Help on choosing resistor

[reefme]

I have a LED driver rated 120W produce 103v-171v range at 700mA.
I connect 44 LEDs at 3.6v@700mA each in serie. Is 18ohms resistor correct?

Thank you for your help.

[wingedfish]

44 x 3.6 = 158.4V / .7A = 226.3ohms.


Not sure its right for you application. E over IR

[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

[toolmanbmw]

In my build I just used a 5W 1ohm resistor in series and measured the voltage drop to get the amps the driver is putting out. I am no expert.... but it worked for me anyway :)


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[reefme]

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.

[themastr]

Thats the same driver I used you should be okay with the small resistor and a 3 watt or more power rating.

they are solid drivers I've never had any issues with any of them.

thanks
erick

[reefme]

Thats the same driver I used you should be okay with the small resistor and a 3 watt or more power rating.

they are solid drivers I've never had any issues with any of them.

thanks
erick

Do you mean small resistor = high value of resistor?

[beefORchicken]

you don't need resistors because the driver supplies a regulated current of 700mA regardless of what the load is, as well LEDs are still diodes and they will maintain their 3.6V across them regardless of supply voltage. the extra voltage will be dropped by the driver
resistors can be used as drivers but are only a good choice for low power situations (indicator lights etc.)

[themastr]

Sorry I didn't explain myself better.

I meant that you can put the 5ohm resistor with a 3 watt rating in series on your string to see the amount of current you have. all you will have to do is test the voltage across the resistor and then use this formula to find your current.

I = E/R so the voltage drop across the resistor divide by the resistor value.

BeeforChicken is correct you don't need to add any resistors. What was your purpose to adding the resistor in the first place. I asked that in the earlier post? I don't think you answered it or did I miss it?

I used one because I was troubleshooting and also wanted to know how much current was going pass my LEDs. If you're just building and never will tamper with it just hook everything up without the resistor. Everything should work fine.

hope this helps

thanks
Erick

[reefme]

Sorry I didn't explain myself better.

I meant that you can put the 5ohm resistor with a 3 watt rating in series on your string to see the amount of current you have. all you will have to do is test the voltage across the resistor and then use this formula to find your current.

I = E/R so the voltage drop across the resistor divide by the resistor value.

BeeforChicken is correct you don't need to add any resistors. What was your purpose to adding the resistor in the first place. I asked that in the earlier post? I don't think you answered it or did I miss it?

I used one because I was troubleshooting and also wanted to know how much current was going pass my LEDs. If you're just building and never will tamper with it just hook everything up without the resistor. Everything should work fine.

hope this helps

thanks
Erick

Thank you so much. I asked the question, because one of my blue LEDs burned out.