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Old 07-13-2020, 06:31 PM   #1
Phil Gillespie
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Default How to test a Generator Cut Out

My 38 PU is fitted with a 2 brush generator through the cut out then through an adjustable rheostat adjusted dependant upon load ie lights in use.
Know its not correct and should fit a voltage regulator for correct operation.
However how do you verify correct operation of cut out.Its the round Ford type which cannot be opened up.
Appreciate any advice on this one.
Phil NZ
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Old 07-14-2020, 12:36 AM   #2
flatheadmurre
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Default Re: How to test a Generator Cut Out

A cutout is for use on a 3-brush so i assume a typo ??
If you try and use a cutout on a 2-brush you will overload the points and fry it probably to start with...then activating the field with a reostat you will have no correct voltage or any current regulation so besides damaging the cutout your battery is at risk to if run for a longer period of time...since you will either over or under charge it.
You want bench test a cutout in a safe way use benchpower supply and a battery...when you raise the voltage to it should cut in...lowering it should drop out...condition of points needs a load and measuring voltage drop over it.
Why not install a proper regulator ?
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Old 07-14-2020, 12:40 AM   #3
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Default Re: How to test a Generator Cut Out

Phill you could run a wire from one side terminal stud to the other ,if the unit is faulty and the genny is ok it should show a charge on the Amp each time you touch the end ,
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Old 07-14-2020, 02:05 AM   #4
Phil Gillespie
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Default Re: How to test a Generator Cut Out

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Originally Posted by FlatheadTed View Post
Phill you could run a wire from one side terminal stud to the other ,if the unit is faulty and the genny is ok it should show a charge on the Amp each time you touch the end ,
Thanks Ted thats what I was thinking. Appreciate your advice.
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Old 07-14-2020, 02:08 AM   #5
Phil Gillespie
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Default Re: How to test a Generator Cut Out

Quote:
Originally Posted by flatheadmurre View Post
A cutout is for use on a 3-brush so i assume a typo ??
If you try and use a cutout on a 2-brush you will overload the points and fry it probably to start with...then activating the field with a reostat you will have no correct voltage or any current regulation so besides damaging the cutout your battery is at risk to if run for a longer period of time...since you will either over or under charge it.
You want bench test a cutout in a safe way use benchpower supply and a battery...when you raise the voltage to it should cut in...lowering it should drop out...condition of points needs a load and measuring voltage drop over it.
Why not install a proper regulator ?
No typo this was how it was set up its a two brush.. But will be best and less hastle to go with a proper voltage regulator.
Phil NZ
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Old 07-14-2020, 08:14 AM   #6
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Default Re: How to test a Generator Cut Out

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Quote:
Originally Posted by Phil Gillespie View Post
No typo this was how it was set up its a two brush.. But will be best and less hastle to go with a proper voltage regulator.
Phil NZ
A "proper" voltage regulator? In 1938? I didn't realize Ford was fitting voltage regulators to 1938 models.
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Old 07-14-2020, 04:18 PM   #7
Phil Gillespie
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Default Re: How to test a Generator Cut Out

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A "proper" voltage regulator? In 1938? I didn't realize Ford was fitting voltage regulators to 1938 models.
No there was no 'proper voltage regulator in 1938" but this PU is also fitted with an 8BA and hydraulic brakes so its another item to make it more user friendly for driving purposes. The fitted generator is a 2 brush, not correct, though a cutout then via a variable adjustable resistor on dash which is adjusted to give required amps on gauge dependant on load ie lights in use etc.
not ideal by any means but now time to correct.
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Old 07-14-2020, 05:56 PM   #8
rotorwrench
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Default Re: How to test a Generator Cut Out

On Fords, the two brush should have a field terminal, an armature terminal, and a ground terminal. The 3-brush units will only have one terminal or just a wire exiting the body to connect to the cut out. A 2-brush unit should be using a 3-pole voltage regulator if it's an 8BA unit. With no voltage regulator, current limiter, and cut out poles the two brush will not be functioning as it should.

A generator can generally be converted to work as a 2-brush if it was a 3-brush by elimination of the 3rd brush and installation of the 2-brush type field coils. Some of the early two brush units have a 2-pole voltage regulator that has a dual purpose voltage regulator and current limiter in the same pole with a cut out next to it. These old dudes are getting harder to find these days. They usually have an armature wire and a field wire that protrude from the generator body so as to connect to the early style regulators.

The 3-brush is limited on output to around 20-amps and it puts out what ever amperage that the 3rd brush is set to. The battery regulated the voltage so they have to be well connected to a battery or they can get too hot. They lose efficiency when the rpm is increased so they aren't an ideal set up for a traveler that drives at night a lot.

Some folks have modified the 3-brush types with modern electronic current regulators. Some of these still use the 3rd brush and some don't. They still use the battery for voltage control but the current is switched on and off rapidly for control. They will reduce current output a lot when the battery is fully charged and pick up the load when the lights are turned on but they are still limited in their output capability.

Last edited by rotorwrench; 07-14-2020 at 06:36 PM.
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