The Ford Barn

Tom Walker · 08-26-2013, 09:29 AM

Reading Barnfind08's post on generator wiring, I wanted to bring up something that has been brewing in my mind for a while. My question is....is there any way of varying the charge output of an old Ford equipped with a 3 brush generator with 2 wires coming out of it, other than by adjusting the movable brush?

I have sent my "one wire" generator off to be fixed, it stopped charging. While it was still on the car, I read up on 3 brush generators so I could test it. The "one wire" unit has its output to the cut-out then to the ammeter to provide charging. The "2 wire" unit has the same output wire, with another simply going to ground under the cut-out case.

This second wire is, I believe, the ground for the field coils. On the "one wire" unit, the field coils are grounded inside the casing. In other words, the 2 gennies are exactly the same (in their wiring, at any rate), but one has its field coils grounded outside the case, the other inside.

So if you have a one wire genny, you cant do much about the output other than buy a clever cut-out/regulator box, and manually adjust the movable brush. If you have a 2-wire genny, I believe you can vary the charge by running the field coil ground wire through resistance.

It seems to me that this could provide you with a useful control of genny output, at the cost of a bit of wire, a resistor, and a switch. A two way switch on the dash could send this field coil wire straight to ground (when lights are on) or to ground via resistance (lights off). Play with the movable brush to get the basic output right. I had an old tractor that had a 2 stage charging system, and I think the resistance was provided by a bulb,which lit to remind you that you were on low charge. Now I think I understand a little more about how it worked.

I suppose I go back to my original question...was there ever any switched output variability on the 3 brush, 2 wire generator equipped Fords?

Thanks, Tom.

koates · 08-26-2013, 10:40 PM

Hi Tom, you could set up a system using a resistor and a two way switch exactly as you described. You would have to work out the ohms value of a wire wound resistor by trial and error but around one ohm might be a starting point. Many early english cars and motor cycles had such a system fitted as standard equipment in the 1920s & 1930s. Another option is to buy a replica of the round ford cutout which has a regulator built inside of it. They fit right on top of the generator with no alterations to gen or wiring. Made by "FUN PROJECTS, St. Charles, IL. " Several variations available and cost around $90.00 each. Look them up on the net. Regards, Kevin.

Kurt in NJ · 08-26-2013, 11:19 PM

Yes, you need the "oval" cutout, it has a rudimentary voltage regulator in it, it added a resistor to the field ground to cut the output --or there are also true voltage regulators that fit in the cover band, ----or the above mentioned "fun projects" cutout type that must just dump excess to ground.

On my model A (about the same as a V8 3 brush gen) I set the charge rate to 15 amps, just enough to have a +1 amp with halogen bulbs, when I think the battery has had enough charge during daylight driving I turn on the lights ---for me this works, I have long battery life, never charge other than driving (got 16 years from Optima)

One has to remember that these cars were not designed to always have a + charge , just to have more of charging than discharging, I have my rate high to make up for months of sitting,and 50% night driving, if I drove the car more I would reduce the rate ---I reduced it to about 6 amps for a 2000 mile trip

bobH · 08-26-2013, 11:52 PM

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Might try a search on this one... here, and on the Model A forum, and on Ahooga. This has been posted before, and I believe there are at least three answers, besides the 'fun-projects' device. One, is a regulator made & sold by Tom Weisenberg (sp?), over on the A forums. Another, is another regulator made & sold by another fellow, who I have currently forgotten - the A guys will help. And, the third, is to use an ordinary 6V regulator, like would be used with a two-brush generator of later years. Tom Weisenberg was the one who posted on how to do this. Part of his description, I think, is to unground the field wire (under cutout screw), and connect it to the field on the mechanical regulator. If you go back & research this, you might come to believe that the 'fun-projects' device may not be your choice. JMO

