Positive Ground Question

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WalkerRO
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Positive Ground Question

Postby WalkerRO » Thu Apr 04, 2024 9:24 pm

Just came home with my second cub. A 1948 serial number 37852. It came with an original IH mower deck installed which works great. Cranks and runs great and all lights work as they should. She is still a 6 volt system with a magneto ignition as indicated by the number 1 wire from the center of distributor to the magneto. It does not charge as it should so started troubleshooting. Noticed the battery is wired for a negative ground system. The negative battery cable.is grounded on frame and the postive cable goes to the starter. I thought a 1948 6 volt system should be a positive ground system. So, why does everything work as it should except charging? Don't want to just change the battery cables to positive ground and mess something up, so thought I better ask the experts. Any suggestions? Thanks much!

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Barnyard
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Re: Positive Ground Question

Postby Barnyard » Thu Apr 04, 2024 10:01 pm

Make it positive ground.
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JohnMihevic
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Re: Positive Ground Question

Postby JohnMihevic » Thu Apr 04, 2024 11:24 pm

As Barnyard said "switch to positive ground" as was originally designed. I also have a 1948 cub with a magneto. I believe this is the best system that IH designed from the standpoint of reliability and simplicity. Mine is all original and still works. Yes, there are not some of the "niceties" of the later systems. However, this a much more reliable simple design -- a cutout relay (no problematic voltage regulator), simple two charge rate system, (Lo=5 amp, Hi=10 amp). This Cub had a "3rd brush" that is adjustable to change the overall (Lo/Hi) charge rate.

If all of the electrical system is original, ie; 3 brush Generator and cutout relay, then definitely switch to positive ground.
When you do this you will definitely have to "polarize the generator" that is explained in many posts on this forum.

Don't worry about changing the battery cables, since you have a magneto (that doesn't rely on any battery power) it is not affected. You won't mess anything up. The only thing I really don't understand is how you can start your cub. The starting motor is a DC motor. When you switch the polarity on a DC motor it will rotate in the opposite direct direction. So, I would expect the starting motor to reverse direction and the cub (engine, bendix spring) won't work under these conditions. Possibly, somebody put a 12V starting motor in your cub, which will rotate your engine in the right direction with the negative ground. But, +6V on a 12 volt motor won't supply much torque -- maybe enough.
John

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Re: Positive Ground Question

Postby k hutchins » Fri Apr 05, 2024 4:56 am

I agree with Barnyard and John. Just switch the cables.

The part l never understood was the need to "repolarize" the generator. In my young and uninformed days, l had wired mine as negative ground. The only issue was that it wouldn't charge. While running the amp meter would swing to the negative side and l didn't know why. It also wouldn't hold a charge and had to be cranked more often than not. After learning that it was supposed to be positive ground, l switched the cables, and no more issues. Amp meter showed it charging, battery held a charge, no more hand cranking required. I never did anything with the generator, and it's been running fine for 30+ yrs.
Why is there never enough time to do the job right, but always enough time to do it over. :?:

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Re: Positive Ground Question

Postby Eugene » Fri Apr 05, 2024 7:17 am

JohnMihevic wrote:The starting motor is a DC motor. When you switch the polarity on a DC motor it will rotate in the opposite direct direction.
The starters are universal motors. Only turn in one direction. Polarity doesn't make any difference. They won't rotate backwards.
I have an excuse. CRS.

WalkerRO
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Re: Positive Ground Question

Postby WalkerRO » Sat Apr 06, 2024 1:12 pm

Thanks to each of you for sharing your knowledge.


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