Powering a computer fan to cool the tower - troubleshooting

I'm hoping to get some advice from someone who knows more about electronics than me.

I bought a simple 50 mm computer fan (12V DC) that used a molex plugin (4 pin). I clipped it off so that I only have the hot lead +12V and the ground going to the fan. Then, I bought a AC to 12V DC adapter. Clipped off whatever connector was on there, stripped wires on each device, twisted together (hot to hot, ground to ground). Plugged it in to the wall and... nothing. The fan does not turn on.

Did I do something wrong? Or do I possibly have a faulty component?

The fan should have a current rating on it in milliamps (mA) or a power rating on it in watts (w).

You have to make sure the power supply will put out enough juice to drive the fan. So if the fan says say 500 mA, you would need the power supply to be rated at or near 500 mA to drive the fan.

It is always possible you have a bad component. Does the fan react at all when you connect it?

Also try reversing the wires.

I tried reversing the wires. Also, the supply gives .5 amps. The fan needs about .1 amps. I'll probably go to the computer shop tomorrow and put the power supply up to a volt meter thingee. If that works, I'll ask them to replace the fan.

Its a 4 pin fan, you need to connect the other two wires together (the ones that are not power) for it to turn on. Some fans have a fail safe, if they are connected wrong they will not turn on (positive to negative and negative to positive), others will just spin the other way.

But your problem is that you dont have those other two wires connected to each other. Connect them and you will be just fine. That is the signal that tells the fan to turn on.

Brewin_CRAZY said:

Its a 4 pin fan, you need to connect the other two wires together (the ones that are not power) for it to turn on. Some fans have a fail safe, if they are connected wrong they will not turn on (positive to negative and negative to positive), others will just spin the other way.

But your problem is that you dont have those other two wires connected to each other. Connect them and you will be just fine. That is the signal that tells the fan to turn on.

Click to expand...

It seems to me that in the molex thing, the four wires don't contact each other at all.

So, the molex is...

+5V (red)
Ground (black)
Ground (black) (had a black going to fan)
+12V (yellow) (had a red going to fan)

Now, connected to the Ground next to the 12V and the 12V there was a black and red wire respectively. It is my understanding that these wires never had any contact with the other ground and the 5V wire.

But, please let me know if my understanding is wrong!

Thanks for all the help so far.

So i decided to tune out the fact that you said molex. I was assuming it was a 4 pin connector for the motherboard (i.e. CPU fan). I have never used that type of comp fan before, however it should work just fine if you connect it the way you have it. Sorry for the confusion.

I would assume that just 12V to a ground connector should work. Assuming the fan spins freely when you spin it by hand it should be functional. I would connect the 12V and each ground then just start messing with the wires, at 12V, prob like .5 A you wont fry anything. Just start messing with the wires, I have done this many times to try to get things to work. 12V is nothing, the fan may need that 5V hooked up, but it shouldnt, try just connecting the 5V to one of the grounds (while the 12V is powered) and see if that works. Like I said, just mess with it, those fans are pretty robust.

If all else fails take it in to the comp shop and tell them you couldnt get it to work.