24V Cooler Overvolting

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Severe fan overvolting – not recommended but interesting. – Damir Lukic

NOTE: Overvolting any device and operating it outside of its specifications can lead to premature failure very quickly. Neither the Author or Overclockers.com will be held responsible for any damages consequent to this article. It is presented for information purposes only.

Hi to all of you, good people! 🙂 Greetings from Croatia (the land of healthy cows, and crazy people!) :)))))))))

Here it comes, something that I haven’t seen before anywhere on the net!

Ladies and gentleman, I’d like to introduce you to 24V cooling. My own idea (but, I must say that I’m definitely not the only one who came with this idea!). 🙂 Greetings to all of you who know about this little secret. 🙂

The story goes…Once, a long time ago, I discovered a label on my power supply that said something like:

  • +12V : 8A
  • +5V : 20A
  • -5V : 0.5A
  • -12V : 0.5A

And, then I first saw that my power supply has negative (-) voltages! I couldn’t believe my eyes! But… I knew that there should be much work on finding these negative voltages. Pardon me. These are not voltages, it’s called electric potential! So, now that we’ve cleared this, we can go further.

So, the work started. I took my cooler, and first thing that was tested were those Molex connectors for disk-drives (Yellow|Black|Black|Red).

The cooler worked just the way it always worked, so I should try to find these negative potentials somewhere else. And then I saw it: AT power connector for motherboard! I just smelled that my search is over! 🙂

Now, the only thing I should do was to test all the wires (12 wires on AT, and 20 on ATX). With the AT connector it was easy – I knew that the yellow wire was +12V (logical thinking), red wire was +5V, and black wires was GND (ground, it’s called ‘reference potential’). I think I should later explain some terms. Let me proceed… So, then I discovered what other wires were. White wire was -5V and blue wire was -12V. Orange wire? Maybe 3.3V, but I’m not sure, it’s on AT connector. On ATX it’s 3.3V.

So, I’ve found everything I needed for the job to be done! 🙂 +12V and -12V! OK, now, the wiring job. I just cut the wires from the cooler, and connected them onto the AT power connector. Yellow wire from the cooler was connected to the yellow wire on connector (+12V), and black wire from the cooler was connected to the blue wire on the connector (-12V).

When I turned my computer on, the thing was so loud that I thought I had a vacuum cleaner connected! 🙂 It was little 486 cooler.

Now, one crucial thing! What is the ground?

Ground is not 0 Volts! Ground stands for reference potential! So, if you use the -12V potential as ground (reference), voltage is counted from ground to it’s original potential. If you want to count +12V from ground connected to -12V, let me see… It’s, YES, IT IS! IT’S 24V!

Black wires from the power supply are at potential 0V, and they are ground, so every voltage goes relatively looking from 0V! (please, if this explanation is not good enough, contact me so I can try to explain it again)

Tip: You can get 17V from an AT power supply! Connect the yellow wire from the cooler to the yellow wire on the AT connector, and the black wire from the cooler to the white wire connector. This should give you 17V!

Now, how does this work with an ATX connector? Just the same way as with the AT connector. The wires are the same colour, and you won’t get into trouble finding them. Anyway, look at this picture:


But I forgot. These new coolers have so called ‘RPM sensor’ on them! 🙂 Well, this is a lie. They do not. The motherboard has the RPM counter, and it counts impulses that the cooler sends to it. How it works; I won’t bother you with it now (contact me if you want details, or search the net).

Anyway, there are some things left to say about the Molex cooler-connector for the motherboard. It has three wires on it, right? Well, one is red, one is black and one is yellow or blue. Things here are not quite the same as on the old coolers. Here we have red wire for +12V, black stays as it always was – ground, and yellow/blue wire is this – ‘sensor’. So, you’d have to get red and black wire out of this connector (cut them!).

Now, the red wire from cooler should be connected to the yellow wire on the ATX power connector, and the black goes to the blue wire on the ATX connector – that’s 24V. Plug that leftovers of cooler-connector onto motherboard, and watch how the rpm increased! 🙂 I had 50% speedup! And about the airflow, I won’t talk about it! 🙂 It was a vacuum cleaner!

