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Discussion Starter · #1 ·
Morning all,

OK, this is a tremendously stupid question. Feel embarrassed to ask it, but it's the only way to learn I suppose.

I'm trying to get my head around batteries this morning. I think I understand the basics. Cell with plates and electrolyte, flow of ions and electrons, place a load in the path of the electrons and there's your power.

What I can't understand is how cars can be negatively grounded.

The plates react with the electrolyte, forming electrons at the negative post of the battery. These electrons are attracted to the positive post and if a circuit is connected between the two, the current of electrons will flow from negative to positive, powering whatever load might be in between.

This being the case, how is it done in our cars that current flows back to "ground" at the negative post? Surely when the electrons reach the positive post they'd prefer to recombine with the positively charged plate than go back to ground at the negative post?

Anybody got the knowledge to put an idiot out of his misery? It's driving me nuts! :)
 

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You are thinking to hard!

You are correct in that physically, electrical current in a metal conductor is caused by the flow of electrons, and that electrons flow from negative to positive.

But electricity as a phenomenon was known before the physics of electron flow in metals was understood, and electrical current was arbitrarily defined as being from positive to negative. The convention then, is that current direction is opposite from electron flow.

None of which is related to whether a car is positive earth or negative earth. It doesn't matter, the current will still go from positive to negative (and electrons from negative to positive) and things will work. All we are doing is making a decision as to which side of the circuit will be 'common' and used as the return path through the bodywork etc.

Hope this helps to stop your head hurting.
 

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Discussion Starter · #4 ·
Thanks for the reply [tony].

OK, I think I've got it straight in my head. So....

1) There's an arbitrary human concept "current" that describes a theoretical flow of electricity from positive to negative.

2) Actual electron flow will move negative to positive if a path is available.

3) The grounding of the system simply indicates that the car chassis functions as a return path to one of the battery posts: the negative post in a negatively grounded car.

So when I connect up a wire, from the negative to the positive posts with a load in between, current will flow conceptually from positive post to negative ground, electrons will actually flow from negative post to positive post but nobody minds too much because the lights work.

Is that right? :)

EDIT: Thanks for the link [yellow spider]. I've read and re-read that thing a few times, one of which was this morning -slow learner I'm afraid.
 

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Blame the historical guy who labelled the battery + and -, if he'ed have labelled them the other way round electronics and physics would be a doddle. Unlucky guess I supose.
 
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