I am getting an odd reading from an array of LEDs, which I could do with a little help understanding. I have a very specific project, but to abstract this question from that, let’s assume the following:
I have 24 LEDs in 4 sets, each of 6 LEDs with a 68ohm resistor. They are 1.8v LEDs using 20mA and I have a 12v supply.
I understand how to calculate the required resistor and current for single LEDs but I used the rather excellent http://led.linear1.org/led.wiz to do the math for me on this. It concludes my array will use 80mA.
However, when I use my meter, it tells me the array is only using 8mA?!
I am planning to run this from my Arduino Micro, which can easily deliver 8mA from a pin but certainly not 80mA, so the difference is crucial to me.
Initially I thought I was reading the meter wrong (it’s new) and I was out by a factor of 10 but the only other thing of a known(ish) current I could benchmark my meter with at 12v was the Arduino itself, which is drawing 37mA, which to me sounds about right (and 370mA would seem too high for a Micro), meaning my meter is probably correct?
I know you can get variations in LEDs or whatever, but I have 3 of these arrays and they are all reading the same ~8mA. What am I missing or should this array be pulling only 8mA? How should a parallel array of in-series LEDs be calculated?
Thanks for any help.