Batteries and the idea of a "completed" circuit. 6

[treddie]

Howdie. It has been some years since I studied electronics (I have very little practical experience with it), but back then I had a question which seemed not to have an answer. But someone posed the same situation and now the question is back. Simply put, it is this:

Suppose you have a battery charged to 12V. If I connect a wire without a resistor across the leads, current will flow rapidly and the battery will overheat and might get destroyed, because I have completed the circuit with minimal resistance. Now if I take that same battery charged to 12V and instead of shorting across the terminals, I instead connect the negative terminal to a huge steel ground plate while leaving the positive terminal open, my sense is that no current will flow into the plate or hardly any since there is not a completed circuit. My reasoning is that the electrons in the battery are still attracted to that 12V potential inside the battery, and connecting the negative terminal to some other external ground does not attract the electrons any stronger than the potential inside the battery does. I imagine that the only possibilities are that the electrons will not get all bunched up trying to cross the battery's internal potential, and essentially "hating" each other will try to get as far from each other as the battery's design will allow. PERHAPS, a little current will flow out to the big metal plate only due to the electrons' mutual repulsion.

Is this correct, or am I getting it all wrong? Do the electrons see the huge steel plate as the other side of the battery?

Thanks for any responses!

 

[waross]

The electrons in the battery see the electrons in the huge steel plate. Due to the mutual hatred of electrons neither side (battery electrons or steel plate electrons) invade each others space.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

treddie; Don't forget that the electrons in the steel plate are totally happy where they are. They're all bound to their metal atoms. Only when an electric or magnetic field is imposed on them do they actually want to go somewhere and then only in a drift. They aren't all piled up like separated charge in a capacitor. If that were the case then there would be excess electrons and they'd probably spread out across it all. Batteries are chemical and only do anything when they are allowed to migrate thru a circuit.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[treddie]

Thank you guys, for your answers. That's pretty much what I thought. But I did forget to remember the free electrons in the metal plate. After all, that's what makes it a conductor. And those little critters in the plate hate the electrons in the battery as much as they all hate each other. "Can't we all just get along?" to coin a phrase. Apparently not! Life wouldn't exist if electrons all got along. )

Anyway...I should have bet my old boss $100.00!

Thanks again.

 

[treddie]

But I guess you meant the BOUND electrons, not just the free ones. I see how those are just as much an impediment as well to the flow of electrons until a potential forces the free ones to migrate.

 

[cranky108]

This is all good theory. But the reality is there are leakage circuits of small currents that will over time degrade the battery charge, and/or could cause rusting of the metal plate. But all this takes time, like weeks.

Just diden't know if that was important to you.

 

[VEBill]

OP: "...12V battery ... connect the negative terminal to a huge steel ground plate while leaving the positive terminal open..."

You mean (exactly) like any parked car?

"...cause rusting of the metal plate. But all this takes time, like weeks."

Weeks? See above. Seems a bit pessamistic.

 

[BrianE22]

What if the battery where changed to a capacitor? Then the negative charge of the capacitor "negative" terminal would repel the electrons in the plate creating a voltage across the top and bottom of the plate, right?

 

[cranky108]

A car is isolated from ground. Pipe on the other hand is in the ground, where it is exposed to reactive elements. There is a difference between the two.

And yes I am a pessimest a good pert of the time (it keeps me employed). Just like we don't need a military (unless we have a war). [I know this is a bad example, because I don't agree. But it is an example.]

There is a whole art to rust prevention, of which I know very little (it's the guys down the hall that know about it).
But connect a steel ground to a copper ground and you will have problems in the future. There's no power source but it happens.

 

[RyreInc]

Aren't the leakage currents internal to the battery/capacitor? I don't see how this would affect the steel plate.

The way I see it, we are talking about galvanic cells. But without an electrolyte or conductor to connect the steel plate to the positive terminal, there is no connection and thus no (accelerated) reaction.

BrianE22: no, the entire plate will be at the same potential, which is the same potential as the capacitor negative (and in this example, 12V less than the capacitor positive).

 

[treddie]

Isn't it because you can think of the steel plate and the conductor leading to it as just an extension of the battery or capacitor's negative side? The potential is still only what existed originally...between the battery/capacitor's +- barrier.

 

[cranky108]

Again, the theory works. But the reality is there is no perfect capacitor dielectric.

The question maybe over what period of time are we interested in.

So like so many times, the answer is: It depends on the details.


Never put your name on an estimate, unless you are willing to defend it as a fact.

 

[Skogsgurra]

This discussion makes me think that it is too hot for rational thinking in some places

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.