Help on choosing resistor

[reefme]

Originally Posted by themastr

If your driver is auto ranging you would not need to put in a resistor in series? you said that its ranges from 103v-171v DC. So 44 LEDs X 3.6V = 158.4 v. you're within the range. Now if you are looking to put a resistor in series so you can check the voltage drop and then calculate the current across your string then I think it would be 12.6v/0.7a = 18 ohms

P=IE so you will need to get a P=0.7x12.6 = 8.82 watts minimum rating on the 18 ohms resistor.

someone please Double check this work its been a long time since I built my Led build.

you can also put just a smaller resistor in series so it acts like a single led.

R=E/I = 3.6v/0.7 = 5.14 ohms or a greater resistor and the wattage should be
P=IE= 0.7a X 3.6v = 2.52 watts

I think I used the smaller resistor for mine less heat and doesn't max out the driver output.

hope this helped a bit

But please someone recheck the work. it's been awhile ;D

thanks
erick

i am using a Inventronics:120W produce 103v-171v range at 700mA.