What is the votage of the battery in a car? 12 V right?
Then why is Cigar-Lighter Adaptor 13.8V ?
Also, how the 13.8 (not 13.9 or 13.7) V is derived?
-- Harry
Why 13.8 V not 13.7 or 13.9?
Jun 14, 2007
25 Replies
Nominal voltage of the lead acid battery.
No it's the nominal *charge* voltage. The "at rest" voltage of a lead acid battery is nowhere near that high.
Gibbo
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OK, it is the nominal "float" voltage of a lead acid battery. Feel better?
Not especially so. Just that your first answer was wrong. Dress it up with sarcasm however you like. Doesn't alter anything.
Gibbo
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To hold a 6 cell lead acid battery at full charge, you have to apply 13.8 volts to it. The alternator is set to hold about that voltage, to charge and maintain the battery at full charge.
When it is not being charged but supplying a load (like when you turn your headlights on, but the motor is not running) then the output voltage stays near 12 volts for a significant part of the discharge time.
Charge voltage in an auto should be 14.4.
If only it was that simple.
Gibbo
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this post was made entirely with the 100% recycled electron.
The '12v' battery, has a lot of different voltages associated with it. For normal 'float' charging (in your car, with the engine running, and the battery already reasonably charged, assuming it has a modern alternator that doesn't keep trying to push too much voltage into the battery), the cells need about 2.3v/cell (13.8v). Fast charging, can use up to nearly 2.5v/cell (14.8v). Cars commonly used
14.5v, and older electrics on a car often charged all the time at this higher voltage - which is why the electrolyte needed topping up so often... Idle, without significant load, typically about 12.9v. Then during starting, down to under 7v momentarily, when 'cold cranking'. '12v', is just a figure used to distinguish this system (with 6 cells), from systems using 12 cells (lorries - nominally 24v, but up to 29v in the real world), and ones using 3 cells (some older motor bikes). It bears little real resemblance to the real figure seen in the car...Best Wishes
At what temp? (K, C, R, F) chose one, then define concentration of acid in ppm and purity of solvent, then give us a number(s).
Do I hear anything???
Have fun
Stanislaw.
One battery I had showed a label "charge voltage not to exceed 14.4V", IIRC the Optimate battery conditioner float charges at 13.6V to minimise electrolyte loss due to gassing.
But it _is_ the typical float voltage. Neither of them is "nominal" - that just means "by name", i.e., the nominal voltage of a 12V battery is 12V, even though the actual voltage is usually different from that.
As to why it's 13.8 instead of some other value is because that's the way the chemistry works out.
Hope This Helps! Rich
Re-read his original reply.
Gibbo
In accordance with our company policy of minimum environmental impact
this post was made entirely with the 100% recycled electron.
your vehicles battery is actually less than that, aprox 12 volts. The 13.8 is needed to put charge in the battery.. The alternator (Charging system) has it's own voltage regulator to maintain the 13.8 volts The voltage has been selected as the standard to use with common lead acid type batteries in this voltage range to put in a charge, but not so that it'll damage the battery.
"I\'m never wrong, once i thought i was, but was mistaken"
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12.6 fully charged, 12.0 about half discharged...
When the car is running (and charging the battery), that is the normal voltage of the electrical system.
If you tried to charge a car battery with 12V, you would get NO charge. In order to charge a battery, one must overcome the internal resistance of the battery and actually FEED electrons into it.
The 13.8 volt figure does that, and does so without too much charging current, as that must also be considered. One would not want one's battery to go BOOM!
The MeatTard strikes again.
Wrong, Slug-o!
When your IQ gets above that of a slug, come back and try again.
I don't know about that.I guess it depends who you are.
There are more than a few folk who would be pleasantly surprised if your battery went BOOM!
F*ck off, adolescent retard.
What a dreadful man!
Are you in the habit of teaching adolescents to swear? It strikes me you need a close eye keeping on you.
Are you on probation or parole of some kind?
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