Running a Computer Cooling Fan at 5volts instead of 12volts - Damage?

[canidoit]

I placed a 12volt DC, 120mm pc cooling fan in my isolation box to prevent heat build-up and powered it using one of those computer 4pin molex power adaptors that supply both 12 and 5 volts. Problem was that the fan was running too fast that it made a vacuum sound that was too noisy. I decided to plug it in using the 5volt power instead and it quietened it to a satisfactory level.

Will this shorten the lifespan of the fan or damage the 12/5 volts molex power supply I use?

 

[abbey road d enfer]

There is the risk that 5V does not produce enough torque for starting the fan. It depends on the characteristics and construction of the fan. If you are 100% positive it starts every time, no problem.

 

[canidoit]

Do you guys believe this is safe? http://www.directron.com/12to7.html heres a more indepth article on it
http://www.hardwaresecrets.com/article/How-to-Create-a-Three-Speed-Fan-Control-without-Spending-a-Dime/496/3

Running a +12 to positive and +5 to negative on a cooling fan to produce 7 volts??

Won't this damage the power adaptor?? Don't you need a ground or negative somewhere??

I am considering trying this though, cause it might not be extracting enough air out of my isolation box at 5 volts??

 

[PRR]

WHY are you worrying about the $2 fan's health??

Or tricky connections?

The 5V won't burn it, though as the oil gums-up it will stop starting.

Another way is a resistor in series with 12V. Assuming 12V 120mA fan, that's like 100 ohms. A 100 ohm series resistor tends to give half-voltage. Not exact, because fan's V/I ratio changes with speed. But you don't need any specific voltage, you want to blow to taste. Get a handful of 33 ohm 1/2Watt resistors in series, tap one two three four or more in series with the fan until you like the blow.

You want more fun? Put two 12V fans in series across 12V. If well matched, they both take 6V and spin much slower. Now put your finger in one. The other one speeds-up! This is an interesting example of motor-action, and also tends to be more stall/gum-proof.

> Don't you need a ground

No. Ever see a battery-power hand-fan? Where is it connected to ground?

> Do you guys believe this is safe?

Generally no. It pulls current "backward" out of the 5V line. In a full PC, other 5V loads exceed the fan load, and it does work. If used on a 12V/5V supply with no other load, it probably won't.

 

[canidoit]

WHY are you worrying about the $2 fan's health??
The 5V won't burn it, though as the oil gums-up it will stop starting.

The fan is one of those gamers cooling fans with bearings so its worth more than $2. Its about $20 a pop.

Not really sure what you mean by oil gums-up? Can you expand on what you mean?? I am more concerned about the power supply burning up, like melting.

I might try the resistor avenue but after listening to it and checking out the airflow, 5 volts is not bad. I may be happy with 6-7 volts. Not sure yet...

 

[abbey road d enfer]

Not really sure what you mean by oil gums-up?

The voltage must be sufficient to produce torque that is superior to the starting torque, which includes friction. When oil ages, it tends to polymerize or "gum up", which increases the friction torque. So after some time, the fan would not start.

I am more concerned about the power supply burning up, like melting.

No risk here.

 

[CJ]

yeah wire it for 12 v with a resistor, trim the resistor so that the fan is quiet but still spins pretty good,

they make ultra quiet fans next time you are on the market

 

[canidoit]

yeah wire it for 12 v with a resistor, trim the resistor so that the fan is quiet but still spins pretty good,

they make ultra quiet fans next time you are on the market

the fan is pretty quiet, except I have it in one of those exhaust tubes so that air blows out one area, that is probably why for a silent cooling fan it is making a sort of tunnel sound.

Thanks for the response!