Re: Amps drawn

["Graydon D. Stuckey" <graydon@apollo.gmi.edu>]

On Wed, 5 Jun 1996, Robert Houk - SMCC Bos Desktop Hardware wrote:

>    > =09So, if you have 55w driving lights, and your battery puts out=20
>    > 12v, the conformulation would be:  110w / 12v =3D 9.17amps.
> 
>    I have found from actual current measurements that the wattage ratings=20
>    are not very accurate, so you would be best to use a good Fluke (or=20
>    similar meter) and actually measure the voltage and the current, to=20
>    determine the wattage.
> 
>    The above formula also illustrates why relays work so well.  They get you=
>    =20
>    more volts at the light, which reduces the current.  The higher voltage=20
> 
> ***WRONG***

Well, OK, I have to state that given the wattage as a constant, then the 
above would be true.  An error, yes, but a full blown "***WRONG***" ?  I 
guess that isn't as bad as a "Bbbzzzzzzzzztttttt!"  :-)

> Current is directly proportional to voltage (if voltage goes up 10%, then
> the current flow will go up 10%), and the power dissipated goes up as the
> square of the voltage (or the current) change accordingly.

I thought that P=VI, (power = voltage * current)

and power = (Current)^2 * Resistance

>From P=VI, that means that power is proportional to voltage and also 
proportional to current.  Keeping power constant, if you increase 
voltage, then current has to go down.  I suppose it is possible that with 
higher voltage at the bulbs, that the power rating of the bulb goes up a 
little, which would allow a little more current.

> Relays work so well because you're bypassing all the shitty (sorry, but
> it's the truth) Audi Factory wiring with [presumably] high-guage direct-
> wiring with only the relay between the load (lights) and the generator
> (alternator, battery), and using a good [presumably] high-current relay,
> so that overall the resistance of the wiring is much less, therefore

That's what I was thinkin' too.

Later,								
Graydon D. Stuckey								
graydon@apollo.gmi.edu								
Flint, Michigan   USA
'86 Audi 5000 CS Turbo Quattro, GDS Racing Stage II