Resistor calculation math?

[Noyl Wendor]

Howdy,
I'm setting up a Tri-cree GGW (white FOC) with a nano 2.0.
I came up with a 1.2ohm 3watt resistor.
3.58-3.7 = .12 /? . mA? or round up to 1A? my resistor is waaaay to big, I see green but both dice are really dim. Same as the guy trying to figure out his wrong turn

[Generic Jedi]

Resitor = (BatteryVoltage - LEDforwardVoltage) / Current (measured in amps). Your battery is 3.7 volts. The forward voltage for the green LED is 3.58 volts, and the white is 3.15 volts. You can run the Cree LEDs at 1 Amp.

Power (watts) = (BatteryVoltage - LEDforwardVoltage) x Current.

You'll want to put resistors on each green.

[Greenie]

I've also used a GGW Cree, White FOC I used a 0.47ohm 1w just for safety's sake. The greens in parallel sharing a 0.5ohm 3w. Saber works just fine and they are almost brighter than the sun

[Generic Jedi]

What's the equation for one resistor on two die in parallel? Isn't it safer to use one resistor for each LED?

[Noyl Wendor]

I figured my calculation at 1amp. that's were I ended up with the 1.2ohm resistor. I didn't figure I would have to resistor each green, they are in parallel. so the one resistor on the "+" should do the trick for both. I'm just wondering if I'm horribly wrong somewhere else now

[Greenie]

With greens in parallel at 1000mA each you need to calculate at 2amps
Yes, everyone will say resistor on each die is best practice but I've watched Madcow's vid for wiring a nano with pex and he 'showed us' two dies in parallel with one resistor and let's be honest he is an expert saber smith and it is tutorial for those who want to know how to do it.
If it works for Rob then it works for me

[Noyl Wendor]

With greens in parallel at 1000mA each you need to calculate at 2amps
Yes, everyone will say resistor on each die is best practice but I've watched Madcow's vid for wiring a nano with pex and he 'showed us' two dies in parallel with one resistor and let's be honest he is an expert saber smith and it is tutorial for those who want to know how to do it.
If it works for Rob then it works for me

Yep I watched the same vid. So I'm really sure its my math for the resistor. Or there's a hiccup I'm not seeing

[Forgetful Jedi Knight]

What's the equation for one resistor on two die in parallel? Isn't it safer to use one resistor for each LED?

It is safer to use one for each die, and that is how I teach it. And the tutorial that I wrote is in the LED Wiring Section.

[Forgetful Jedi Knight]

Resitor = (BatteryVoltage - LEDforwardVoltage) / Current (measured in amps). Your battery is 3.7 volts. The forward voltage for the green LED is 3.58 volts, and the white is 3.15 volts. You can run the Cree LEDs at 1 Amp.

Power (watts) = (BatteryVoltage - LEDforwardVoltage) x Current.

You'll want to put resistors on each green.

Not quite accurate, you might want to check out my tutorial for the proper "power" calculations.

[Bark]

It is safer to use one for each die, and that is how I teach it. And the tutorial that I wrote is in the LED Wiring Section.

We have said this elsewhere: if one die pops, the other one is GUARANTEED to pop too if you combine into one resistor. A die popping is more likely too, as a manufacturing defect/imperfection could cause it to draw more current than designed, and you would be happily giving it twice the current it's designed to take.

Resistors are cheap. Wiring one for each isn't that bad. The question is whether the risk is worth the reward. The reward is that you'll save yourself five minutes, a couple of cents, and a little room. The risk is that you'll have to remake your entire LED module later.