The Ford Barn

johnbuckley · 09-04-2020, 04:55 AM

I suspect that the voltage required to close the cut-out contacts is surprisingly high possibly 9.5 v, of course when they close the volts drops immediately to realistic levels of about 7.5v-8v). But has anyone actually measured the voltage required to close the cut-out points?

Kurt in NJ · 09-04-2020, 09:08 AM

The specifications call for 7-7.5 volts to close cutout, open at 2-2.5 amp discharge

Patrick L. · 09-04-2020, 10:56 AM

I agree the cut in should be in the low 7 volt range.

My question is what cut out you're using, repo or original. Thats probably a dumb question as I think its probably an original, but had to ask.

katy · 09-04-2020, 11:14 AM

Using a diode for a cutout would put the "set" voltage at about 1/2 volt over the battery voltage.

rotorwrench · 09-04-2020, 11:50 AM

With a diode, it just starts generating straight away but doesn't flow much current until the voltage is up to par. Folks have to remember the current part of the equation as well a the voltage. Voltage is just the carrier. The only set voltage in a 3-brush system is the battery.

With a cut out, they just wanted to make sure it would match the battery voltage when bringing the system on line. It's just a relay that takes a certain amount of magnetic gauss to pull the relay to the closed switch position and has a shunt winding to measure voltage output. The tension on the switch arm sets the amount that it takes to close the switch. Once the switch is closed, the battery still regulates the voltage. When current and voltage oppose each other too much at engine shut down or extremely low rpm, the cut out will open.

The voltage specifications for closing and for opening are just for test purposes. In real function, the generator amp and voltage output is what brings the generator on line. At low rpm the battery amperage starts to override the generator output amperage so the magnetic gauss in the cut out pole core dissipates pretty fast.

johnbuckley · 09-04-2020, 12:17 PM

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Quote:

Originally Posted by Kurt in NJ

The specifications call for 7-7.5 volts to close cutout, open at 2-2.5 amp discharge

Where's that spec come from, Kurt?

Kurt in NJ · 09-04-2020, 03:03 PM

dyke's encyclopedia, nineteenth edition, page 1136
there is a whole listing of electrical specs, I see at the bottom there is a footnote---from "the standard auto electricians manual"

johnbuckley · 09-05-2020, 02:01 AM

Great! Thanks Kurt.

09-04-2020, 04:55 AM	#1
johnbuckley Senior Member Join Date: Jul 2010 Location: United Kingdom Posts: 1,441	Cut-Out closure trigger voltage I suspect that the voltage required to close the cut-out contacts is surprisingly high possibly 9.5 v, of course when they close the volts drops immediately to realistic levels of about 7.5v-8v). But has anyone actually measured the voltage required to close the cut-out points?

09-04-2020, 09:08 AM	#2
Kurt in NJ Senior Member Join Date: May 2010 Location: on the Littlefield Posts: 6,158	Re: Cut-Out closure trigger voltage The specifications call for 7-7.5 volts to close cutout, open at 2-2.5 amp discharge

09-04-2020, 10:56 AM	#3
Patrick L. Senior Member Join Date: May 2010 Location: Largo Florida Posts: 7,225	Re: Cut-Out closure trigger voltage I agree the cut in should be in the low 7 volt range. My question is what cut out you're using, repo or original. Thats probably a dumb question as I think its probably an original, but had to ask.

09-04-2020, 11:14 AM	#4
katy Senior Member Join Date: Jun 2015 Location: Red Deer, Alberta Posts: 5,043	Re: Cut-Out closure trigger voltage Using a diode for a cutout would put the "set" voltage at about 1/2 volt over the battery voltage. __________________ If you don't hear a rumor by 10 AM, start one!. Got my education out behind the barn! Last edited by katy; 09-05-2020 at 09:56 AM.

09-04-2020, 11:50 AM	#5
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,426	Re: Cut-Out closure trigger voltage With a diode, it just starts generating straight away but doesn't flow much current until the voltage is up to par. Folks have to remember the current part of the equation as well a the voltage. Voltage is just the carrier. The only set voltage in a 3-brush system is the battery. With a cut out, they just wanted to make sure it would match the battery voltage when bringing the system on line. It's just a relay that takes a certain amount of magnetic gauss to pull the relay to the closed switch position and has a shunt winding to measure voltage output. The tension on the switch arm sets the amount that it takes to close the switch. Once the switch is closed, the battery still regulates the voltage. When current and voltage oppose each other too much at engine shut down or extremely low rpm, the cut out will open. The voltage specifications for closing and for opening are just for test purposes. In real function, the generator amp and voltage output is what brings the generator on line. At low rpm the battery amperage starts to override the generator output amperage so the magnetic gauss in the cut out pole core dissipates pretty fast. Last edited by rotorwrench; 09-04-2020 at 12:14 PM.

09-04-2020, 03:03 PM	#7
Kurt in NJ Senior Member Join Date: May 2010 Location: on the Littlefield Posts: 6,158	Re: Cut-Out closure trigger voltage dyke's encyclopedia, nineteenth edition, page 1136 there is a whole listing of electrical specs, I see at the bottom there is a footnote---from "the standard auto electricians manual"

09-05-2020, 02:01 AM	#8
johnbuckley Senior Member Join Date: Jul 2010 Location: United Kingdom Posts: 1,441	Re: Cut-Out closure trigger voltage Great! Thanks Kurt.