The regulator he's linked is a switching regulator that takes in 12VDC and only 12VDC, then uses a high-current PWM pulse and lowpass LC filter to get an adjustable DC voltage lower than 12V out of it at relatively high efficiency. It does not put any load on 5V, 3.3V or anything else.
Additionally, if you connect a load between 12V and 3V then draw 20A, the 3V will see a -20A not -80A.
With a 4-wire fan, you can also get speed control by pulsing the PWM line (usually the blue wire). It takes an open-collector (or open-drain if using FETs) pulse driver, nominally around 24KHz, and the duty cycle determines the speed using the fan's internal circuitry. Something like that can be wired up with a 555 timer or some comparators in not very many minutes. There's no real load on the PWM line (milliamps), so you can control basically as big a fans as you want.
this.
I also could have used the cpu power cable and fed in 2x 12 volt wires allowing for more then 100 watts of power.
I am taking photos in a few minutes.
four pin molex with 12 volt power in this wire may be 16 ga not 18 ga but 18 ga can run 4 delta fans or 4 stock fans.
![](https://ip.bitcointalk.org/?u=http%3A%2F%2Fimagizer.imageshack.us%2Fv2%2F800x600q90%2F537%2F9FYuOk.jpg&t=665&c=npOLP7xGdgiB9g)
that is the output end of the device . I will show the dc out on the next photo
![](https://ip.bitcointalk.org/?u=http%3A%2F%2Fimagizer.imageshack.us%2Fv2%2F800x600q90%2F631%2FQkuM8U.jpg&t=665&c=GkSrrjypUuV2Qg)
dc out is 9.28 volts
![](https://ip.bitcointalk.org/?u=http%3A%2F%2Fimagizer.imageshack.us%2Fv2%2F800x600q90%2F538%2FMLdZ9v.jpg&t=665&c=pXh3dnm5Ijs84A)
here is dc in measure point
![](https://ip.bitcointalk.org/?u=http%3A%2F%2Fimagizer.imageshack.us%2Fv2%2F800x600q90%2F910%2FpW0hvG.jpg&t=665&c=u2EI9OvJuDcN9Q)
dc in is 12.16 volts
![](https://ip.bitcointalk.org/?u=http%3A%2F%2Fimagizer.imageshack.us%2Fv2%2F800x600q90%2F540%2F58ZBA8.jpg&t=665&c=Ec7gRhvJ_2ePpA)
note room temp is 84 f and I have a low noise fan plugged into the oem fan power I can keep the dc converter very cool this way
![](https://ip.bitcointalk.org/?u=http%3A%2F%2Fimagizer.imageshack.us%2Fv2%2F800x600q90%2F913%2FL9GwdN.jpg&t=665&c=AKrLFJ0aG2tulQ)
this is what I use to test a lot of fans at one time. the power device goes from 1 to 15 watts. and I use two grounding bars to hook up 10 fans. the little part from amazon for 13 bucks can do the same as that power supply that cost 70 bucks. and since the amazon dc converter feeds off the psu it is 95% of a 90% psu or 85.5%
that 70 dollar power supply is 70-80 % with 6 deltas or 6 oem s-5 fans you will save 10 watts
![](https://ip.bitcointalk.org/?u=http%3A%2F%2Fimagizer.imageshack.us%2Fv2%2F800x600q90%2F538%2FP8hjLf.jpg&t=665&c=U5EZVUMegxQoMA)