Wiring a case fan - please help

By andygibbs ยท 13 replies
Mar 4, 2005
  1. Hi,

    I've just upgrade my power supply and thought that it would be a good idea to take the 8cm fan out of my old unit to use as a case fan. When i opened up the unit, i found that the case fan only has two wires coming out of it, a red 1 and a black 1. These are soldered directly into the PCB of the circuit. I need to know how I can get these to connect into a standard molex or fan connector. This is what i've thought of so far:

    Red ---------- splits to Red molex and Yellow molex

    Black -------- splits to Black molex and Black molex

    Can anybody tell me whether or not this will work and if not, what else I can do to get this fan to work.


  2. RealBlackStuff

    RealBlackStuff TS Rookie Posts: 6,503

    Look for any indications in the sticker on that Fan. There must be a model number or something which might say 12 or 5. Probably 12volt.
    In the molex connectors, yellow=+12v, red=+5v, black=ground.
    NEVER EVER connect the red and yellow together, your powersupply will DIE.

    To try out that old fan, with your case open and the PC on, connect the black fan-wire to one of the black molex wires (either will do) and connect the red fan-wire to the red 5v molex. If the speed is normal, fine. If it is real slow, try the red-fan on the yellow-molex, but just hold it loose against it. If it wants to 'take off', it is probably a 5v fan. Watch your fingers though, those blades are sharp!
  3. ripken204

    ripken204 TS Rookie Posts: 139

  4. speedy266

    speedy266 TS Rookie Posts: 23

    2 of my 4 case fans are from old power supplies. I will soon upgrade all 4 to really good quality 80mm case fans, but im still looking, most move about 40CFM of air, ive found with that moves 78CFM of air which would be sweet with a fan speed controller that slips into the A Drive slots, id have to splice all 4 into one knob, but that might slow down all the fans, id like a fan that runs off 12 volts and spins at 4500+rpm all the time moving 65+ CFM of air.

    I made a 24Volt Source with 16 batteries and held the spliced wires of the case fan on the terminals and it spun really fast and moved ALOT of air, but it probably wouldnt have a long life span
  5. wiscountryboy

    wiscountryboy TS Rookie Posts: 60

    hey i donno if this will be any help but oh well here i go.....i recently scraped 4 super old computers for like 1991 and found that the cpu fan was on a 4 pin molex connector so all i did was splice the red to the red and the black to the black... i got decent fan speeds but i dont know if they were as fast as they could of been
  6. speedy266

    speedy266 TS Rookie Posts: 23

    Yah i my old pentium 1, 133mHz ran its small little cpu fan off the 4 pin connector and it was to connected to the red and black which is 5 volts. You could make it more fast in the yellow and black, which is 12 volts, but the fan wasnt designed for it and its small so 12 volts would probably rapidly shorten its life, id suggest 80mm case fans all the ones ive seen run off 12 and move more air, new ones would have a better fin design and lighter blades for more rpms and probably move more CFM of air.
  7. wiscountryboy

    wiscountryboy TS Rookie Posts: 60

    yup yup and as long as you use power from the power supply you should get enough power if you take it from the yellow and black and you are grounded so things shouldnt fry on you.... :hotbounce
  8. Mictlantecuhtli

    Mictlantecuhtli TS Evangelist Posts: 4,345   +11

    You can get 7 volts from ATX PSUs by wiring fan's negative wire to +5V (red) and positive wire to +12V (yellow).

    Better than 5V and less noisy than 12V.
  9. wiscountryboy

    wiscountryboy TS Rookie Posts: 60

    hey instead of wiring u could get a new fan and buy one with a "silencer" this limits the voltage that the fan gets.....i got one with my Zalman fan
  10. speedy266

    speedy266 TS Rookie Posts: 23

    Hey Mictlantechuhtli thats pretty cool, didnt know you could do that. I run a tiny bulb from a xmas light wire with the wire ends that bend up and u slide it into its socket. I usually stick the 2 light prings into the red and black for 5 volts as they do not last very long under 12 volts. Give my case a nice color shine.

    Is there anyway to get more than 12volts from the 4 pin wire connectors by somehow combining the 5V and the 12V, i thought there was only 12V and 5V, but now u can get 7V to.
  11. cmy6800

    cmy6800 TS Rookie Posts: 20

    The way PSU's are designed, it would be nearly inpossible to combine the 12 and 5 volt rails for 17 volts. In fact, lets just go ahead and throw out the .01% possibility all together and say it is just impossible. If you connect both the 12 and 5 together, you will still have 12. As previously mentioned, if you connect the 12 to pos and 5 to neg, you get 7 since you have 5v resisting the 12. Even though there isn't anything really wrong with that approach, I wouldn't reccomend it. IMHO, a better solution would be to use a potentiometer or thermsistor to limit voltage. For those who have no freakin idea what I'm talking about, a potentiometer is what all fan controllers use. It is a variable resistor. On the other hand, a thermsistor is a resistor that is sensistive to temp. If it were me, I would go the thermsistor route. Fully automatic and, if you do it right, it is always the "right" speed. If you really want to do something cool, you can wire it in such a way to where you can choose how you want it to run. Parts needed per fan would be a potentiometer, a thermsistor, and a 3 selection knob or toggle style switch (abc switch). Positive goes to the pos on the switch. Then, three seperate leads will come off the switch to the respective areas. One, directly to the fan (full on), another passes through the potentiomenter (manual adj.), and the last goes to the thermsistor (auto adj.). There you have it kids. What is better, is that you can mount all this to a 5.25 slot cover and totally make it your own. Add to the cover a simple temp monitoring circuit, and you have one hell of a cool controller (that does more than other controllers) for cheap. Well, this post is quite long enough. Hope this helps someone.
  12. wiscountryboy

    wiscountryboy TS Rookie Posts: 60

    so then how much would a temp resistor cost me and a good fan controller?
  13. cmy6800

    cmy6800 TS Rookie Posts: 20

    Check out your local radioshack. You'll want to make sure you get the right parts if you so choose this project. Pick up a soldering iron too if you don't have one.
  14. wiscountryboy

    wiscountryboy TS Rookie Posts: 60

    alright i will do that.....
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