Tamariniak OP t1_ja30ptt wrote on February 26, 2023 at 1:51 PM

Reply to comment by idk_01 in Best way to run PC fans from outlet? by Tamariniak

What about the voltage and current ratings though? What does it mean when a fan says "12V/0.3A"? Is that the maximum, the minimum, or something else? It makes me a bit scared to use lower voltages.

I also saw people saying that the fan "will always draw 0.3A regardless of the voltage," but I find that a bit weird. Surely a 12V/0.3A rating would mean that the fan has a resistance of 40 Ohms and the current would just be I = V / R.

SomethingIrreverent t1_ja3cq3n wrote on February 26, 2023 at 3:24 PM

You need a 12V adapter that can supply at least 0.3 A. If you have a 12 VDC adapter that can supply more current than that, it will work fine. If your adapter can only handle 0.2 A, you'll have trouble.

5degreenegativerake t1_ja3fy5q wrote on February 26, 2023 at 3:46 PM

And if you have “a couple” fans, you need 0.3A per fan on the wall wart spec.

Diligent_Nature t1_ja3vqbp wrote on February 26, 2023 at 5:31 PM

>people saying that the fan "will always draw 0.3A regardless of the voltage,"

That's nonsense. 0.3A is the nominal current. Lower voltage=lower current. It could be a little higher if airflow is impeded.

>Surely a 12V/0.3A rating would mean that the fan has a resistance of 40 Ohms and the current would just be I = V / R.

Ohm's law applies to DC in resistors. Fans use coils which have inductance as well as resistance. They commutate the DC into AC for the coils. Plus most DC fans are brushless and you can't measure the resistance directly because of their electronic commutation.

discotim t1_ja4ae0o wrote on February 26, 2023 at 7:06 PM

You want 12 volts and go overboard on the current, 2 Amp or more wall or inline warts are tiny. The fans will only draw the current they need and won't tax the power supply.

kyrsjo t1_ja58joo wrote on February 26, 2023 at 10:58 PM

You don't want to go too far overboard tough, switch mode power supplies aren't really stable without load.

idk_01 t1_ja5imz7 wrote on February 27, 2023 at 12:10 AM

12V/0.3A means that it requires 12V and .03A

The fan manufacturer has a datasheet out there somewhere that will have the tolerances of the device (i.e max & min levels etc.)

But for practical usage any 12v source, be it a battery or an ac/dc adaptor, that can supply at least .3 Amps should power your fan.