• Welcome to Overclockers Forums! Join us to reply in threads, receive reduced ads, and to customize your site experience!

DIY Fan Controller for PWM Fans

Overclockers is supported by our readers. When you click a link to make a purchase, we may earn a commission. Learn More.
Hey Dave, great article, nicely done and well consolidated too ! :clap:

Love the intro, and those illustrations too, thanks. :thup:
Dave, really happy to see this article on the frontpage - great read, very clear, and a cool project spawned out of the forums. Getting the fans to you was no problem, and I'd be happy to do it again anytime! Thanks for putting this together!
Hell yeah... Great write up. I'm sure there will be plenty more controllers built because of this; I, for one, am going to be putting my bread-boarded controller down on perf-board pretty soon. And once the first one is all done there will be a few more coming behind it.
Nice work and write-up!

Brings back great memories of when men were men, and we had to make our own controllers or do the 5V/7V tricks. (Back before Zalman and everybody else flooded the market with pre-made controllers. :))

Very nice design. Best -- Paul
I highly recommend getting one of these fans for kicks :D

Paul - thanks, and it's nice to see somebody else putting Dundee on the map!!
Is it possible to replace the manual control with a thermistor and let the temperature control the fan speed? (with a rheostat as an adjustment). haven't been able to find such a circuit anywhere :( and commercial offerings are way too expensive.
I should think that would be possible.

Two configurations to think about:

(1) rheostat + thermistor in series: net resistance is additive

(2) rheostat + thermistor in parallel: net resistance is R1 * R2 / (R1 + R2)

Option (1) involves soldering your thermistor after or before P1.

Option (2) would be a matter of soldering the thermistor in parallel with potentiometer / rheostat R1.

There are pros and cons to both to think about. -- Paul
It would be possible, but I think your dealing with two kinds of temperatures. One inside the case and the temperature of the CPU Cores. Since you could only go off of the core temperatures for your CPU, you would have to tap those temps from the Motherboard. In that case a lot of the newer motherboards use PWM to control their fan circuits, especially the higher end ones.

The problem (you will find out if you read my whole thread) is with the stepping of those PWM circuits. This is where this controller comes in. In all honesty, you really only need about 3 or 4 speeds for this fan. Low/Med/High would work in almost all cases, except that different fans at this speed exhibit noises that can only be eliminated if you turn them up or down ~50 RPMs. In essence your are tuning them. It would be too much work to try to tune a 3 speed controller.

I run my fan daily at about 900 RPMs. I turn it up to about 2000 while gaming and then I turn it to 6000 while benching. All of these are +/- 50-100 rpms. You just can't do that with switches. Well actually, you could... on a non PWM, but then you would deal with Undervolting which would also produce annoying noises.

I could have built a thermistor into this circuit, but PWM really was probably overkill for most computer users, and a thermistor controlled PWM would be definitely overkill. Essentially a thermistor is just a variable potentiomter, just like the 10 or 100k Poti used in this circuit. So one would just replace the Poti with the thermistor.... Problem solved. You just have to tune it/
Just came out of my mind on one simple thing, Lenny, how many fans maximum that controller capable of driving ? Ever tested 4 of that beasts altogether ?

This is interesting since as original circuit without the booster (inv sch buffer) couldn't drive even one as Brutal experience.
I'll get round to it soon bing. Problem with four fans is the enormous power draw of nearly 200 watts and 14-16 amps.

I think I'll buy a cheap PSU specifically for testing the fans - don't want to short my system again!!