Pro/Forums - View Single Post - How to calcualte how much power an undervolted fan will draw

Butcher · 01-23-2005, 11:43 PM

Assuming you don't stall them, power drawn is propertional to the cube of the speed of the fan. Speed is proportional to voltage.
So at 12V, you draw 0.5^3 as much power as at 24, which is 3.25W.
At 6V the fan will have stalled. In fact given 12V is the minimum voltage, you'll not really be able to adjust them much off a standard PC supply as they'll stall at around 10-11V.

According to specs the maximum you can pull off a MX212 fan header is 750mA, at 12V that's 9W. So you can run 2 fans off one header, though given you won't be able to adjust them, you won't really see much benefit over just hooking them directly to the 12V.

01-23-2005, 11:43 PM	#2
Butcher Thermophile Join Date: May 2001 Location: UK Posts: 1,064	Assuming you don't stall them, power drawn is propertional to the cube of the speed of the fan. Speed is proportional to voltage. So at 12V, you draw 0.5^3 as much power as at 24, which is 3.25W. At 6V the fan will have stalled. In fact given 12V is the minimum voltage, you'll not really be able to adjust them much off a standard PC supply as they'll stall at around 10-11V. According to specs the maximum you can pull off a MX212 fan header is 750mA, at 12V that's 9W. So you can run 2 fans off one header, though given you won't be able to adjust them, you won't really see much benefit over just hooking them directly to the 12V. __________________ Once upon a time, in a land far far away...