Re: Here's what confused me, fellas.

Posted by Gerald J. on February 16, 2007 at 19:10:31 from (67.0.103.250):

In Reply to: Re: Here's what confused me, fellas. posted by hillbillyOH on February 16, 2007 at 12:50:40:

There are left handed folks and there are right handed folks. There are negative grounded batteries and there are positive grounded batteries. Both function perfectly well. Neither is wrong, though for at least the first half century of automotive and tractor electric systems there were adherents to each polarity and each had technical arguments they felt valid.

There are and were also DC trolley systems of each polarity. Depending on the relative locations of underground pipes with respect to the power connections to the trolleys and tracks, one polarity was better than the other at protecting those pipes from electrolysis. Sometimes that same argument was applied to automobile battery polarity.

And there have been tractors with one of each polarity, the JD diesels with electric start from the 50s though about 1969. They had a 24 volt system with the mid point grounded. Starting and charging didn't use ground, just 12 lighting loads but there had to be two 12 systems, one positive and one negative to keep those loads balanced so the 24 volt charging would charge the batteries equally.

Very many 6 volt tractors had the positive grounded. My gas 4020 though 12 volts had the positive grounded. With a generator it wasn't critical, so long as one polarized the generator when it hadn't been run in a long time and connected the ignition coil for the same polarity as the battery. It wouldn't run quite as good with reversed coil polarity.

With solid state, as in the rectifiers for alternators, solid state ignition and radios, polarity is a bit more critical. The wrong polarity destroys the solid state parts faster than the fastest fuse can blow. In the early days the radios were made with switches to set their polarity, even vacuum tube radios needed that. And while MOST alternators are made for negative ground, its possible to make them for positive ground or no ground at all and they are made those ways, but aren't common.

Gerald J., electrical engineer from Iowa

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