08-26-2013, 09:29 AM	#1
Tom Walker Senior Member Join Date: Aug 2012 Location: Leicester. UK Posts: 404	Early generator charging output Reading Barnfind08's post on generator wiring, I wanted to bring up something that has been brewing in my mind for a while. My question is....is there any way of varying the charge output of an old Ford equipped with a 3 brush generator with 2 wires coming out of it, other than by adjusting the movable brush? I have sent my "one wire" generator off to be fixed, it stopped charging. While it was still on the car, I read up on 3 brush generators so I could test it. The "one wire" unit has its output to the cut-out then to the ammeter to provide charging. The "2 wire" unit has the same output wire, with another simply going to ground under the cut-out case. This second wire is, I believe, the ground for the field coils. On the "one wire" unit, the field coils are grounded inside the casing. In other words, the 2 gennies are exactly the same (in their wiring, at any rate), but one has its field coils grounded outside the case, the other inside. So if you have a one wire genny, you cant do much about the output other than buy a clever cut-out/regulator box, and manually adjust the movable brush. If you have a 2-wire genny, I believe you can vary the charge by running the field coil ground wire through resistance. It seems to me that this could provide you with a useful control of genny output, at the cost of a bit of wire, a resistor, and a switch. A two way switch on the dash could send this field coil wire straight to ground (when lights are on) or to ground via resistance (lights off). Play with the movable brush to get the basic output right. I had an old tractor that had a 2 stage charging system, and I think the resistance was provided by a bulb,which lit to remind you that you were on low charge. Now I think I understand a little more about how it worked. I suppose I go back to my original question...was there ever any switched output variability on the 3 brush, 2 wire generator equipped Fords? Thanks, Tom. Last edited by Tom Walker; 08-26-2013 at 09:35 AM. Reason: word left out

08-26-2013, 10:40 PM	#2
koates Senior Member Join Date: May 2010 Location: Melbourne Australia. Posts: 2,079	Re: Early generator charging output Hi Tom, you could set up a system using a resistor and a two way switch exactly as you described. You would have to work out the ohms value of a wire wound resistor by trial and error but around one ohm might be a starting point. Many early english cars and motor cycles had such a system fitted as standard equipment in the 1920s & 1930s. Another option is to buy a replica of the round ford cutout which has a regulator built inside of it. They fit right on top of the generator with no alterations to gen or wiring. Made by "FUN PROJECTS, St. Charles, IL. " Several variations available and cost around $90.00 each. Look them up on the net. Regards, Kevin.

08-26-2013, 11:19 PM	#3
Kurt in NJ Senior Member Join Date: May 2010 Location: on the Littlefield Posts: 6,159	Re: Early generator charging output Yes, you need the "oval" cutout, it has a rudimentary voltage regulator in it, it added a resistor to the field ground to cut the output --or there are also true voltage regulators that fit in the cover band, ----or the above mentioned "fun projects" cutout type that must just dump excess to ground. On my model A (about the same as a V8 3 brush gen) I set the charge rate to 15 amps, just enough to have a +1 amp with halogen bulbs, when I think the battery has had enough charge during daylight driving I turn on the lights ---for me this works, I have long battery life, never charge other than driving (got 16 years from Optima) One has to remember that these cars were not designed to always have a + charge , just to have more of charging than discharging, I have my rate high to make up for months of sitting,and 50% night driving, if I drove the car more I would reduce the rate ---I reduced it to about 6 amps for a 2000 mile trip

08-26-2013, 11:52 PM	#4
bobH Senior Member Join Date: May 2010 Location: so cal, placerville, vegas Posts: 1,394	Re: Early generator charging output Sponsored Links (Register now to hide all advertisements) Might try a search on this one... here, and on the Model A forum, and on Ahooga. This has been posted before, and I believe there are at least three answers, besides the 'fun-projects' device. One, is a regulator made & sold by Tom Weisenberg (sp?), over on the A forums. Another, is another regulator made & sold by another fellow, who I have currently forgotten - the A guys will help. And, the third, is to use an ordinary 6V regulator, like would be used with a two-brush generator of later years. Tom Weisenberg was the one who posted on how to do this. Part of his description, I think, is to unground the field wire (under cutout screw), and connect it to the field on the mechanical regulator. If you go back & research this, you might come to believe that the 'fun-projects' device may not be your choice. JMO