What size potentiometer do I need to turn 500mA to 20mA?

Question

10K? 20K? 100ohm? What does the size of the potentiometer stand for/mean?

Answer 1

It depends on the resistance of the load. For example, it you have a load of 100 ohms and 500mA are going through it, then to get 20mA going through it


V= IR
V = 0.5 * 100 = 50V

R = V/I
R = 50/0.02
R = 2500 ohms
But you already have 100 load, so you need 2400 ohm potentiometer (round up to the next value, say 5000 ohm)

Note small pots have a power rating of about 1/2 watt. This pot needs a power rating of (P=I^2 R) = 0.96 watts