Super basic noob question

[Legume]

I'd just like to check my work before actually jumping in on anything, so thank you for your time looking this over!

I'm getting the pre-assembled RED led module (http://www.thecustomsabershop.com/Cr...dule-P998.aspx) can I use the 3.7V 18650 Li-Ion instead of the 7.4V? I'm waffling between the 3200mAh Panasonic (http://www.thecustomsabershop.com/Pa...ery-P1282.aspx) and 2600mAh (http://www.thecustomsabershop.com/Li...dule-P672.aspx) since I was planning on getting two so one can be charging while using the other. How significant is the difference in battery life going to be realistically?

For the resistor I did the math. (maybe, hopefully, correctly even)

The Math:
Assuming this (http://www.thecustomsabershop.com/Re...ova-P1001.aspx) is the led that's in the module...
Cree Part# XPEBRD-L1-0000-00801
73.9 Minimum Luminous Flux @ 350mA
Forward Voltage @1000mA = 2.65v

R <Ohms> = (3.7 - (2.65)) / 1A
R = 1.05

P <Watts> = 1.05 * 1A
P = 1.05

1.05 ohm, 1.05 watt resistor?

Would it be better to go with the

• 2ohm 1w (http://www.thecustomsabershop.com/2o...?ItemId=427565)
• 1.2ohm 3w (http://www.thecustomsabershop.com/12...?ItemId=427566)
• Something else...?

Thank you very much!

[TheUnchosenOne]

You should get the 3.7V one, the 7.4 will require a pretty big resistor and you don't really need it.

The difference in run-time will be roughly 30 minutes, but with a single LED you're still going to get something like an hour and 45 minutes with the 2600, and a bit over 2 with the 3200.

Your math is right, but just keep in mind that the forward voltage on the data sheet is very probably not correct, and if you can measure it on the LED itself you should.

When getting resistors, you want as close to the calculated values without going under. You have a little more leeway with the wattage, as it doesn't really matter how high it is, other than the fact that higher wattages mean bigger resistors. The ohm you do want close, so the 1.2ohm 3w resistor is probably the one you want.

[Legume]

Thank you! That was really helpful and I've got my order put in now.