Years ago, it was called either "conventional flow" or "electron flow". My understanding as to why we are vehicles made in the last 50+ years or so with negative ground was for uniformity in the industry, at least with the Big Three. May have been mentioned before (I saw a question asked) about reversing DC motors. Permanent magnet DC motors can be reversed by switching the leads. DC brush motors can't (to my knowledge).
In order to reverse rotation on a dc motor you have to reverse either the armature or the field, but not both. When you reverse the polarity of a starter you are actually reversing both, so it turns in the same direction. On old power windows you reversed the field current but not the armature current. This caused the motor to reverse direction. Newer power window motors have permanent magnets for the field so you reverse the armature current. Also, turning the brush plate on a starter motor 90 degrees wouldn't have any effect on rotation on any starter motor I ever saw.
The Model T was negative ground, no? I've heard the corrosion theory about why the switch was made to negative ground. That doesn't make any sense either. As far as uniformity, they were (mostly) positive ground. They were already uniform. Something something about the way then-new transistors (diodes?) are grounded to the case, that sort of makes sense. Alternators were coming in big, or were about to, they needed lots of juice to power all the new accessories that were becoming standard, generators weren't up to the task.
Think I read someplace that the British observed that with the old cloth wrapped wires that were the norm, especially in the damp, that Positive Earth systems had less loss, leakage, drain (whatever) in the system. This was the perceived advantage. Experts?
So your basic and "advanced" electrical schooling at Ford in Carrolton taught you about the parasitic drain thing? That's just some really poor damn training. A DC starter motor in our old vehicles is a "series wound" motor, meaning that current flows through the armature and field in a single loop. Because of that, the relationship of the magnetic fields in the armature and field windings is the same no matter what polarity is applied. So if you change a vehicle from positive to negative ground the series wound starter will still spin the engine the proper direction. If you have one of those new-fangled permanent magnet starters, they will run backwards if the polarity is wrong.
->>> and corrosion where the current leaked through the insulation to the metal body/frame I was told, and did some research, that it was due to the poor insulation of the wiring 'back in the day' EVERY ACD car we have in the collection is 'Positive ground". It seems to me that everything was positive ground until 1953-54(?) I am sure there might be a few exceptions
The advantage to disconnecting the negative terminal of a battery (in a negative ground car) is that if the wrench that is being used to loosen the terminal hits some other part of the car, there isn't a huge spark. Maybe that's why the school training emphasized taking off the negative connection, and someone along the way came up with the other reason using the logic that students would care more about a discharged battery than safety.
What always seemed weird to me was the fact that GM made vehicles both ways. For instance, AD trucks: 6v Chev was neg ground, same truck (mostly) with a GMC badge was pos.
I gotta agreed with you on this one. I read years ago that Henry Ford believed that with a positive grounded body and frame, nuts and bolts would vibrate clockwise (tighten) from road vibration...negative ground would cause them to turn counter-clockwise and loosen up from road vibration.
"What always seemed weird to me was the fact that GM made vehicles both ways. For instance, AD trucks: 6v Chev was neg ground, same truck (mostly) with a GMC badge was pos." See, Ford isn't the only one with weird feces!
Actually, an American named Robert Kearns invented the intermittent windshield wiper. He patented it and Ford and Chrysler stole it from him. Robert Kearns, 77; Invented Intermittent Windshield Wipers. Robert Kearns, the inventor of intermittent windshield wipers, who won multimillion-dollar judgments against Ford and Chrysler for using his idea, has died. He was 77.Feb 26, 2005
if we're not confused enough-I'm told on an 8 cyl magneto,such as a Vertex-4 of the plugs are firing negative ground,4 are firing positive ground?
Really do appreciate all the answers and your time but has the question been answered Why are some engines/vehicles positive grd and some neg grd ?
Some are positive ground and some negative ground because the designers had to choose one of the two options.
Ah, the Chebbrainwashed make an appearance. Do you seriously think Ford was the only manufacturer to use positive ground? C'mon...
The reason, that I read, why they chose positive ground over the now popular negative ground, had something to do with corrosion. I can’t tell you the exact theory they employed on this positive ground thing, but it was supposed to have less corrosion. Or it could have been like Mike51Merc said.... they may have just flipped a coin! There is no “ huge” advantage of either positive or negative ground, but it does have to have one or the other! Bones
If you make a DC electrical system in a car and let the frame, body etc. get connected to the electrical system as ground you need to choose if it should be the positive or the negative side. Nothing prevents you from completely insulating the system so the body etc. isn't connected at all, but as it may be simpler to let things like the starter motor, generator, lamps, temperature sensors etc. be grounded straight to the metal they're attached to than running another wire to every single one of them it makes sense to have the entire car be a working part of the electrical system. Especially if you make a million cars a year and don't want to put another 20 yards of expensive copper wire in each car when there's a ton of perfectly good steel that in many cases can do the same job already there in the car. Why positive or negative? Flip a coin, pick one and run with it. They both work. In electronics you often have a "double voltage", where your audio amplifier for example can run on a total of 64 volts, divided into +32V and -32V, with a 0V ground/neutral in the middle. As you want electricity to the speakers to be able to go both ways to make the speaker move both ways it's a simple way to make it work. Hook one speaker cable to the neutral 0V and the other to a lead that can give anything between +32 and -32V. Starting from a single 64V supply w/o a center outlet would make it harder to build a good amplifier - perhaps not so much with modern electronics but for sure with more basic stuff.
Weps has nailed it. Back in the really old days there was no plastic, and wires were insulated with all kinds of poor **** like natural rubber, cotton, and sometimes even paper or cloth. Electrical leakage was a big problem, especially if your ****py wiring became wet. Electrical leakage meant CORROSION from ion migration. (rather like electroplating) except with a negative ground its your wiring that gets eaten away. With positive ground its the vehicle frame that gets eaten away which is much less serious, because there is more of it. Anyhow, time marches on, we went from 6v systems to 12v systems, wiring became of much higher quality and negative ground became the more usual standard. Telephone exchanges also used to be -50 volts for the exact same reasons, the ancient paper insulated lead sheathed underground cables lasted longer, and right up to today's fiber optic broadband, just about all telecoms equipment was positive ground, and much of it still is.
I was going to jump in on the electrical theory discussion, but I can't stop chuckling over the Lucas jokes...
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