Correct Resistors? Ohm's Law Understanding Check

[ColdVizjerei]

For my first build, I blindly followed diagrams found on these forums and managed to get a fully functional lightsaber!
However, I want to know what's going on so I've been reading up on Ohm's law and was wondering if my understanding is correct.

The scenario is, I have a Red/RoyalBlue/White Tri-Cree and want to mix the red and royal blue for a pinkish blade. With a NB, PeX, and 3.7v battery, the resistors are as follows:

Red- 2.59v run 1000mA
R = (3.7-2.59) / 1 = 1.11 which rounds up to 2
p = (1.11)*1^2 = 1.11 which rounds up to 2
Thus for the red die, I'd need a 2ohm 2W resistor

RoyalBlue- 3.41v run 1000mA
R = (3.7 - 3.41) / 1 = .29 which rounds up to 1
p = (.29)*1^2 = .29 which rounds up to 1
Thus for the royal blue die, I'd need a 1Ohm 1W resistor

White- 3.15v run 1000mA
R = (3.7-3.15) / 1 = 0.55 which rounds up to 1
p = (0.55)*1^2 = 0.55 which rounds up to 1
Thus for the resistor on the white, I'd need a 1Ohm 1W

Is my understanding correct?

[Silver Serpent]

Your math is fine, but you're rounding up an unnecessarily large amount for the Ohms. The Red can use the 1.2 Ohm 3 watt in the store: http://www.thecustomsabershop.com/12...istor-P22.aspx

The Royal Blue and the White can use the 0.5 Ohm 3 watt: http://www.thecustomsabershop.com/5o...tor-P1050.aspx The White will be just fine as the FoC.

[ColdVizjerei]

Oh wow, I didn't realize that the store carried those resistors!

Additional question: since I'm unnecessarily rounding up for the Ohms, how come the watts for the resistors you suggested are so much higher?

[Bark]

It's what's in stock here.

Rounding up is good for safety. Only rounding up the minimum amount is good for show, for the Ohms. For the wattage, it's just a space issue. For your resistors, the space issues aren't that significant, relatively speaking.

[ColdVizjerei]

got it!
So if I wanted to make a more blue-ish purple blade as opposed to pink, I'd have to increase the Ohms on the resistor for the red die?

[Silver Serpent]

That's correct.

[ColdVizjerei]

sweet, thank you everyone for the replies!

[ColdVizjerei]

Just realized that while trying to get the desired shade of purple for my first saber, I used two 1ohm2watts resistors, one after the other, for the red die.
Is this a bad practice? I didn't have any higher ohm resistors on me at that time so I figured this would be the next best way, but are there any adverse effects of doing something like that?

[Taki117]

Other than it being more inflexible because you have 2 not bendy bits together, there's nothing electrically wrong with having two resistors in series to get a higher ohm equivalency. As long as they are on the same side of your circuit they are fine.

[Silver Serpent]

Yeah, that's perfectly acceptable. It just takes up more room.