I have a pump (6-12V 4-5W) that i want to power up with a generator (9V 1.5A).
I've calculate the current needed with : I = 5W/8V = 0.55A. Next i've calculated the resistance needed : R = 9V / 0.55A = 16 Ohm Finally i've take a 22 Ohm resistor that i plugged in serial.
Despite all of this the pump doesn't work.. But if i just power up the pump directly to the generator without a resistor it works. Could you explain me why my method with the resistance doesn't work, and why it works without it ? Thanks!