6v vs 12v and positive and negative ground

WD40er

New User
Just bought a 1952 TO 30. Seems pretty stock in appearance. I'm confused on the 6v and 12v battery systems. The owner said it was 6v and battery had died recently and he stuck a 12v battery in it to start it up and put on the trailer to deliver to me. Once at my house, he cranked it up and drove it off the trailer into my yard and seemed just fine. I'm confused as I thought a 6v system was positive ground and 12v was negative ground. I took the battery out after he left just to be safe. I was under the impression that putting a 12v battery into a working 6v system would blow the battery or start shorting things out. Any help and comments and suggestions would be greatly appreciated. Knowing beforehand that the tractor was a 6v I had ordered the 12v conversion kit offered here and it's supposed to arrive next week. But I'm confused as to how it worked with him putting in a regular 12v battery already and the tractor seemed to run fine. It still has a generator.
 
Generator systems are not sensitive to polarity. They can run either way as long as the generator is polarized accordingly.

What he die was just a temporary install to get it running long enough to move it. The battery would eventually discharge as the generator and regulator are set up for 6v use.

When you get the conversion kit installed, the battery must always be kept negative ground, as an alternator is sensitive to polarity.

You will also need to reverse the coil polarity, the - terminal to the distributor, the + terminal to the ign switch. You will also need to add a 1.5 ohm resistor ahead of the coil, or replace the coil with a 12v, 3 ohm coil.

Any lights will need to be converted to 12v.

Be gentle with the starter. It will still work on 12v, just be careful not to crank too long as it will overheat. Also be careful when engaging the starter. Be sure the engine is completely stopped, and the starter has coasted to a stop before engaging it. They are known for breaking the starter nose cone.
 
Thanks for the all the info Steve...the info on taking it easy on the starter is duly noted. Question, I have a bunch of old 12V coils in the garage from small block chevrolets. Would one of these be ok to use?
 
(quoted from post at 04:57:27 04/12/18) I'm confused as I thought a 6v system was positive ground and 12v was negative ground.

Just to clarify. It is generator systems that are normally +ve ground, whether 6 or 12 volt. It is the alternator that demands -ve ground.

Your Chevy coils could work. Use a meter to confirm that they are about 3 ohms, or they would need the resistor too.
 
That is not entirely correct, alternators produce 3 phase AC, there is a rectifier bridge mounted in the alternator that converts AC to DC, so the orientation of the diodes in the bridge set the polarity of the alternator. The regulator, wether alternator or generator, if mechanical, probably does not care, a solid state regulator will care, as there are transistors and diodes in there that will burn out if reverse biased.
 
Positive and negative ground is like right hand and left hand threads on a bolt. With bolts, the nuts turn in opposite directions. With grounds, current flows through the system in opposite direction.

Generators can run either polarity, but some regulators are marked for positive or negative ground.

Any alternator that you are likely to encounter was built negative ground. If it is now positive ground it is likely one that has been specially modified.

Just because tractor came from factory as positive ground does not mean it must stay that way. If properly configured it can run on negative ground, even with 6 volt generator.

The only things on these old tractors that care about ground polarity is the charging system, the coil, and the ammeter. (Also electric fuel gauge, but they did not come until later.) Only part that is critical is charging system. Ammeter will work either way but will indicate backwards if polarity reversed. Coil itself doesn?t care about polarity but spark plug can and coil is marked to give greater plug efficiency. Engine will run either way.

Running the tractor for extended time, the 6 volt generator could discharge the 12 volt battery. However, your regulator is likely defective and if so would prevent battery from connecting to generator.

The Chevy coils would likely work if matched with a resistor that would run the ignition circuit at about 4 amps. They are likely designed for a resistor in series with the coil that is bypassed when the engine is cranking. Try and find a coil with 3 ohm resistance across the + and ? terminals and use without a resistor. If you need a new one, ask for NAPA IC14SB or equivalent.

Check any resistors that may come with your conversion kit. I?ve seen kits that came with incorrect resistance for the system. If it is not close to 1 1/2 ohms don?t use it. Don?t use it with a 3 ohm coil.
 
Thanks all....cannot say that I'm not still a little confused as to how it worked without either shorting out the ignition switch etc if the 6v system was positive ground. (since the wires Sorry I don't have pictures to post as of yet of the current configuration. But when I disconnected the 12v battery he had put in it, I did notice the negative cable was attached on the other end to the tractor frame. It was a metal braided line. As mentioned earlier, the conversion kit is to arrive next Tuesday and it will become somewhat of a moot point once installed. But I do like knowing the why's and hows of it anyway. One question, what exactly is meant by the term positive ground? When the former 6v battery was installed, does it mean that braided ground strap was connected to the positive terminal of the battery?
 
?One question, what exactly is meant by the term positive ground? When the former 6v battery was installed, does it mean that braided ground strap was connected to the positive terminal of the battery??

Yup, positive or negative ground designates which battery post is designated ?ground? in the system.

Batteries are connected with one post being the ?supply? or ?hot? post and the other being the ?return?, or ?ground? post. The electrical system can be designed to be configured either way.

The supply post connects to power the separate circuits ? charging, ignition, starting, lights. The ?ground? completes the circuits back to the battery.

With ?positive ground? the positive is the return post. With ?negative ground? the negative is the return post.

For convenience the ?ground post? connects to the frame. The battery post is the actual ground, the frame is just a big ?extension cord?, it uses the frame in place of multiple wires back to battery post.

The ?ground? is also the zero reference point for taking voltage measurements.
 
(quoted from post at 06:24:58 04/12/18)

Just to clarify. It is generator systems that are normally +ve ground, whether 6 or 12 volt. It is the alternator that demands -ve ground..

In saying "generators are normally +ve ground", I mean from the factory. You could run into a tractor that is modified, of course. The big advantage of leaving it as original, when you go back to the manual for repairs, the schematic is correct. Without having to switch the ground from +ve to -ve in your head.

I have one 6 volt, +ve ground tractor and one modified(by previous owner) to 12 volt -ve ground with alternator. I have to constantly remind myself which one I am working on.
 
My Oliver 88 had a 12 volt battery hooked up as positive ground but the 6 volt generator wouldn't keep it charged.Everything worked fine. I
had the generator converted to 12v negative to keep it looking original.Just put a resistor in leading to the coil. Starter is still 6 volt.
 
The Chevy coils will also need a resistor.

You can just keep your original coil and add a resistor to it.

The conversion kit should come with a resistor.
 

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