6v Batteries?

[PoorManQ45]

So, I was reading a few electronic forums pertaining to cars and I found something weird:

They said that the batteries that we use in cars that are supposedly 12V, are not really 12v. They do not have a +12V and a -12V. They really have a +6v and a -6V. Which means that the potential difference is a Total of 12v!

Is this true?

P.S. I don't remember the exact websites, so I can't link to them

[Moto Man]

Are you serious? Did somebody actually say that? They're idjits.

Car batteries are 12 volts. Actually the're a bit more than that, but everyone just rounds it down to 12.

[PoorManQ45]

Well actually, they may indeed be +6V and -6v batteries.

IIRC, they said that when you measure the voltage of the battery, you are actually measuring the maximum potential difference. So +6v to -6V would be a total of 12v.

[Moto Man]

Cars are not grounded, so it is only the relative voltage between the battery poles that is significant.

Consider if you were driving along and your car picked up a static electric charge of 1000 volts relative to the ground. So the voltage on your battery terminals (relative to the ground) is 1000 volts and 1012 volts. Does this mean you now have a 1012 volt battery? No, it is still a 12 volt battery.

People who say otherwise are being pedantic.

[Q451990]

...People who say otherwise are being pedantic.

Ohh a new word!

pe·dan·tic ( P ) Pronunciation Key (p-dntk)adj. Characterized by a narrow, often ostentatious concern for book learning and formal rules: a pedantic attention to details.

--------------------------------------------------------------------------------pe·danti·cal·ly adv. Synonyms: pedantic, academic, bookish, donnish, scholasticThese adjectives mean marked by a narrow, often tiresome focus on or display of learning and especially its trivial aspects: a pedantic writing style; an academic insistence on precision; a bookish vocabulary; donnish refinement of speech; scholastic and excessively subtle reasoning.

[PoorManQ45]

Cars are not grounded, so it is only the relative voltage between the battery poles that is significant.

Consider if you were driving along and your car picked up a static electric charge of 1000 volts relative to the ground. So the voltage on your battery terminals (relative to the ground) is 1000 volts and 1012 volts. Does this mean you now have a 1012 volt battery? No, it is still a 12 volt battery.

People who say otherwise are being pedantic.

I understand that. But what does a "12v" battery mean? Does that mean that the negative pole is -12v and the positive pole is +12v? Or does that mean that the potential difference between the poles is 12v?

[Q451990]

As far as I know all batteries are rated at the potential difference between their two poles. How would you measure the other way in any practical application?

Heath

[szh]

It is 12 Volts (or a bit more really when fully charged) between the two terminals of the car batteries. If you short the negative terminal to ground, then the potential from the other terminal to ground (the earth) is +12 Volts. If you short the positive terminal to ground, then the potential from the other terminal to ground (the earth) is -12 Volts.

There is no other way to consider it. Forget car batteries if you wish, take a D-cell battery and you will get 1.5 Volts between the two terminals and the same potential concept and logic applies.

People who are saying it is +6 Volts and -6 Volts have no clue what they are talking about ... what the heck are they doing it in reference to?

There is no such thing as absolute zero potential (for the kinds of circuits we are talking about here, of course!) - the closest thing we have to a reference is the ground (literally the Earth itself) for everything we measure.

Z
Modified by szhosain at 4:21 PM 1/6/2005