive amperage. But it does show about negative 15 amps when I turn on the headlights. I've searched on-line and tried to troubleshoot it. And I only have a voltmeter/ohmmeter for testing.
I disconnected both wires from the cutout, pulled the cover off and was able to trace one wire to the 3rd brush. The other wire seems to be connected to the body of the generator. And one of the field brushes is connected to the back cover of the generator.
The Ohm meter shows 0 ohms between the two wires. Is that right?
The Ohm meter also shows 0 ohms between each wire and the car's chassis. Is that right?
I used the volt meter to measure from each wire to the car's chassis. When I rev up the car the meter goes up to around one volt. And that is at pretty high revs.
I attached pics of the three brushes in the generator.
Thanks for any advice you can provide.

[1931 flamingo]

If the gen is like a Model A, the 3rd brush is adjustable to either increase or decrease outout.
Paul in CT

[ocdancer]

Thanks, can moving the 3rd brush change the output that much? I somehow thought it was a finer adjustment.
Can it be moved too close to the output brush?

[ndnchf]

That's some pretty ratty wires coming out of the generator. You may have a short. One of those wires is from the fields and grounds on cutout mounting screw. The other goes from the positive brush to the cutout "A" side. Is your cutout closing when the engine is reved up? It should close when generator voltage gets up to around 6.5v.

If it were mine, I'd pull the generator and fix that ratty wiring. Odds are the generator could use a good cleaning and inspection.

[ndnchf]

I'll add that at say 1000 rpm, the generator should be putting out enough voltage for the cutout to close. Check with your voltmeter at the "A" side of the cutout. You should see 6-7 volts. If you see higher voltage like 12-30 volts as engine speed increases, the cutout may not be closing. This causes generator voltage to rise to dangerous levels quickly and can damage the generator. If you have no voltage at the "A" cutout terminal at 1000 -1200 rpm, there is a problem with the generator. Tear it down and repair it. If the cutout is not closing, it can most likely be serviced and adjusted to work properly. See my "original cutout" post yesterday in the model A forum for more about cutout adjustment.

[ocdancer]

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Thank You 1931 Flamingo, I didn't think that brush could have that big of an affect.
I moved the adjustable 3rd brush much closer to the output brush and now I do see the amp gauge in the car show charging.

Just to share some of what I learned in case it can help some other newbie.
I did more investigation of the wiring having read a different article about the wires to the cutout being reversed. And wanted to be sure mine is correctly wired.
As I see it there is one brush on the passenger side of the generator. It has a short wire connected to the back of the housing. This is the grounding brush.
I see two brushes on the driver side of the generator, one higher and one lower.
The higher driver side brush is the adjustable 3rd brush. It is connected to one of the wires coming out of the generator.
The lower driver side brush is not adjustable. It is connected to the other wire coming out of the generator. I think this is the output brush.
Note: I had to put insulators between all three brushes and the commutator to check the wiring. Otherwise all brushes are connected through the commutator. Earlier I was trying to lift each brush with my fingers and I don't think that worked very well.

I made sure the wire from the 3rd brush connects to the insulated bolt on back of the cutout. And I made sure the wire from the output brush connects under the screw holding the cutout casing to the generator.

Thanks Again.

[ocdancer]

Thank you ndnchf.
The generator and cutout are working now.
I will look into replacing the ratty wires.

[ndnchf]

Glad you got it working!

[Terry,OH]

The wire going to the cutout is red and the second wire going to the cutout mounting screw is black. Both cloth covered wires. There is a rubber grommet where the two wires pass through the generator body. I believe Michael at Third Gen Auto has the grommet and the red wire. He may also have a piece of cloth covered black wire.

[rotorwrench]

Three brush generators are a good where a charging current is not more than 20-amps max. The main brushes consist of the power brush and the ground brush. The power brush wire is the red one that exits the generator. The ground brush is just that. It's where the armature gets its ground inside the generator. The 3rd brush is connected to the field coil on one end and then the field coil is connected to common ground on the other end (through two coils for the field otherwise known as a shunt coil). I'm not sure why they decided to use a ground wire to exit the case & connect to the cut out other than to insure a common ground to all components of the system. The model A didn't have an external ground wire on any of the three different types they used.

The battery provides all the voltage sense that the generator needs to maintain the system voltage so there is no need for a regulator. The current limiter is the 3rd brush that can be adjusted by the operator depending on how the car is operated. If the car is seldom operated at night then the 3rd brush can be set for enough amperage to operate the cars system without headlights but enough more to charge the battery. If a person drives at night a lot then the charge current can be adjusted to keep the battery charged with the headlights on. If the car is driven for long lengths of time during daytime hours then the battery will be overcharged when the headlights are off. A person either has to readjust the charging current or leave the headlights on all the time. This inconvenience is one reason that the three brush generators were dropped for the two brush voltage and current controlled systems in 1939/40 time frame. No muss and no fuss with a two brush and they could be bumped up for higher current output too. Much better for those winter nights with the heater on high and the radio on for weather reports.

[Tim Ayers]

I agree about the wires. Until they are replaced, I'd tape them up to make sure they are grounded or shorting out.

Here is a trick to clean up the contact area of the armature. Get a fresh pencil with a soft eraser. As the generator is running, stick the eraser end into the slot and run it over the brush contact surface of the armature. It cleans it us nicely and may help you to get some better voltage from your generator.

[B-O-B]

Looks to my old & tired eyes that you could use some new brushes when you replace the frayed wiring. Don't forget to polarize the gen after taking it apart if you do. Just a reminder. I need them all the time. I even resort to writing my self notes, but half the time forget read them. ho ho
Welcome to the Barn & belated Happy Birthday.

[ndnchf]

I may be wrong, but I believe the reason they had the field wire coming out through the grommet and grounding to the outside rather than grounding on the inside, was for the possible upgrade to an early 2-charge (high/low charge rate) regulator. The cutout could easily be replaced with a 2-charge regulator by simply moving the field wire from its ground screw to the regulator field terminal.

[rotorwrench]

The 2-stage cut out was likely the reason for that external shunt field ground wire. Beginning in 1934, it was an option for cars equipped with a radio set. They were an oblong shaped unit with a current sense relay next to the cut out inside. The relay would put a load resistor in the field line for normal output but would kick in a full field circuit when the current draw increased to a certain point. This would require an initial 3rd brush setting with no need to reset during operation or at least that was the plan.

Ford had complaints on these so they were eventually dropped around 1936. The external wires were retained until the 2-brush generators came out as far as I know.

[ndnchf]

Great info rotorwrench, thanks for sharing.