Luxeon star resistor math

[teststrips]

I want to dual voltage mod my Q3. I will baisically add a resistor to make the lower brightness setting. I've found hints in other's posts that a 10 ohm resistor would work well, but how big of a resistor is needed 1/8 watt, 1/4 watt, 1/2 watt, 1 watt, 3 watt.

I found a calculator, but don't even know what values to plug in. http://www.luxeonstar.com/resistor-calculator.php

I don't want to mess around and put something too tiny in, so if someone knows for sure what size i need, plz let me know.

 

[Doug Owen]

Like most things in life, the answer is 'it depends'.

In this case on what voltages and currents we're talking about. The power, in Watts, is the current you're running (in Amps) times the voltage (in Volts) across the resistor. This voltage is the battery voltage minus the Vf (drop on the LED for that current).

For obvious reasons, you should use a higer power rated resistor that the power you're actually developing there of course.

Let's do this the other way, what sort of battery are you going to use, what currents do you want?

Doug Owen

 

[Hallis]

jtice had a nice little piece of software on his page just for that. Might want to take a look.

Shane