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# I have a PCB BOARD set up for 150x 5mm IR LED's would Fifty 1/2w 56 ohm resister work? Answered

Infrared spotlight project.

I have a PCB BOARD set up for 150x 5mm IR LED 1.5-1.6 forward voltage. Forward current is 60 mA

150 LED’s are divided into 50 groups (3 LEDs each + 1 resistor)

What ohm resistors are needed for the 50 groups of three LEDs each? I was thinking of using x2 18350 Ultrafire 3.7v x2= 7.4 volts.

Suggestions on more or less voltage using increments of 3.7.

Infrared spotlight project.

I have a PCB BOARD set up for 150x 5mm IR LED
1.5-1.6 forward voltage.
Forward current is 60 mA

150 LED’s are divided into 50 groups (3 LEDs each + 1 resistor)

What ohm resistors are needed for the 50 groups of three LEDs each?
I was thinking of using x2 18350 Ultrafire 3.7v x2= 7.4 volts.

Using the online resistor led calculator. For 150 LEDs grouped 3 LEDs + 1 resister
The answer given was x50 1/2w 56ohm resister needed.
Being a broke novice I don't want to order and wait for fifty wrong resisters.
Do you think this is a safe bet? To better understand my confusion please refer to item #251216249922 on eBay or look up pcb board for 150 x led 3mm or 5mm.
The third photo completed tells a lot. Thanks again for the help!

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## Discussions

Are you sure, the LEDs have a forward current of 60mA at 1.6V?

Anyway, let's do the math:

Voltage at resistor: Ur = Uin - 3*Uled = 7.4V - 3*1.6V = 7.4V - 4.8V =  2.6V
The current through the resistor is 60mA, same as the diodes.
So, the resistor is R = U/I = 2.6V / 0.06A = 43.333Ohm
There aren't 43.333 resistors, but you can get 47Ohm resistors.

The power on the resistor is P = U*I = 2.6V * 0.06A = 0.156W
Yep, 0.5W resistors will be fine.

On the other hand, the whole assembly will produce 50 * 0.156W = 7.8W plus the loss from the LEDs.
As the total current will be 50*0.06A = 3A, the total power consumption will be 3A*7.4V = 22.2W. As most of it will be heat supply some good cooling.

You will receive 150 pcs 5mm Infrared LEDs.

Features:

Emitted Colour : Infrared

Size: 5mm

Lens Color : Water Clear

Forward Voltage (V) : 1.5~1.6

Forward Current (mA): 60mA Continuous, 120mA peak for 10% Pulse Width

wavelength (nm):850

View Angle: 15-30 degree.

I could go with one ultrafire 3.7v battery if it helps!
Did you have a look at the photo on eBay?
The board holds 150 LEDs . And has a resistor beside every three LEDs
The ends look odd? One row on far left and two on far right.
Are you saying that 1/2w 56ohm is wrong? I'm simple? What will work?
Above is a cut and paste on the led specs.
Help!,, thanks

I wish I could copy the photo off eBay it would show my dilemma it's how the board is set up to accept one resister for every three LEDs . I think the wright resisters would be 1/2 w 56 ohms. Can anyone check my work?
Thanks so much.