Buying A Computer “Case” Fan… Does It Always Run At 100% Unless Told Otherwise?

Question

What happens if I do not plug it into the motherboard and it does not have a switch?

I have seen fans before with an "off/low/high" switch that allows you to manually set their speed.

I have seen fans that plug into the motherboard and are controlled by the OS.

I am curious... what does a fan do by default when plugged into a PSU? Does it run at 100% unless otherwise told to go slower? This is what I would expect...

Answer 1

Well, kind of. Fan speed control is done by varying voltage. If you're plugged into a motherboard, that's what it does. If it has 3 wires, the third wire tells the motherboard what's the speed the fan is running as.

Else, assuming the power source is unaware its a fan, and is at a fixed voltage, yes, it goes are full speed all the time

Answer 2

Like the other guys said, pretty much yes, but I can think of 3 exceptions:

1. A few fans have a built in thermistor that will adjust speed depending on temperature.

2. PSU's with specially marked Fan-Only PSU connectors (Antec TruePower 550W) can adjust the speed of the fan:

   

3. If you plug it into the PSU molex using the 12/5 volt rails (7 volt) or 12/7 rails (5 volt) it'll be run slower, but at this point you're modding.

Answer 3

That's pretty much it - if the fan just has a power connector for one of the plugs on the PSU it will run at full speed all the time unless you fit a controller unit.

Full speed ahead!