# Thread: CREE RGBW General Questions

1. ## CREE RGBW General Questions

Hey there. I'm doing this whole lightsaber thing for the first time, and I have some simple questions regarding LED wiring. For reference, here's the LED I purchased: https://www.ledsupply.com/leds/cree-xml-rgbw-star-led

Additionally, I have a 7.4V power supply.

1) This page shows a maximum drive current of 1000mA; is that per die, or for the entire unit?

2) A question at the bottom of the page asks about using resistors to limit current, and the answer given strongly suggests using an minibuck instead - one for each color. That seems like overkill, and I'd swear I've mostly seen resistors used in this application.

3) Assuming I go with resistors, what wattage is recommended? I can figure this out myself once the other questions are answered, but I'd like the community's recommendation.

4) I've also seen some conflicting info around the internet regarding resistor sizing. From what I understand, I take my supply voltage and subtract my forward voltage, and use that value in V=IR. So the red 2.25Vf would yield the following:
7.4V - 2.25V = 5.15V
5.15V/1A = 5.15 Ohms (assuming each die is pulling 1000mA, per question 1).

Thanks for the help. I'll likely be around here a bit as I get my feet under me during my first build.

2. Welcome to the Forums. What card are you using?

3. Thank you!

4. It is 1A per die. You would be better off using the 3.7V 3400 mAh battery. We normally don’t mix any type of buck puck with sound cards, resistors are used.

5. Gotcha.

Regarding wattage, what do you recommend?

Thanks for the help.

EDIT: I went through your guide and it looks like I was on the right track (in my head) for wattage. I understand why you're suggesting the lower voltage battery, so that I don't need to compensate as much for the discrepancy with my resistors.

6. Not only that. The battery I recommended will be way more efficient for these setups. 7.4V batteries were better in the old days (CF 6 and below), but aren’t as great at driving “modern” setups. And yes, the 3.7V battery allows for way smaller resistors.

7. What amperage do you suggest running these at? 1000mA each seems like a lot of draw, and I don't know if I actually need that (from what I remember, the brightness is determined by voltage and not current, right?).

EDIT: Looked it up and saw that it's ultimately current that affects the intensity (man I'm remembering this stuff terribly). That said though, what's a good amperage for decent brightness on a saber?

8. Running them at 1A will be fine. The Reds you’ll have to check the spec sheet. They may only be 700 mA.

9. Great, thank you for the help!