|
| I've made extensive posts over on the unofficial Allis Chalmers page in the past three or four years on the topic.
Basically there are two ways to use the chassis for ground in a DC system. Positive ground and negative ground. They both work. The differences sometimes confuse amateur electricians of equipment, but shouldn't so long as there's attention to connection the battery correctly which is why the battery has one FAT post and one thin post. Usually the FAT connector won't clamp on the thin post and the thin connector won't go on the FAT post without considerable hammering.
Then the 4020 and 3020 diesel (and some diesel two cylinder tractors) used both with a floating 24 volt starter and generator. That's even more confusing to amateur electricians.
There were also arguments between DC trolley companies and water companies about polarity. Seems the water pipe was a better conductor than the earth and where electrons left the pipe they took metal with them corroding holes in the pipe. So a water pipe near the power plant was preserved by one polarity and damaged by the other polarity while at a distance from the power plant, the polarity for pipe preservation was opposite. So the arguments were never really solved.
I suspect the same arguments were applied to vehicular batteries and the ground connections at the battery cable or the starter when electric starters became factory options. Thing is only the ignition coil polarity and ammeter polarity are affected by the battery polarity and then the engine still ran with the reversed polarity, just not quite as good for the ignition and the ammeter reads backwards. If flashed the generator doesn't care, the lights don't care, and the starter doesn't care. Today the computer, the alternator, and the radio don't survive a millisecond of reversed polarity.
I've looked up SAE standards and their history on battery polarity, but I don't remember the details that I've posted in the past few years on the AC site. Seems like it was long about 1957 when SAE began to recommend negative ground and 12 volt systems. It was about 1960 when SAE changed that standard to say SHALL be negative ground. It took a while for the tractor, truck, and automotive industry to follow the revised SAE standard because JD 4020 gas and LP were positive ground until at least 1968.
Somewhere I think I have book of reminiscing by an electrical engineer that had an article from an electrical journal in the 1930s on the origin of positive and negative DC vehicular grounds. I recall it also has an article on the choice of frequencies for AC power, but I've not seen it in my house for years, and two years ago I moved and lots of books are still in boxes, some I packed, some the movers packed. There's a chance I loaned the book and it never returned or that it was under a pile that wasn't disturbed until I moved.
Gerald J. | |
|
Positive ground question.
