My source voltage is 12 volts. LED forward voltage is 3 volts and the forward current is 20 mA. I can do the math to get the resistor values and the wattage values for the resistors. However I try, I do not know how to find the current that the array draws. I have tried Ohm's law and Watt's but I just can not come up with the array drawing 100mA from the source. Would be thankful for any and all help. This information was put into the LED.linear1.org website.

 

hi Kevin,
Welcome to AAC,
Each string draws 20mA and there are 5 strings, so 5 *20mA =100mA
Is this what you are asking.?
E

Update:
3 * 3Volt LED's = 9V drop across the LED's , leaving a 3V drop across the 150R. I= 3V/150R = 20mA.

1 * 3Volt LED's = 3V drop across the LED's , leaving a 9V drop across the 470R. I= 9V/470R = ~20mA.

 

Thanks so much Eric. I don't know how I could be so silly. It has been a long time since I have sat down and worked the math on a circuit.