Farmall Cub

Hi fellas (And ladies? Hey why not? ): Seems quite a few threads comment on the idea that those that pull their battery out and put it back in with the terminals wired backwards is a common occurance. It also seems that the tractors normally start and charge fine and it's only pure happenstance that they notice the backwards configuration; typically when they see the ammeter showing discharge when it is in fact charging. Then they get all worried and come here and the pros say, "Hey, go get a and chill." lol So why is it that the tractor can charge the system and run normally with reversed polarity even when they have a voltage regulator that is for a "positive ground" electrical system? If the voltage regulator "didn't care" abut polarity, why are they labeled as if they are polarity sensitive?

I ask because my tractor is now positive ground but as some may recall from an earlier post that I have a funky 6 volt positive-ground voltage regulator that is making my 6 volt battery nearly 9 volts . The last thing I want is to damage my battery or worse, cause and explosion or fire. As always -

Not sure about the theory behind it, but I do know that regulators (at least the 6v ones) need to be properly polarized to charge properly. These regulators can be polarized for either positive or negative earth. So maybe the label on the box merely indicates how the VR was polarized at the factory?

I believe it is the generator that gets polarized, not the regulator. I have no earthly idea why they specifically mark the mechanical relay used with the Cub as 6 volt positive as the polarity should make no difference and I have seen them run either way.

My voltage regulator on my '54 is presumably from an old Model A and not for the Cub. It is a 6V positive ground unit and the consensus is that it should still function for the Cub. It also has only two terminals on it and responses to earlier posts indicated the configuration means it is always at full charge. Presuming this unit will work even though the polarity is reversed, can it be adjusted somehow to reduce the charge rate?

If anyone has any other ideas as to its polarity rating I'd love to hear (read? lol) your thoughts. It baffles my mind that they're listed as being for a certain polarity but work either way.

Your "voltage regulator" with two terminals would indicate that it's a cut out as opposed to a voltage regulator, which has at least 3 terminals.

It's quite possible that your "voltage regulator" cutout is polarity specific to activate the shunt winding (battery disconnect).

If you have a cut out, it was frequently used with a 3 brush generator. To adjust the voltage out put on a 3 brush generator you need to move the adjustable brush.

Eugene wrote:Your "voltage regulator" with two terminals would indicate that it's a cut out as opposed to a voltage regulator, which has at least 3 terminals.

It's quite possible that your "voltage regulator" cutout is polarity specific to activate the shunt winding (battery disconnect).

If you have a cut out, it was frequently used with a 3 brush generator. To adjust the voltage out put on a 3 brush generator you need to move the adjustable brush.

So am I correct that I'm not going to be able to run this tractor with negative ground if my cutout is in fact polarity sensitive? Even if I could adjust my generator the cutout will not function properly in this configuration, yes?

Connecticut Calvin wrote:So am I correct that I'm not going to be able to run this tractor with negative ground if my cutout is in fact polarity sensitive? Even if I could adjust my generator the cutout will not function properly in this configuration, yes?

I don't know and may be. I don't know how your "regulator" "cut out" is wired or which regulator/cut out you have, so I could look it up. I also do not know which generator you have. K.I.S.S. If the cut out/regulator says positive ground - make the battery positive ground.

Your original post said "regulator" and "nearly 9 volts". Determine the number of brushes in the generator. You need to reduce the generator output voltage by about 1 to 1.5 volts.

Eugene wrote: Your original post said "regulator" and "nearly 9 volts". Determine the number of brushes in the generator. You need to reduce the generator output voltage by about 1 to 1.5 volts.

Regulator / cutout, what do I know? In prior posts it seemed no one could pinpoint what I had either. But a cutout sure seems accurate. I really liked the idea of keeping the tractor negative ground but this no longer seems like an option. I have some higher priced LEDs that will blow with this kind of voltage and who knows what will happen to the battery. Looks like I'll have no choice but go back to positive ground and use standard incandescent bulbs. I'd rather not risk any damage to the tractor for a set of bulbs. I'll consider this topic a moot point. Thanks for guiding me to the light of reality! No pun intended.

The neg./pos. designation on the regulator has to do with the dissimilar metals in the regulator contacts. The arm is a different alloy than the fixed contact to reduce contact arcing, those alloys will be positioned in one configuration for pos, ground and in the reversed config. for neg. ground. The regulator (or cutout) will function the same in either neg. or pos. ground but when a pos. ground unit is connected neg. ground it will have a shorter life span.
As to your overcharging, look again at what Eugene posted about the 3rd brush. That was the method of limiting generator output on earlier units.

That said, a "positive" regulator or cutout will work with negative ground, just maybe not as well, or not as long, as if it were wired properly. Maybe.

My theory on the whole thing is it's a little "subliminal message" to reassure people that they have the appropriate part, even though it doesn't make a hill of beans' difference one way or the other.

It's like the 6V vs. 12V "ballast resistor required" ignition coils. If you go to an auto parts store and ask for an ignition coil for a vehicle with a 12V ignition system from the 1960's, you will get a coil labeled "12V ballast resistor required." This 12V coil is no different from a 6V coil. It's just labeled 12V so people don't get confused.

Okay well ol' Betty is back to negative ground. I switched the coil wires and the + wire is now going to the distributor cap, reversed the ammeter wires and reversed the battery cables. I'm getting about .25 amp charge at idle, .5 amp charge at mid throttle and a little over a single amp at full throttle. Let's hope this solves my issue. After an hour's use today and a few starts and stops my battery is holding steady at 6.75(ish) volts. Perhaps my cutout is OK and it just didn't like the way my wiring was done. Oh well, so long expensive LEDs. It was nice knowing you! Anyone want nice, unused 6v NEGATIVE GROUND LEDs for their machine PM me! I have 4!

All great input gents. Thank you.

Put them in the classifieds with pictures!

danovercash wrote:Put them in the classifieds with pictures!

Posted!