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Farmall A generator

D

dahlin

Member
We have a 1940 Farmall A with a magnito. The generator has 1 wire coming out of the voltage regulator. The P.O. put the battery in with negative ground. I would like to switch it back to a positive ground. Whats the procedure to do this? Just switch the battery cables, or do I drain the battery first? Does the generator need to have its polarity switched also? Thanks for your help. Randy
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Several small steps, all pretty simple.

First thing to check is whether you have a cutoput relay or an actaul voltage regulator. If the relay leave as is. If a regulator, you need to give it a look -- some work with either ground, some are built polarity specific. If a regulator made for neg ground you'll need to change it out.

Once past that it's all easy. Swap the wires on the terminals on the back of your ammeter so your needle will move the right way when charging. Swap the cables on your battery (NO need to drain it), then repolarize your generator, which is as simple as making a quick connection between the BAT and GEN terminals on the relay/regulator.
 
NOOOOOO you dont drain the battery, its still a battery with a + and a - terminal REGARDLESS which post just happens to be bonded to a huge chunk of rusty old iron......

A genny can still charge a battery, again REGARDLESS which post is tied to the tractors frame and whether one uses that frame as a return current carrier wired to the + or - battery post.....

That being said, if you want to reverse battery polarity by changing which post you tie to frame ground ( + or -) all you do is reverse the battery THEN BEFOREEEEEEEEEE YOU START THE TRACTOR POLARIZE THE GENNY by using a lil jumper wire etc to momentarily flash/jump from the BAT terminal on a Cutout Relay or a Voltage Regulator over to its GEN/ARM terminal and you should get a spark. THAT ANSWERS YOUR QUESTION YESSSSSSSS YOU SWITCH GENNY POLARITY BY RE POLARIZING IT AS ABOVE

If it has a working ammeter (and you change battery polarity) its leads need swapped or else it reads bass ackwards.

Got it??????????????

John T
 
The tractor might not have one but after changing the polarity wont the starter run backwards.

I know the starter can be changed also but it has to come apart.

Just something else to think about, if it has an electric starter.
 
There's a name (which escapes me just now) for the type of motor that the starter is, but it will turn the same direction regardless of polarity. Good thought, but . . .
 
NOPE even if you change battery polarity the tractor starter STILL TURNS THE SAME DIRECTION REGARDLESS.

Tractor starters (usually series wound) utilize a wound electromagnetic field versus small lawn tractor starters that use permanent magnet fields. A small permanent magnet motor will indeed change direction if you reverse its electical connection polarity butttttttt to reverse an electromagnetic field starter you have to reverse/swap EITHER the field or armature windings......i.e. you have to change the relationship of the field versus armature (push/pull attract/repel) and if you just swap electrical polarity they dont get changed with respect to each other STILL TURNS SAME DIRECTION

Clear as mud????????

John T
 
Scotty, thats a wound Electromagnetic Field (big tractor starter motor) versus Permanent Magnet (PM) Field (smaller cheaper lighter lawn tractor starter) You just had a Senior Moment, you will get them more as you grow older lol

John T
 
That one wire thing has me wonderin' if everything is hooked up okay.

Right arund the generator, you should have one short wire between the A(rmature) stud on the generator to the GEN terminal on the relay. If there is only one other wire from the front to the rear, it should be from the BAT (not the FLD) terminal to your ammeter. From the factory they came with a second wire front to rear, that ran from the F(ield) stud on the generator body to the 4-position light switch, where the operator could select high or low charge rates in addition to dim and bright lights. You will occasionally find (and there are instructions in the Operator's manual for it) that the wire from the F(ield) stud on the generator could be snubbed off and run directly to ground at the front end to give a constant high rate of charge.

Bottom line, check your wiring out and see what you have there. Your ammeter may be fine.
 
There's a wire that runs from the battery side of the cut-out. Then there is a another wire from the stud on the generator, it looks like it runs from the screw on the cut-out. There's another wire that comes out of the body of the generator. It runs from the other terminal of the cut-out.
 
Best look at it from scratch. You might have to clean up the shell of the genrator to find the A and F marks on it indicating the armature and field studs. You may only find one of them - marking was sloppy.

One short wire from the A(rmature) stud on the generator to the GEN terminal on the relay.

Then one long wire from the BAT terminal on the relay to the ammeter.

The F(ield) terminal on the generator will have to be hooked to something that grounds. Your choice. If you have the four position light switch, run directly from the F(ield) terminal to that. Run the wire right alongside the one from the BAT terminal to the ammeter. This will give you the option of selecting a high or low charge rate with the switch. (High charge runs straight through to ground, low charge passes through a resistor on its way to ground).

At the very least, if you decide not to run the long wire from the F(ield) stud on the generator all the way back to the switch, you will need to have a short wire from the F(ield), grounded on the other end to one of the bolts on the gene4rator mount, which will give you a constant high rate of charge.
 
Thanks, I learn something new today.

I know enough about AC and DC motors to work with them when given the correct diagrams and be a little dangerous beyond that.
 
Thanks Scotty, I think with the field being grounded to the screw on the cut-out and the armature running to the other side and battery terminal running back to the ampmeter is the way it is hooked up right now. I think I'll just leave it like this. Thanks for walking me through this. Randy
 
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