How to make a 12v power supply for your PC fans

[evallarta1]

I needed some fans to cool off my tank. I had a old computer that I got some fans out of and hooked one up to a old phone charger. I wasnt impressed with the out put so I figured I would fab up the powersupply from the old computer to power the fans instead. So this is how I did it.

NOTE:Make sure you know a little about electronics. There are capacitors in powersupplys and they will bite you if you dont know what your doing.

Here is my victim. A regular computer powersupply. BEFORE YOU START,MAKE SURE ITS UNPLUGGED!!!


First you have to open up the case. Mine had 4 screws on the top that I took out and pulled of the cover. There was a fan on the cover that I unplugged and put to the side. This is what it looks like inside


Next I took off all the zip ties and cut off all the connectors. Now for ME I need 2 12 volt supplies. So I pulled aside 2 yellow and 2 black wires. Yellow is +12 volts and black is ground or 0v. You can see where I put them aside. You will also need to pull the single green and a additional black wire aside. Then I cut the rest of the wires short so I could fit it in the case. The reason why I didnt cut the other wires off is if I need other equipment powered I have the option.


Now what about that green wire you ask? Well if you were to plug in your powersupply and try to turn it on it wont. The green wire is normally plugged into the motherboard and when you push the on button on your computer the green wire is what tells the powersupply to turn on. So you solder the green wire to the extra black wire you put aside and now your powersupply will always turn on when you hit the switch.
Note: If your powersupply does not have a switch on the back (mine did) you can attach the green and black wire to a toggle switch and this will allow you to turn your powersupply on and off. I also folded the spare wires in half and zip tied them together so they would fit in the case.


Once I finished that I tucked in all the wires except the 4 that will feed my fans. I made sure the wires wouldnt interfere with the fans spinning. I also changed one of the fans to blow out so its not constantly sucking in salt spray.


Finally I plugged in the cover fan and put the cover on. I hooked up the fans and plugged it in and turned the bad boy on. Worked like a charm.


I personally think using a computer powersupply is a much better option then using a phone charger. Especially when there's one just sitting around!

[chipmunkofdoom2]

A good idea, but make sure the power supply has been sitting for a lot of time without use. Power supplies can hold some pretty powerful charges for a while after usage. Good how to though, now I have a use for all those crappy power supplies that come with my cases

[chipmunkofdoom2]

Now, question: are ALL the yellow cables 12V? I have this power supply sitting here and it has a total of 5 yellow cables, one bundled with the 20 pin mobo connector, two going to molex and floppy power, and two going to the 4 pin connector that I believe is for P4s. Can I use all 5 of them for fans?

[Frankie]

Very interesting! Well done.

[mps9506]

Now, question: are ALL the yellow cables 12V? I have this power supply sitting here and it has a total of 5 yellow cables, one bundled with the 20 pin mobo connector, two going to molex and floppy power, and two going to the 4 pin connector that I believe is for P4s. Can I use all 5 of them for fans?

I think you just want to use the ones going to your molex connectors.
You can run multiple fans in series I believe as most of those power supplies should handle up to 10 or so amps on those rails.
Don't quote me, I'm pretty weak when it comes to electronics

[evallarta1]

Yes every yellow wire is a 12v supply, so you can use any or all of them.

Red = +5V,
Blue = -12V,
Orange = +3.3V,
Purple = +5V Standby,
Black = Ground (0 V),
White = -5V,
Yellow = +12V,
Gray = power is on,
Green = Turn DC on

If you need more amps. Take more then one wire (ie 2 or 3 yellows) and twist the ends together. Then take a equal amount of black wires and do the same. I tried a little experiment where twisted 2 yellows together and hooked it to a fan (increased the amps) I then hooked another fan to a single yellow. The fan speed was the same. So Im just using one yellow per fan.

[chipmunkofdoom2]

Ah okay. Good info, thanks! I've often wondered what each one of those wires did

[njm92383]

another thing would be you could to newegg.com and buy one. The fans are just plug and play.

[Luukosian]

If you need more amps. Take more then one wire (ie 2 or 3 yellows) and twist the ends together. Then take a equal amount of black wires and do the same. I tried a little experiment where twisted 2 yellows together and hooked it to a fan (increased the amps) I then hooked another fan to a single yellow. The fan speed was the same. So Im just using one yellow per fan.

The fan is only going to draw as much current as its load dictates.... hooking up two wires(which are from the same source in the power supply anyways) isn't going to make a difference. That is why PC power supplys are arranged so everything is connected in paralell, that way everything is supplied with the same voltage but the current differs.

The average 12 volt rail on a psu is rated for 20 amperes....so you could run a lot of those little fans.

I don't see why a standard 12V transformer wouldn't put out enough current to run a simpe computer fan. Unless it is a 6V or you had several connected in series or something I'm not sure why it would run any slower than using the 12V rail on a power supply.

[freddyk]

This is a very interesting thread.

Luukosian - What you said about the 12V transformer makes a lot of sense to me. It seems simpler and possibly more efficient than using a whole PC power supply. Could it be as simple as taking a 12V transformer from some long lost gadget and then string 3 or 5 fans onto it?

[gunster1]

just in case, you should definitely cap the end of the cut wires that you are not using. they could cause a fire if they short out. and i am sure you do not want anything like that to happen.

[jkburton1s]

is there an easie way to put pc fans on a canopy setup so they come on with the mhs/??? do you just add a resistor???

[StirCrayzy]

This is a very interesting thread.

Luukosian - What you said about the 12V transformer makes a lot of sense to me. It seems simpler and possibly more efficient than using a whole PC power supply. Could it be as simple as taking a 12V transformer from some long lost gadget and then string 3 or 5 fans onto it?

YES !! This is how i keep my entertainment center cool !
As long as the output is 12 volt, then your fan quantity is only limited by the max amperage of the supply.
In my entertainment Center, i have 6 fans on a 12v 3a transformer that used to charge my wireless headphones.
I like the power supply option, if your gonna be running a ton of stuff (or BIG fans and lights) with it, but for only a few fans, its quite a waste IMO.


Good info though.

[jkburton1s]

isnt there something simpler??