Why 13.8 V not 13.7 or 13.9?

Jun 14, 2007 25 Replies
M

Right, but it's not that simple. They are called 12 volt batteries because they have 6 cells that operate at close to 2 volts each for to explain the 12 volt nomenclature used. Are they exactly 12 volts - no. The chemistry used determines the voltage seen, and the chemistry used changes slightly as the years go by. The trend is upwards in the last 30 years but only by a few tenths of a volt.

I have no clue as to which or what Cigar-Lighter Adaptor you are referencing. In general terms though, the 13.8 volt level would be referring to the engine running, battery charging voltage levels which vary quite a bit depending mainly on alternator temperature, from

14.75 to 13.3 volts. It is supposed to vary according to battery temperature but doesn't just for an example of the not so perfect real world.

Your questions deal mainly with semantics and absorbed double talk, don't get your feet fouled up in that stuff as it's pretty nasty stuff to normally be avoided.

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J

You, and your assessments are nearly as retarded as the idiot I was beating down.

Take a hike, twit. (You gave yourself away, sock puppet, with your retarded follow up).

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B

2.25 to 2.3 Volts per cell at 25°C
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Boris Mohar
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J

no. it's only called a 12V battery

itr's connected to the battery.

typical voltages range from 13.5 to 14.4,

but sometimes (rare events) it'll be less than 10V or more than 40.

Bye. Jasen
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M

Less than 10V can happen when you try to start the engine. It isn't that rare.

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A

snipped-for-privacy@my-deja.com wrote: In general terms though, the 13.8 volt level would be

Andy comments: mel's advice above is accurate, from my experience.

I keep a digital voltmeter on my car battery so I can see what the charging system is doing. In the winter, the terminal voltage at the battery, when just starting out, is about 14.5 volts. On a hot summer day, after everything heats up, it is about 13.5 volts. The temp compensation in the alternator is supposed to track the battery terminal voltage, which changes in temp. Naturally, the alternator and battery never track perfectly, but it's a lot better than putting a hard 14.5 volts on the battery, as the charging rate would vary all over hell....

When the car has been setting overnite, and the space charge around the internal plates has disappeared, the battery voltage is 12.5-12.8 volts, or so, when the key is turned on and before the starter is engaged. As soon as the engine fires, the alternator raises this voltage to the charging level, above.

Having a readout of the battery voltage has saved me from several breakdowns over the years as I could spot changes in the system performance which let me know the alternator had a problem ( bad diode, etc) long before the battery would go dead while out on the road...

Just my observations from many years of driving in summer and winter, and watching the battery voltage.....

Andy W4OAH

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