RE: 13.8 Volts?/temp variations

[Ilias Glavinas <elias@tesla.wustl.edu>]

On 21 Aug 1998, Shannon Fenton wrote:

> My Voltage guage reads lower when its cool outside also? I wonder why 
> this is?


Your voltage gauge opposes the laws of nature. 

High school physics says: the battery has an internal resistance. 
Thus, if the battery can provide E volts, some of those E volts get dissipated 
in the internal resistance. So, actually, the battery is outputting:

V=E-I*r, where I is the current output by the battery and r is the 
internal resistance. 

Now, resistance is directly proportional to temperature. So, in winter, 
when your battery is at 40F or so, its internal temperature is much 
less, thus giving you a lower I*r and thus a higher V. That is why we 
see some lovely 14V or so when we start up the car in December, and close 
to 13V when starting up the car in July.

I suspect you have some strange connection somewhere in your voltage 
gauge-to-battery path.



Ilias
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