Alternate Resistor...?

[Cire Yeldarb]

Hi guys,

So I decided to go with a Nano Biscotte rather than a Petit Crouton to run the Red-Orange Rebel Star I am going to get, which means I need a resistor now. I used a Resistor calculator to make sure I was getting the right results and I came up with needing a 2.2 OHM, 2 Watt Resistor... (3.7 Source Voltage, 2.3 Forward Voltage, and 700mA Forward Current)

I can't find one of these resistors in the store, I see a "2.2ohm 5w resistor" or a "1ohm 2w resistor" (each has a different half of what it said I needed)...

Would either of those (or a different resistor) work? I don't know whether the OHMs, Watts, or both are equally important when it comes to driving the LED?

Thank you!

[Silver Serpent]

Go with the 2.2 Ohm, 5w resistor. Wattage is a minimum, you can always use a larger value. Don't go overboard, since the higher wattage resistors are physically larger and eat up precious room inside your hilt.

Try to keep your ohm value as close to the calculated value as possible.

[Cire Yeldarb]

Thank you so much again! You've been extremely helpful as I've tried to sort out my next Saber's wiring! You'll probably see one more "wiring diagram check" post from me after I get a chance to re-do it for the NB rather than the PC

[GFJedi]

You may also want to try your local RadioShack for the resistor you need, if size of the 5w resistor becomes a concern.

Also, you do not need to drive the led at exactly 700mA, you can get away with a little wiggle room overdriving the red/orange/amber over 700mA, and can go as low as 350mA at the cost of extra brightness, but benefit of extra battery life.

[oliver83]

@Cire Yeldarb, The wattage of a resistor just determines the maximum amount of current that will be flowing through the resistor at any time. Basically a 2W resistor at 2.3V will allow less that 1A to flow through it and will get damaged if a current surge of higher values goes through. A 2.2ohm and 5W resistor is the correct choice for you considering your limitations. We have a general rule to actually order double wattage resistors and capacitors just to be on the safe side. Even if your nominal current value through a path is 0.7A, there is a chance that there can be a current surge at the ver bigening with a current value much larger than 0.7A which could be catered by a 5W resistor, not a 2W one.

[Cire Yeldarb]

Hmm, fascinating. Thanks Oliver!