Note that cooler would be pretty loud when connected to 24V! And, guess what – you can decrease the voltage to the values as stated here:

V(high) – V(low) = V(output)

12V – 3.3V = 8.7V (red-yellow, black-orange)
12V – 5V = 7V (red-yellow, black-red)
12V – 0V = 12V (red-yellow, black-black)
12V – (-5V) = 17V (red-yellow, black-white)
12V – (-12V) = 24V (red-yellow, black-blue)
5V – 12V = -7V (red-red, black-yellow)
5V – 3.3V = 1.7V (red-red, black-orange)
5V – 0V = 5V (red-red, black-black)
5V – (-5V) = 10V (red-red, black-white)
5V – (-12V) = 17V (red-red, black-blue)
3.3V – 12V = -8.7V (red-orange, black-yellow)
3.3V – 5V = -1.7V (red-orange, black-red)
3.3V – 0V = 3.3V (red-orange, black-black)
3.3V – (-5V) = 8.3V (red-orange, black-white)
3.3V – (-12V) = 15.3V (red-orange, black-blue)
0V – 12V = -12V (red-black, black-yellow)
0V – 5V = -5V (red-black, black-red)
0V – 3.3V = -3.3V (red-black, black-orange)
0V – (-5V) = 5V (red-black, black-white)
0V – (-12V) = 12V (red-black, black-blue)
-5V – 12V = -17V (red-white, black-yellow)
-5V – 5V = -10V (red-white, black-red)
-5V – 3.3V = -8.3V (red-white, black-orange)
-5V – 0V = -5V (red-white, black-black)
-5V – (-12V) = 7V (red-white, black-blue)
-12V – 12V = -24V (red-blue, black-yellow)
-12V – 5V = -17V (red-blue, black-red)
-12V – 3.3V = -15.3V (red-blue, black-orange)
-12V – 0V = -12V (red-blue, black-black)
-12V – (-5V) = -7V (red-blue, black-white)

Well this is the table (at least, should be a table!). 🙂

It’s a complete list (without 0V output voltages) of all the voltages you can get with ATX power supply.

Is it safe? I believe so. I haven’t burned any of my coolers. But, you might hear strange sounds after a while, like the sound that bees produce – a Bzzzzzzzzzzz sound. Well, get some grease and open your cooler. Get it off the heatsink, remove the sticker, put some grease in the middle, place that sticker over it, connect the cooler to the supply, and listen. The strange sounds should vanish, and you can mount your cooler on again.

Will it burn? No, it won’t. The design of those fan motors is very good. They are brushless, after all! They operate like stepper-motors with 2 steps, and the principles of their work is very hard for me to explain. My English is not that strong. Maybe I could try to write an article about it, just informative, nothing very in-depth. 🙂

Well, that was the whole story about 24V cooling, and now, about my achievements! 🙂

Intel P100@150/166: This was the first CPU I overclocked with this new cooling. It POSTed, loaded DR-DOS, and I was able to play games, but when I tried to load a game in CM97/98, it stopped. So, I wouldn’t call it rock-stable.

AMD K6/266@300/333: Rock-stable, I even played Fallout on it! It was a good CPU! That was the times… Oh my…

Cyrix M2/225@300/333: Rock-stable. It still works in my parent’s computer at home, and operates at 300 MHz. Rock-stable with 12V cooling. 333 MHz was rock stable only with 24V cooling, not even 17V helped here!

Intel Celeron333A @ 375/500/515: Rock-stable at 375. POST but won’t boot into Windows on 500 and 515MHz. 🙁 I even tried frying it at 3V, but no good. 🙁

Intel Celeron300A @340/450/466:
Rock-stable all the time. It was the good old Celeron300A! 🙂

Intel Celeron400A @450/500:
Rock-stable, even with 12V cooling! 🙂

Intel Celeron433A @488/541:
Rock-stable with 12V cooling. That’s my current CPU, and I am thinking of frying it to 2.4V and 24V cooling, and then it could maybe go to 600MHz… Who knows. 🙂

Well, as I don’t have money for the new stuff, I am stuck with this 433 Celeron. Now, I’d like some feedback about what you were doing with your CPUs, especially AMDs!

Thanks again for reading all this, and I believe it helped you, or at least gave you new sights about cooling. At least you learned what ground is! 🙂

Greetings from Croatia, and see you soon! :))

Damir Lukic – Croatia

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