Electrical schoolwork...

[Ti Kan]

This depends on the actual value of the resistor chosen, and the voltage
"seen" across the resistor.  Let's say if I was willing to live with a
slightly dimmer LED output and chose to run 10mA through the LED rather than
20mA as in my original post, then the resistor would need to be

	(13V - 3V) / 0.01A = 1K ohms

And the power dissipation in that resistor would then be:

	(13V - 3V) * 0.01A = 0.1W

As you can see, a 1/4 W resistor would have sufficed in this case,
but I would probably stil be more comfortable with a 1/2W resistor.
I like to over-engineer things a bit to ensure plenty of safety margin.

-Ti
2003 A4 1.8T multitronic
2001 S4 biturbo 6-sp
1984 5000S turbo
1980 4000 2.0 5-sp
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Kurt Deschler writes:
> Most of the panel mount LEDS use 1/4W resistors and seem to hold up fine.
> 
> 	-Kurt
> 
> > When selecting the resistor, be sure that its rated power is high enough
> > given the voltage and current.  The formula is:
> >
> > 	P = V * I
> >
> > Or 10V * 0.02A = 0.2W.  You should use a resistor at least double (if
> > not higher) that wattage to ensure that it won't burn up.  In this case,
> > a 0.5 resistor is marginally ok, but I would feel better with a 1W
> > resistor.
> >
> > -Ti