In a message dated 2/25/98 12:00:03 AM Eastern Standard Time, Bob MGT writes:
> My car runs 15V at the battery terminals with the engine running and the
> lights off. With the lights on it runs 14.5V. These were measured with an
> accurate meter. I assumed that this was too high, as I've always heard
> that 14V was the proper level. Is 15V ok? I don't want to cook my battery.
Bob,
I don't know for sure, but i wouldn't think 15 volts would be a real problem.
Most every source I've seen says the alternator output should be 14.6 volts.
For the sake of argument, let's assume the 14.6 V is chargine at a rate of 10
amps. Using ohm's law, the says the equivelent battery resistance is 14.6/10
= 1.46 ohms. With 15 volts, the charging current is 15/1.46 = 10.37 A, less
than a 3 % increase. As far as I know, the most significant factor in damage
from over charging is heat. An extra 3 % charging current shouldn't be
critical.
Keep in mind, though, that the resistance we're speaking of is not a true
resistance. It is a function of the chemical nature of the battery, and is
basically the result of "back EMF" from the battery -- EMF being
"electromotive force", what we normally call voltage. The amount of back EMF
depends on a lot of things, such as temperature, state of charge, etc. My
knowledge of such things is very limited.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition, slated for a V8 soon!
'68 MGBGT---organ donor for the '74
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