positive and negative ground

[sp53]

Hi all I have a question on positive and negative ground. I remember my auto shop teacher in 60s saying that a spark jumps from hot to cold 10% better so it is better to have negative ground. However, I think he said that positive grounding systems are better because when you go to gas station the spark would not jump off your car onto the nozzle. Is that right?
Steve

 

[TR3driver]

The polarity of the spark at the plugs has nothing to do with which side of the battery is grounded. The coil will cheerfully produce a negative spark even on a positive ground car.

And while the difference depends somewhat on conditions, I believe it's much smaller than 10%, just a few hundred volts out of 10,000 or so. It also has no effect at all, as long as your ignition has the margin to cover it. Many engines even run half the plugs "backwards", as it halves the number of coils you need for a "distributorless" ignition.

Never heard the one about battery polarity having anything to do with static electricity; but it sounds like bunk to me. There have been lots of other theories advanced as well, but none of them proved to have any practical significance.

Bottom line, the only real advantage to negative ground is that 99.9% of the vehicles on the road today are wired that way, so 99.9% of the devices and accessories available are designed for negative ground. Even Mack finally succumbed to the pressure to conform, some time in the 70s I believe.

 

[Guest]

Ahhhh..... Mr.Science questions can be lots of fun. Throw in shop teachers from the 60's and probably a little Jack Daniels and the possibilities are endless.Positive or negative ground. It be or not to be? That is the Question.I was sitting a bar and an electron sat down next to me and ordered a beer.Being the kind or bar that usually didnt get many free electrons wandering in,my curiosity got the better of me. Owning positive ground British cars,I had to know his opinion on the subject. Which was better and why? He told me it really didnt matter. Push me or pull me,Im a pretty easy going kind of guy,as long as I end up where I started,at the battery. He said that his generator buddies,the bosses, were easier to get along with,because they could change polarity,just like their socks. Their alternator cousins,are a lot harder to live with,even thought they put out more power.He said it was that diode thing,that held back their flexibility.That AC/DC thing and I told him it wasnt that kind of bar.I thanked him for his expert opinion and bought him another beer. He told he was shocked and being an electron,I took his word for it. As for the 10% thing,I kind of doubt it. Exploding cars? Kind of doubt that too, but when filling a gas container,always place it on the ground to eliminate static electricty. Most car owners switch polarity to use negative ground accessories,radios and modern alternators.Originality-positive ground. Modern updating-negative ground. As your shop teacher always said" HEY!! Quit screwing around! Hope everyone knows Im just having fun.

 

[TexasKnucklehead]

The direction of the spark (from the nozzle to the car, or from the car to the nozzle) would have the same explosive results.

But, I always put the positive lead on the battery first, followed by the negative. The spark on the negative side is suppose to pull the terminal to it. Plus, it's much harder to short out the hot side while tightening, because there is no relative ground.

 

[TomMull]

"But, I always put the positive lead on the battery first...Plus, it's much harder to short out the hot side while tightening, because there is no relative ground".
This is what I was told also, except in this context, would it be better to say to put the hot lead on first and the ground last?
(The spark pulling terminals is news to me, but I'm no physicist)
Tom

 

[rlwhitetr3b]

Tom got it said first...
The positive first thing only works on negative ground cars. One positive grounded it would be negative first. I.E. you do not want the body of the car connected to the battery until you have everything else ready to go.

 

[Roger]

Electrons travel from negative to positive, regardless of what your diagrams may say.
Having said that, it all depends on what you want to rot first, your body or your circuit.

 

[sp53]

Thanks all for your thoughts. Yes I think they were all drinking Jack and we were watching the orange sunshine. My first car was a 54 Ford Vicky and they came positive ground. So we talked more about that stuff then. The teacher was this real smart guy, and if I remember the theory correctly, it was kinda what Roger was maintaining. The teacher talked a lot about lighting and static electricity, and well at any rate, I guess some lighting actually goes up and other lighting goes down and perhaps the static electricity created by the moving vehicle if the car was positive ground would let the spark jump back to the car ??????? Hey it was the sixties.
Steve