Wiring & Resistor Check Please

[darth_chasm]

Hi,

Hoping folks could check out my wiring and resistor set up to confirm or advise. I think I got it, but it's a new area for me so any help is appreciated.

Here are the details.

NB V2 Board w/Power Extender

18650 3.7 3400mA PCB Battery

Red/Red/White Cree XP-E2 CopperNova
Red Vf 2.59V @1000mA (x2)
White Vf 3.15V @1000mA

2.1MM Recharge Port

Mom Tactile Switch 17

Resistor Calculation:
Red ? (3.7V - 2.59V)/1A = 1.11Ω | 1.11Ω * 1^2 = 1.11W (1.2Ω 1W resistor needed)
White ? Bypassing 2520 SMD (3.7V ? 3.15V)/1A = 0.55Ω | 0.55Ω * 1^2 = 0.55W (1Ω 1/2W resistor needed)

[Bark]

Question to the gallery: Do we run Red Cree XP-E2's at 1A? (I guess I'm used to running the Rebels at 700mA.)

I recommend that you give each LED it's own dedicated resistor. You currently only have one for both reds. Theoretically, there's no problem. However in reality, if one die draws a little more current than the other, it will eventually pop. The surviving die will then take the surplus current and pop too.

[Silver Serpent]

Bark is correct. It is generally safer to use a resistor on each die. If you decide against this advice and still want to use a single resistor, the current required will be 2A (1A for each die wired in parallel). You've only plugged in 1A in your calculation.

Yes, the Cree Reds can be run at 1A with no issues.

Wiring diagram looks fine.

[darth_chasm]

Ok, makes sense. I noticed I also missed rounding up for the wattage.

New Resistor Calculation:
Red - (3.7V - 2.59V)/2A = .56Ω | .56Ω * 2^2 = 2.24W (1Ω 3W (x2) resistor needed)
White - Bypassing 2520 SMD (3.7V - 3.15V)/1A = 0.55Ω | 0.55Ω * 1^2 = 0.55W (1Ω 1W resistor needed)

So would the new wiring look like this?

[Silver Serpent]

I think you misread my instructions. If you wanted to use one resistor for both reds (not ideal), then you'd calculate at 2A.

If you're using a resistor on each red individually (better solution), then you'll keep the current at 1A.

The updated wiring diagram is correct. Remember to bridge the two + pads on the PEX, or just join that red and yellow wire together. Either way works.

[darth_chasm]

Ah I see. I think I'm on my way now.

Thanks so much to the both of you for the guidance.

[Bark]

@darth_chasm: The figures that I come up with are the following -
Red = 1.11 Ohm, 1.11 Watt --> 1.2ohm, 3w resistor (Brown-Red-Gold) x 2 (on each die individually)
White = 0.55 Ohm, 0.55 Watt --> 1ohm, 2w resistor (Brown-Black-Gold)

My pleasure to help. I actually might just steal your revised wiring diagram for my latest project, so it will even out.


@Silver Serpent re:1A for reds - Thanks for the confirmation. I had already bought the parts and was pleasantly surprised to see that at a previous point in time, I knew the 1A piece of information because the resistors I had bought were correct for 1A. With each passing day the memory gets worse, but at least I don't have to buy new resistors.

[darth_chasm]

Absolutely, feel free to. Let me know if you want an eps version to edit.