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Old 09-15-2019, 06:21 PM   #10
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Join Date: Jun 2010
Location: San Antonio, Texas
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Default Re: 3 brush generator ????

A person has to be aware of the electrical theory behind the early auto generators used by Ford. They used the most simple design that was available. The field design is such that it will produce a voltage consistent with the needs of the battery.

The cut out it there to keep the generator from motoring after the engine is shut down. It is brought on line by the power developed from the residual magnetism in the field pole shoes when the engine comes to life and starts turning it. This is where polarization of the field shoes is important.

The third brush is the current limiter in the system and it the only adjustment that can be made for the charging process. A good quality amp meter is required when adjusting the third brush per the basic adjustment procedures that Ford used. I don't think I would trust the dash gauge to make the adjustments. Originals are trustworthy if they still function normally but I would still use a separate meter.

The 3-brush units are limited on how much amperage they will put out and are taxed when driving the car a lot at night with the lights on. This is why they finally went to a more modern 2-brush design in 1939 but they had to have a voltage controller box that had the cut out, a voltage regulator pole, and a current limiter pole in order to function and be able to put out 30 to 35 amps. Not all 39 models were so equipped since it was a change over year. Deluxe models would be more likely to have the 2-brush generator with the 3 pole voltage regulator.

There are more than a few different cut out looking devices available and some have voltage regulators (Fun Projects is one). The oval shaped units are hard to find in good condition since they were relatively short lived.

If it won't generate an amperage then something is wrong with it. It could need cleaning, lubrication, & new brushes but then it could have a damaged field or armature too.

Last edited by rotorwrench; 09-15-2019 at 06:31 PM.
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