PWM Fan - can it run directly off 3.3v, 5v or 12v inputs/GND?

[Trash80toHP_Mini]

I've got a case with 3 PWM fans and an incompatible (Beige G3) logic board. I'd like two fans to run off a power level a step below the third in any combination of the three voltages available on an ITX PSU.

Does this amount to a simple hotwire kluge or do they need a controller to function?

 

[luRaichu]

Does this amount to a simple hotwire kluge

Yes. Just hook up the red wire to your voltage and the black wire to ground

 

[Byrd]

... they will work fine but full RPM, so check the specs Trash80 that you're not buying a wind turbine

 

[Trash80toHP_Mini]

... they will work fine but full RPM

Assuming they're 12v max fans per PWM spec, they won't be full RPM @5v or 3.3v, no?

so check the specs Trash80 that you're not buying a wind turbine

I imagine I could build a hovercraft with a IIsi using these things. They were set up blow straight into this 2U server case thru a full frontal dust filter. I have them blowing out the backside, still sucking air in thru a different full frontal dust filter.



Ductwork will direct air straight thru the heatsink at 5v driven RPM, the other two are 3.3v RPM gravy I think.

 

[Byrd]

A 12V fan at 5V might not spin up, need to check specs of unit

 

[Trash80toHP_Mini]

Might it be as simple as adding resistors to limit the voltage reaching the fans from a 12v feed?
I'd imagine that a control board with rheostats might suffice for a controller?

 

[ymk]

If you need speed control, get a PWM controller.

If you just want to slow them down, fans can be grounded to 3.3V or 5V.

 

[Trash80toHP_Mini]

If you need speed control, get a PWM controller.

No need for that.

If you just want to slow them down, fans can be grounded to 3.3V or 5V.

That's exactly what I was thinking in my original post.

I have to use an ATX 24pin to 20pin adapter cable for the BG3 and I've got some short 24M-24F cables. The unused pins are 3.3v, 5v,12v and GND. To figure this out, I'm just gonna lop those wire off the 24 pin source ahead or the 24pin to 20pin adapter cable and fiddle with it.