ShopTalk Forums | Aircooled VW Tech & Restoration Help

Wow, there's a couple rooms full of idiots. I can't believe they're seriously concerned about ill effects of a positive-ground car colliding with a negative-ground one! This isn't matter vs antimatter, for chrissakes.

It matters not one whit whether the chassis ground is negative or positive, either arrangement works exactly as well. The only reason for the switch to negative ground was to join the rest of the world and allow the use of common accessories (specifically, radios).

In order to form a complete circuit, whether it be AC or DC, there must be a return path to the power source. Even radio waves, which emanate from the broadcast aerial, have some of their energy returned through the atmosphere and earth. But in a DC circuit you want the return path, whether it's via discrete wire or through the conductive chassis (or car body) to be capable of handling the same amount of current that the supply side needs to produce. But that's the maximum it will ever carry, it can't do any more "work" than the supply side asks of it.

Electricity was discovered long before anyone had a way of determining which way the electrons flow; the pole with more electrons present was declared "negative" and the other one "positive", and to this day we still speak of "conventional" current flow as being from positive to negative - even though the convention was incorrect insofar as the actual flow of electrons, which is from negative to positive. Even the circuit symbol for a diode was devised based upon "conventional" current - its arrowhead points against the actual electron flow.

Unless you're designing electronics components it's not really that important anyway. It's bad to have your ignition coil hooked up backwards because sparkplugs function more efficiently when the center electrode is negative (the high-voltage out of the coil is a negative pulse) but beyond that it's not something that the average mechanic needs to understand beyond the realization that every circuit needs a return path.

Oh, it should be pointed out that electrons do flow from positive to negative inside the battery or dynamo.

Here's an indictment of the educational system in our country that I find amusing. Bear in mind that these kids have paid over a quarter-million dollars for their Ivy League degrees: http://www.youtube.com/watch?v=8ve23i5K334

I couldn't watch more than the first minute.. it was too embarrassing! Remember; I lived with this for 34 years. After working with personnel/HR when I was teaching for the company and doing other things I was told that the only thing a degree got you was an interview (it was figured that if you could finish your education and get your degree that was one thing). The diploma did not tell them if you learned/retained anything or if you knew what to do with or how to use what you had stuffed into you... the first 6 mos. to a year would give them an idea of the person. Cruel but that is how it is. I worked with several engineers who were nice people but who did not have a clue on how to be creative or use what they had in their heads.

The write ups I posted said that there were some early on assumptions made about electron flow that some people have carried on and you see it even today.

I'm sorry I even lightly pulled on your chain but I just couldn't resist but the results are a positive I think (my family doesn't understand my sense of humor either).

Lee

Curiously, most high school and community college courses teach the negative-to-positive gospel, but college-level and beyond engineering schools tend to stick with "conventional" current flow so that they won't need to come up with new "rules" (or textbooks and syllabi). Sorta like Great Britain's resistance to switching which side of the road to drive on, or the USA's unwillingness to adopt SI (the metric system) - nobody wants to deal with the hassle of changing over, even though the benefits would be unquestionable.

http://www.allaboutcircuits.com/vol_1/chpt_1/7.html