Farmall H 6 Volt Voltage Regulator - Resistor on F

With the help of John Nordhoff's excellent Non Charging Troubleshooting Procedure obtained in a posting in this forum, I have isolated the non-charging issue (I think) with my 1949 Farmall H to a failed resistor which is in series with the field terminal on the 6 volt 4 wire voltage regulator.

When I grounded directly from the field terminal on the generator to the tractor frame, and after polarizing with engine running by briefly jumpering from Armature post on generator to BAT terminal on regulator, a small spark was seen and charging rate of ~10 amps was indicated. Removing the direct ground results in complete loss of indicated charge. A charging state cannot be obtained by directly grounding the regulator saddle bracket to the tractor frame. The resistor believed to be the problem is marked "1 ohm - NEXCOR - 9650", but a check across the resistor with a multimeter indicates an open circuit rather than a small resistance. My conclusion is that the generator is OK, but the regulator (specifically the resistor) is the culprit.

My question: What are the potential negative impacts of simply removing the 1 ohm resistor and attaching the wire directly from the generator field terminal to the "F" lug on the regulator (without the 1 ohm resistor in between.) As can be seen by examining the rightmost terminal in the attached photo, this would result in a direct path to ground from the generator field post.

Alternately, if the resistor is necessary, where might one look to find a replacement? If available, it will certainly be more cost effective to replace the resistor than the entire regulator, but it is often difficult to come by small replacement parts such as this.

Another issue I am dealing with is that all that is available locally is a 3 wire regulator. I am replacing a 4 wire unit, and I would prefer to avoid a rewiring exercise to run lights from the ammeter output rather than the "L" terminal on the regulator.

Thanks!

Thanks for the helpful comments.

As it turns out, my problem was dirty contacts on the voltage/current regulating contacts in the regulator. Basically, the electrical continuity between the field post on the generator and ground was disrupted, even when the contacts were closed. After I cleaned the contacts and polarized the generator, normal charging function returned. This is consistent with the fact that I was able to get the generator to charge when the generator's field post was directly grounded to the frame, but not when hooked up to the "F" lug on the regulator.

I did experience a bit of frustration during this process due to a botched polarization process. On my initial attempt I did not run a temporary ground from the generator field post to ground when I briefly jumpered from "A" terminal on generator to "BAT" lug on regulator, and this did not work; I had to ground directly from "F" post to frame to sucessfully polarize. I suspect this is due to the high freqency opening and closure of the regulator current/voltage contacts which occurs during normal operation of the contacts.

Interestingly, before polarizing properly, the cutout relay contacts did not function properly either. With the engine off, the normally open contacts stayed stuck together! There was not enough electromagnetic force to draw the contacts together after they were manually pulled apart, but there was enough to hold them together if contact was made. I believe that during normal operation the direction of current flow from the battery acts to "push" the contacts apart electromagnetically to aid in a "clean" disconnect; current flow in the wrong direction would have exactly the opposite effect and pull (or stick) the contacts together. I do not fully understand this, as I do not quite "get" the whole polarization thing, but it certainly seems to enter the equation. After polarization the cutout contacts separated normally when the engine was shut off.

The generator P/N is 1101355, and the comments make sense that the power resistor on the regulator replaces the (no longer used) shunt resistor on the 4 position switch which is on the tractor to limit the field ground and thus the charging current. Sounds like a good idea to keep the resistor in place to avoid potential problems. The resistor was not the issue or defective; the incorrect assumption that the I had electrical conductivity through the contacts took me down the wrong logic path.

An excellent discussion which was very helpful in understanding the generator and regulator operation was found at>Link

Again, many thanks for sharing your knowledge.

If one has a 4 pole (BAT ARM FLD LOAD) versus a 3 pole (BAT ARM FLD) Voltage Regulator, I would use the 4 pole cuz they supposedly provide better regulation,,,,,can better prevent overcharging in certain situations,,,, and dont have to run all the load current through the cutout relay. If using a 3 instead of a 4 pole VR, loads like lights and ignition (fed off the L terminal on 4 pole VR's) are fed from the ammeters Load side terminal which would be the electrical equivalent of the BAT terminal on the VR like Bob M told you.

If you wanna buy a replacement field resistor it needs to be a high power (often wirewound) unit which a good electrical supply house (maybe NOT Radio Shack???) ought to have. A 15 watt ought to handle it.

John T

If you replace the 4 terminal regulator with a 3 terminal, simply connect the wire that went to the "L" terminal on the old regulator to the "B" (or "BAT") terminal on the new one. (You"ll now have 2 wires on the new regulator "B" terminal...)