Why does my computer fan keep swiching direction?

Im trying to power a computer fan with batteries for a project. The fan wasn't turning so i tried upping the voltage. Ive tried one two and tree 9 volt batteries in series to make it turn. It worked best with two but the bizarre thing is that ever second or so it stops and sometimes switches direction. the fan has 3 leads red white and black. im powering red and back is ground the whit i think is a fan speed information wire of some kind. im not really sure. Any one have any ideas?

iceng6 years ago
The fan is probably a 12 VDC unit
and was still working at 18 VDC
But at 27 VDC you are either overheating it or
have damaged the electronics.
Did you know the power a fan requires increases as the speed3.
That means doubling speed will quadruple the power used

Be careful the thunderbolt god may smart U for abusing electronics.

its smite* not smart, smart is not a doing word, its a state of being!

now, as for your problem there may not be sufficient current coming from the batteries, try running some in parralel!, or adding a 40v capacitor to the fan, because some fans require a boost charge before they can start.

also, i think that your fan is ac powerd, because they generally dont use 3 pins . ground is ground for ac, red positive and black negative, unless it is designed and have some IC inside to switch polarity for an emergency cool down, as i beleive, where the fan blows air out, if it were but would risk also sucking dust in as it wouldnt be passing through whatever is used to keep the dust out.
short of that i have no clue , but it is meant to work at 12v , never raise the voltage above what it is recomended as it will burn the wires, and in the case of brushed motors, will generate allot of sparks, generating corrosive ozone and nitrous oxide, which will quickly burn away the carbon brush!
But smite implies death of the abuser :-(
My thunderbolt god applies a sharp non-lethal electric shock.
So the abuser smarts from the punishment and
simultaneously learns from the experience ;-D

I know I didn't use the word correctly,
But then the thunderbolt god wre never meant to be   :-)
I like your page...   A
Most or at least many PC fans have three pins, two for supply and one for speed sense.