Undervolting fans

[NeXT]

For a while now I've been taking higher voltage fans (DC brushless) with high CFM and undervolting them so that they have close to the same CFM as the original fan but are far quieter. For example replacing a 12v 80mm fan with a 24v version. Doesn't provide as much of a breeze but still drafts air through a 486 box.
Someone said I shouldn't do that because they draw more amps and it can burn the motor driver out. I have not done prolonged testing but does sound like a thing?

 

[Chuck(G)]

Nah, I've got a couple of setups here using 24V fans with 12V supply--as well as 12V fans on 5V supply. They work fine, albeit with lower airflow but a lot quieter. Heck, I've even got a 240VAC fan running from 120V--allowed me to keep my sanity, while maintaining sufficient airflow. Apparently, some of the RPi folks are taking 5V fans and running them on 3.3V.

Anent the last, any recommendations for a 40 mm DC fan that will last and doesn't cost an arm and a leg?

 

[GiGaBiTe]

While running motors at a lower voltage can be a problem in some cases, it's generally not in the case of brushless computer fans. They already run hot to begin with, when's the last time you saw a computer fan with a ventilated hub? The coils run smokin hot at normal voltages.

Where you may run into trouble are PWM fans, which have more active circuitry in them that may behave erratically at lower voltages.

 

[Timo W.]

Someone said I shouldn't do that because they draw more amps and it can burn the motor driver out. I have not done prolonged testing but does sound like a thing?

That's completely nonsense and apparently claimed by someone who never heared about the Ohm's law. At half the voltage, they will also only draw half the current. That guy probably thought it will always have the given power in watts no matter what. But that's not how things work.

The only real downside you have with undervoltage is that the fan may sometimes just not start spinning.