Polarity on IH Super C
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=106215
Printed Date: 19 Jul 2025 at 5:27pm
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Topic: Polarity on IH Super C
Posted By: SteveM C/IL
Subject: Polarity on IH Super C
Date Posted: 15 May 2015 at 9:13pm
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Son-in-law brought home his grandpa's first new tractor. A Super C IH.It was barn kept and in real good condition overall and it runs! 6V battery was low on water so I added some and stuck it on the charger.I noticed it was pos ground like the old AC's.I assume this is correct but would like it confirmed. Guess my 4 Allis's can make room.He's a good kid.
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Replies:
Posted By: VAfarmboy
Date Posted: 15 May 2015 at 10:06pm
Yes that is correct. All of the old tractors from the 1950s that I have ever been around have a positive ground.
Not sure why that is, maybe it has something to do with the generator? Everything we have on the farm built from the 1960s on that have alternators are negative ground.
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Posted By: SteveM C/IL
Date Posted: 15 May 2015 at 10:15pm
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Thanks.Kinda figured so but not sure.
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Posted By: Gerald J.
Date Posted: 16 May 2015 at 9:59am
Design engineers in the vehicular and farm tractor industries didn't agree on polarity, some thought one polarity would corrode the ground connection differently, based on pipe corrosion under DC trolley lines. Actually that pipe corrosion favored opposite polarities if the pipe was near the power plant or distant from the power plant, because it depended on the direction of the current in the soil. And the current from starting flows in opposite directions at the two main ground connections in the vehicle, one being the starter and the other being the ground cable from the battery. So both polarities were used confusing users.
When vacuum tube radios came along for vehicular use, they were not damaged if connected to the wrong polarity, they just didn't work and often were built with easily reversed polarity. In some two way radios, all it took was pulling and reversing the position of the vibrator(s) in the power supply. When solid state radios came along they didn't survive reversed polarity. An instant connection was instant death for the transistors.
In the 50s the SAE standard for vehicle voltage tolerated 6, 12, or 24 volts and said nothing about polarity. About 1955 the standard was changed to prefer 12 volts unless 12 volts couldn't start a big engine but polarity was recommended negative ground. About 1959 the standard changed to require negative ground. That might have been early 60s, its been a while since I looked those up. Deere built positive ground tractors until at least 1969.
Generators could be used with either polarity simply by flashing them to make them build with the polarity to match the battery. Cutouts and regulators often were polarity independent, but some (economically made) cutouts and cutout sections in regulators were made with asymmetrical contacts that had a shorter life when used in the polarity opposite of their designation.
Most common alternators are hardwired negative ground. Even Delcos have been made positive ground, but are relatively rare. At least the Delco book on alternators says there was a positive ground option. No parts store will admit to one. I have a Leece-Neville truck alternator that is not grounded internally, so it could be connected for either polarity. Reversed polarity battery connected to an alternator will cause considerable carnage in the alternator because the diodes are only good for the alternator's rated current while the reversed polarity connection to the battery could cause a short term current of 500 to 1000 amps, limited mostly by the melting of the diodes and the resistance of the charging wires. With 10 to 20 times rated current the silicon junctions melt faster than the fastest fuse and cease to be rectifiers.
Gerald j.
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