Hi, everyone ,what ohm to resistor can i use for

Batt = 3.7 v
Ir led = 30 ma , 1.3 v x 12 pieces

 

Hello,

You can make 6 strings of 2 leds, as the leds are 1.3 Volts.
The needed resistor will be:
R = ( Vbattery - 2 X Vled ) / LEDcurrent = ( 3.7 - 2 X 1.3 ) / 0.03 = 1.1 / 0.03 = 36 Ohms.
The closest E12 resistor value is 39 Ohms.

Bertus

 

Thank you

 

And note that each string of two LEDs needs its own 39 Ω resistor.

You LED current will vary quite a bit as the battery voltage drops, which may or may not be an issue.

Your total draw is going to be in the 150 mA to 200 mA range, which may or many not be an issue as far as battery capability/capacity is concerned.

 

Thank you