Voltage with fan on

[Ti Kan]

McCohens at aol.com writes:
> While playing with the new toy, an 80 turbo Q, I jumpered the radiator fan on 
> high speed and immediately noticed the voltage meter drop to about 12.5 which 
> seemed a little low.  At the low setting it was around 13.  Should I check 
> the fan for amp draw, alternator for output, or just drive it and enjoy.

Count yourself lucky to have as much as 12.5V! :)

Seriously, the voltmeter on the dash is only nominally useful, because
it is grounded to the same point as most other electrical accessories
(including your radiator fan).  This means that the "ground" voltage
is probably raised a small amount above 0 compared to the negative
battery terminal when there is a lot of current flowing through that
junction (due to a finite amount of contact and wiring resistance).
This causes the voltmeter to read low.  This "problem" is especially
prevalent in the older models.

If you were to take an actual multimeter to measure the voltage at
the battery terminals while the fan cycles on and off, you will see a
much smaller fluctuation.

-Ti
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