Tamariniak OP t1_ja3izr0 wrote on February 26, 2023 at 4:07 PM

Reply to comment by Old_Geek in Best way to run PC fans from outlet? by Tamariniak

So please let me know if I'm understanding this right:

The stated voltage (12V in my example) is the maximum voltage
The stated current (0.3A in my example) is the maximum current
The current going through the fan can be calculated using Ohm's law, I = V / R, where R = Vmax / Imax (40 ohm in my example)
I just need to make sure the sum of the currents going through each of my fans is less than what the PSU is rated for

I saw some people elsewhere suggest that the current flowing through the fan is constant and not dependent on the supplied voltage, but that doesn't really make sense in my head since I don't think the fans could just magically reduce their resistance.

aldol941 t1_ja3u4zg wrote on February 26, 2023 at 5:21 PM

The equation I = V/R shows that current is proportional to voltage.

Applying more than 12V to the fan will force more current thru the fan and could melt the tiny wires in the fan motor (or at least shorten its life span).

You are correct, do not try to draw more current from the PSU than it is rated for. Using a PSU that has much higher current capacity is OK.

Dysan27 t1_ja7evqe wrote on February 27, 2023 at 12:03 PM

Yup.

Couple of additional things to take note of. You do not have to run the fans at 12 volts, if you run them at lesser voltage they will spin slower, an thus be quieter (if that's important to you). Though there is usually a minimum voltage that they will not operate under.

You will also see talk about 3-pin and 4-pin fans. Don't worry about it. For your use case, ie running it of a separate power supply, it makes no difference. The 4th pin is use for PWM (pulse width modulation) which is a different way to modulate the fan speed. If you're not using it 3 and 4 pin fans operate exactly the same way.