Farmall M Voltage Regulator

Anonymous-0 · May 2, 2009

I recently acquired a 1951 Farmall M with 12 volt electrical system (negative ground) on which the generator has never worked. I finally found some time to troubleshoot the problem and traced out all wiring which looks to be correct. However, I have no voltage to the field terminal of the generator. Examining the voltage regulator internally, I find the "F" terminal which feeds the field terminal on the generator actually connects to ground - either through a contact or through a resistor internal to the regulator. No way this can supply the necessary field voltage to the generator! So I'm wondering if someone has either put the wrong type generator or the wrong type voltage regulator on this tractor? Any suggestions on how to best correct this would be much appreciated. Also, does anyone know if this tractor originally had a 6 volt system?

John T · May 2, 2009

You have A CLASS A CHARGING SYSTEM so the purpose of the VR is to supply A GROUND FOR THE GENNYS FLD POST either a dead ground for high max charge or a resistive or switched (relay chatter) ground via a field current control relay.

Some Fords used a Class B system where the VR supplied voltage to the Field BUTTTTT you have an A system. The gennys FLD post needs a ground NOT a voltage source on that A system. Likewise a B generator (some Ford products) has an internally grounded Field. Your A type genny has its Fields input connected to the ARM terminal and it terminates out the FLD post where it gets a ground either via a VR or a LHBD light switch.

Heres my Non Charging Troubleshooting procedure

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=farmall&th=665110

John T
John Ts Troubleshooting Procedure

rvirgil_KS · May 2, 2009

Your analysis of the field coil connection through the regulator is correct. Voltage feeds the field coils from the armature end of the coil and exits at F terminal to the regulator. The regulator contact is closed, thus grounding the field coil until generator builds sufficient voltage to open the coil, so no voltage will be seen at that point.

To Test: Jumper field terminal to ground. if this makes it charge there is a problem with regulator.

If no charge leave jumper on field terminal and jumper from ARMature to BAT on regulator. If this makes it charge you have a bad regulator, if no charge you have a generator problem.

Here is a link to a Delco-Remy bulletin which explains how the regulator works.

Bob
Delco Remy Voltage Regulator

Anonymous-0 · May 2, 2009

Thanks John T and rvirgil_KS for the good information re: the Farmall M charging system. This is all new to me but from what you've provided I should be able to isolate the problem to the voltage regulator or the generator. I also plan to replace the he generator belt which has deteriorated due to age and engine oil contamination. I'll let you know the result when I get back to it next week.

Owen Aaland · May 2, 2009

Just a slight correction to the circuit description. Since this is a three brush generator, the internal connection of the field coil is to the third brush instead of the A terminal.

It still works the same but, with an adjustable third brush, it is possible to adjust the charging rate by adjusting that brush. Having the brush set too close to the A terminal brush cause overcharging and over heating of the generator. Later generators had a non adjustable third brush.

Anonymous-0 · May 7, 2009

Thanks for the information and tips on troubleshooting my charging system. I was obviously under a misconception of exactly how this thing is designed to work. The weather finally cleared enough to get back to troubleshooting and I found that by jumpering the voltage regulator "F" terminal to ground, it suddenly starts working. According to what you guys are saying, this would indicate a bad voltage regulator. My question is, will any generic two pole regulator designed for a "Class A" charging system (NAPA, AutoZone, Advance, etc.) work here or must I order one specifically for a Farmall Model M Tractor? I want to be sure to maintain the proper charging voltage output.

Also, since the battery provides no excitation to the generator in a Class A charging system, does this mean the generator is "self excited" via residual magnetism? Is this the reason for "flashing" or "polarizing" the generator?

In all my years I've never had to work on a voltage regulator system so it's great to finally understand and appreciate how all of this works. Thanks for your help.

440roadrunner · May 7, 2009

(quoted from post at 21:24:55 05/07/09) Thanks for the information and tips on troubleshooting my charging system. I was obviously under a misconception of exactly how this thing is designed to work. The weather finally cleared enough to get back to troubleshooting and I found that by jumpering the voltage regulator "F" terminal to ground, it suddenly starts working. According to what you guys are saying, this would indicate a bad voltage regulator. My question is, will any generic two pole regulator designed for a "Class A" charging system (NAPA, AutoZone, Advance, etc.) work here or must I order one specifically for a Farmall Model M Tractor? I want to be sure to maintain the proper charging voltage output.

Also, since the battery provides no excitation to the generator in a Class A charging system, does this mean the generator is "self excited" via residual magnetism? Is this the reason for "flashing" or "polarizing" the generator?

In all my years I've never had to work on a voltage regulator system so it's great to finally understand and appreciate how all of this works. Thanks for your help.

The BEST way to order regulators is to get the tag no. off the generator, if there is one. A couple of things that are VERY important about regulators for generators is that

They be the right one, period, if at all possible, because

Some are reversible polarity and some are not--I was told the difference is in the contacts material This deals mostly with the aftermarket In other words, if you get an otherwise correct regulator for the opposite ground polarity, the contacs won't last long

The regulator's job is to limit current from the generator to protect it, I.E if you put a regulator for a great big generator on a smaller generator, you can burn up the generator when the battery is low, because the "big" regulator will allow too much current

Also even Delco had some type A and B systems, so you certainly want that part correct.

Farmall M Voltage Regulator

Anonymous-0

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John T

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rvirgil_KS

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Anonymous-0

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Owen Aaland

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Anonymous-0

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440roadrunner

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