Hi All,

Now before I start I have to apologise if this is a totally stupid question, please don't flame me!

I am simply trying to build a controller for my fan speeds. I have tried the Maplin website and amazingly they don't appear to sell them ! I have tried RS components but they don't sell the right ones...

Where else can I buy them either mail order or in London?

Thanks very much for your help!

jp

What exactly are you looking for? A high power (several Ws) rheostat? I had problems finding any too There are prebuilt baybusses (PCMods?) available from www.theoverclockingstore.co.uk etc but they're pretty pricy.

I have built a temp dependent fan control, which was user variable too. It may be possible to alter this to use a normal resistor rather than a thermistor - thus giving complete control of the fan. This circuit uses a low power pot to control a small MOSFET.

I wanted to build a small controller for a fan (1 per 80mm Papst fan) so it seems I should be looking for 5W/100ohm from what I've read on the web....

I have to admit my electronics knowledge is fairly basic but, just like you, I resented buying the expensive baybus one at the overclocking store! You're design + idea sounds good though - did you make it yourself or is there a schematic on the web?

Glad it's not just me that can't find them rheostats!

I used the guide that is here:

http://www.heatsink-guide.com/tempcontrol.htm

while i was making it, it crossed my mind that maybe you could replace the thermistor with a normal resistor, so that the pot controlled the speed directly. Any EEs know if this is possible?

I got the bit for the kit above for about £2 from maplin, so its really cheap to just try these things out! Can get the part codes when i get home if you want them...

With the mosfet that they're using there u should be able to get a resistor to controll the temp speeds directly, after all the themistor is just acting like a varible resistor.
Personally I'd hook up a rheostat like the swiftec fan speed controller http://www.pcca.com.au/fans.html easier and just one pot to hook up.

Unless u want to be REALLY creative and hook up something like a LM317(T) it's a variable voltage regulation IC that everyone uses, just look for a search and get a datasheet, they usually have the circuit diagrams for u on them

This is the simplest, cheapest, perfectly functional LM317-based voltage regulator I've ever seen. I built several -- they work perfectly. I think an audio-taper pot makes the range of the control more useful.
http://www.overclockers.com/tips910/

- correction: NOT LM317-based...

Thanks to all of you for your help and tips!

Having had further thoughts into what I want to achieve, I think I am going to go ahead with one of each of ChiefWeasel's and MikeC's circuits. They're a lot better than some I found on the net!

Just a couple more thoughts:

1) For the thermistor controlled system: my fan will be fed power but not enought to start it for extended period as it will be used as an 'emergency' cooling fan. In all likelyhood it may come on for say a couple hours a week. Is that a problem or dangerous? Would it reduce life expectancy? Seems to me like there's heat which needs to go somewhere and I would rather my fan didn't do a meltdown!

2) The other fan will be voltage regulated but run off the motherboard. It says clearly that speed sensing does not work. Will my motherboard still be able to use it and change speeds without the speed sensing pin (which I will disconnect)?

Thanks again!

with the voltage regulation one u'd probably save a lot of effort and spend on ly a little more if u got something like a Zalman FanMate 1 on it

If the temp controlled one is normally gonna be off, then dont connnect it to a papst! They click like crazy when the voltage is below the startup voltage!

Not sure what you mean by question 2? It sounds like you want the motherboard to change the voltage? But arent you build a voltage controller?

Quokked - I already use a Zalman fanmate for one of my fans but I just quite like fiddling around and making things! I totally agree that for easiness and value for money I could get another but I quite fancy building my own! Also I find that the Zalman wires are quite short and the control knob quite small and fiddly... I know I could easily adapt that too but I juts fancy building my own!

ChiefWeasel - Thanks for the tip on the Papst I actually was thinking of using on of those! I guess as it's an emergency fan I might as well use a noisy unbranded fan I have and see what it sounds like unstarted. It'll be off 99% of the time anyway and when in use the entire system will be noisy anyway too! Thanks!

As for the other issue, well yes it does sound strange I admit! Basically my motherboard (Asus A7v333) allows me to change/reduce fan speeds a bit but the difference is quite small say a range of 20%. Thus if I set the Mobo fan speed controller to minimum the fan is still going at say 80% of maximum. I was hoping to reduce this speed to say 30% with the voltage controller. This would mean that via software I can change fan speeds between say 30% and 50%. Hope that makes sense! I know I could use a thermistor regulator but I'd rather software control this fan.....

so u're looking to control the fan from say your windows desktop? u probably could use Speedfan (don't know the link) or u'd need to build a Pulse Width Modulation (PWM) setup with a uProcessor and u'd need to hook it up to the serial port and write some I/O software or find some for yourself, (sounds complex) I haven't seen this type of direct software fan control setup on the internet but it'd be really neat if u got it going, it'd be the next generation fan bus

You're right, I use Speedfan which I have to say is an excellent piece of software. When I first got it I almost gave up as it didn't seem to work 'out of the box' as you need to set it up carefully. I did that and took a couple hours to get to know it and love it now! I think it's indispensable if your computer is compatible.

Wish I had the skills to do the PWM setup but that is well over my abilties I'm afraid!