ammeter pegs even when battery is fully charged

[aviator37]

Any thoughts on this? Ammeter pegs all the way even when battery is fully charged. All original set up, 6 volts, original type generator.

[Patrick L.]

There is no regulation in the Model A charging system. When you say the ammeter pegs, in which direction does it peg ? to the positive or negative ? Does the engine have to be running to make it peg ?

These are questions I think need to be answered first, but, thinking that you mean it pegs full positive then you could start by adjusting the third/movable brush to try and achieve a charge rate of 3-5 amps at a fast idle.

[aviator37]

Yes it pegs positive. I don't get warm fuzzys about the accuracy of this meter. I may try to measure it with my Fluke before adjusting. Do you have experience with a current measurement like that?

[Mitch//pa]

Originally Posted by aviator37

Yes it pegs positive. I don't get warm fuzzys about the accuracy of this meter. I may try to measure it with my Fluke before adjusting. Do you have experience with a current measurement like that?

Correct... just watch out for false digital readings from ignition interference.

Usually the flukes have a smooth button to help with that..

[Tom Wesenberg]

I never use my digital meter when working on cars. I like the analog meters.

Here's two pictures to show the brush end plates with brushes. Until March 1930, the rear end plate used a ball bearing, then Ford switched to a bushing. Notice in the first picture, the brush on the left is the ground brush, and the brush on the right is the output brush. The thin brush between them is the field power supply brush, called the "third brush". As you move that brush away from the ground brush and toward the output brush on the right, it will be sending more power to the field coils. More power means greater output.

Since your generator is putting out too much amperage now, you want to move the brush towards the ground brush. It may be stuck from years of never being moved, but when you remove the generator band, you can use a screwdriver against the open slot and push the third brush upward to lower the output. Then start the car and see if you have lowered the amps to a safe level.

The third picture shows a cutaway generator that was on display at the Model A Museum at the Gilmore Car Museum in Hickory Corners, Michigan.

[Patrick L.]

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I don't think I'd worry to much about how accurate the ammeter is. Just turn on the lights or step on the brake and see what discharge you have. Depending on the light bulbs you're using the reading will vary, but, still will probably be around 8-10 amps.

Try prying up the third brush as Tom mentioned to see if you can reduce the output to about 5 amps or a bit less.

[Mike V. Florida]

That's one hell of a generator that will still put out 20 amps into a system that has no problems.

Does it move off peg with the car off?
Does it move off peg with the lights on and horn blowing?

[Tom F OHIO]

If it stays in that position all the time no matter what you turn on then maybe there is a chance that the amp meter is stuck in that spot. Maybe try another amp meter and see what happens.

[aviator37]

ammeter moves to center when shut off. Meter seems to be OK. I will try to make an accurate measurement with an external meter.

[Patrick L.]

It still seems as though you have a simple generator or cutout issue. I'm leaning more towards the generator, but, try and determine if the cutout is an original or aftermarket. The aftermarkets tend to be junk.

[Jim M]

What cut out? I thought the generator just puts out at a constant rate and the ammeter just goes down when there is a significant draw - like lights.

[Tom Wesenberg]

The cutout is simply an OFF-0N switch. On when the generator puts out more than 6 volts, and off when the generator output falls below 6 volts.

One more thing to check is the two wires connected to the adjustable and output brushes. I've seen generator shops mix them up and burn up two generators. The field wire must connect to the adjustable brush, and the output post must be connected to the stationary brush, which is half way around from the ground brush.

[msmaron]

Originally Posted by Jim M

What cut out? I thought the generator just puts out at a constant rate and the ammeter just goes down when there is a significant draw - like lights.

are you saying your using a generator a NO CUTOUT????