PWM fancontroller

[Alexandr0s]

Today the parts for my PWM fancontroller arrived. After a few tedious hours of soldering (which made me look like WL's avatar), the controller was finished. Here is the current version (will do more when I get new parts):



(It's late and I have a bad camera, so don't be mad about the quality ).

As you can see, it's a fairly straightforward design, but because I made some stupid decisions during the purchase of the parts, I ended up having 2 1mm SMD capacitors, which are a real PITA to solder properly .

The fancontroller is PWM controlled, designed for normal 3-pin fans (here is a quick explanation of PWM fancontrol), based on the NE555 timer as an astable multivibrator, which is a design used in some professional fancontrollers as well.
The design is based on this schematic (source):


Theoretically the Mosfet I'm using is rated for 9.2A, meaning I can completely use the capacity of a single Molex line (rated for 5A). Of course, it gets rather hot, even when using one fan, but I'll get a nice big heatsink for it later .
Here you can see it controlling 2 fans:



There are still some improvements I plan on doing:

• The Mosfet will be fitted with a big heatsink, because it's getting rather hot right now.
• The layout will be changed, to allow the heatsink and the fan header to fit properly.
• Of course, the SMD components will be replaced by components that are easier to solder.
• The final circuitry will be on a printed pcb, which I will also create myself.
• The potentiometer will be replaced, because it currently lets the fans run at 100% when it's only at 10% voltage. Also, I want one with a big knob .

So far my little fancontrolling experiment. Of course, I'll keep everyone updated as this progresses further. Feel free to ask any questions in the mean time . Hope you all like it.

[OldChap]

I'll be watching

I'm curious to know whether you intend to play with it some....trying out high and low frequency pulse and with/without the output capacitor fitted and which fans too.

[Alexandr0s]

I definitely will, though for the next few weeks, I won't have time because of exams.

I think that if I remove the output capacitor, the signal will be less flat, and I might get some ticking from the fan.

Also, I already played a bit with the frequency by accidentally switching the 0,1nF and the 10nF capacitor. It cause a high pitch whine in the fans, which I think is caused by the lower frequency of PWM signal. This possibly caused it to come within audible range for humans, which caused the whine. It's fun playing with things like that :P.

[fgw]

The Mosfet will be fitted with a big heatsink, because it's getting rather hot right now.

this shows, the mosfet is not switching off completely! ran into the same issues when i played around with PWM. fortunately i had an oscilloscope at hand which proved my doubts.

The potentiometer will be replaced, because it currently lets the fans run at 100% when it's only at 10% voltage.

as the mosfet is not switching off completely, there is no way to control the fans down to lower speed.
also different fans behave differently. depends an load and the fans internal circuitry. there already transistors build into the fan which are switching the coils to allow the fan to rotate. this is by design of the brushless motor used in the fan. guess this circuitry gets messed up if fed with PWM instead of a continuous voltage.

i finally gave up on PWM and decided to go the linear voltage control route.
parts already arrived, but unfortunately i'm too busy right now. hopefully i can start my project during the next few weeks ...

anyway, congrats on your first PWM controller!

[jalyst]

Nicely done, a little limited in functionality for me, but no doubt you've learnt a lot from the whole experience!

[CrazyNutz]

The lenear route is much easier to implement using a lm317, however (depending on the load) it will get very hot, much hotter that a proper PWM implementation.

[Alexandr0s]

Could someone please explain the problem of a not completely closing mosfet to me? I don't think I'm getting it :P. What exactly causes it, and what are the effects?

[fgw]

Could someone please explain the problem of a not completely closing mosfet to me? I don't think I'm getting it :P. What exactly causes it, and what are the effects?

the idea of PWM is to have the mosfet either completely switched ON or completely switched OFF. the power and thus rpm of the fan is controlled by the duty cycle of the signal.

in theory:
50%on/50%off -> 50%rpm
25%on/75%off -> 25%rpm
10%on/90%off -> 10%rpm

anyway, the mosfet should know just two states, either completely on or completely off at any given moment!

in both states the dissipated power (heat of the mosfet) should be almost 0 (ZERO):

when switched OFF this is obvious: no current is flowing through the mosfet while all 12V are across the switched off mosfet leaving 0V for the fan. this results in 0A * 12V = 0W for the mosfet to transform into heat.

when switched ON there is of course current flowing through the mosfet (lets say 2A just for fun) but as the mosfet has a very low Ron (resistance when switched ON) there are just a few mv (may be 20 milli volt) across the mosfet leaving almost all 12V for the fan. now, the power the mosfet has to transform into heat is 0,02V * 2A = 0,04W which is almost nothing!

thats why - if PWM is working as expected - the mosfet should not even be warm!

in your circuit, unfortunately the mosfet is not switching off completely, thus there is a small amount of current flowing even when you dial in lets say 10% pwm. this results in having some voltage across the moset and some voltage on the fan. add the current which flows through the fan now an the mosfet starts to heat up, while the fan refuses to regulate to lower rpm.

cant tell you the reason for this behavior, its just the explanation for the unexpected heat on the mosfet. may be another mosfet type, or different gate voltage might help. but as said before, i stopped playing with PWM and moved on to linear voltage control.

getting rid of the heatsink would be the main advantage of PWM to me. if i need a heatsink for the mosfet i can even use linear voltage control which requires a heatsink by design. and of course i even wont run into rpm reading problems or unwanted switching noise with linear voltage control.

give me some time. will post my solution as soon as its ready. some of my ideas are:

• microcontroller based
• usb interface to system
• read tempsensors already available in the system
• read external DS1820 sensors
• communicate with rivatuner
• control fans via motherboard pwm headers
• low power (1.5A) and high power (3A) outputs (although i don't think anybody needs 3A)

and much more

[Alexandr0s]

Thanks for the explanation. I'll do some reading about that mosfet and I'll see if there are options ^^.

Just found this. According to this site, there might be some current flow when using pulse to control the mosfet. Also, getting the V-gs (gate to source voltage) to 5V will make it more efficient. I'll measure the voltage and will try adding resistors accordingly. I'll continue to do more reading .

[jalyst]

when switched ON there is of course current flowing through the mosfet (lets say 2A just for fun) but as the mosfet has a very low Ron (resistance when switched ON) there are just a few mv (may be 20 milli volt) across the mosfet leaving almost all 12V for the fan. now, the power the mosfet has to transform into heat is 0,02V * 2A = 0,04W which is almost nothing!

thats why - if PWM is working as expected - the mosfet should not even be warm!

in your circuit, unfortunately the mosfet is not switching off completely, thus there is a small amount of current flowing even when you dial in lets say 10% pwm. this results in having some voltage across the moset and some voltage on the fan. add the current which flows through the fan now an the mosfet starts to heat up, while the fan refuses to regulate to lower rpm.

cant tell you the reason for this behavior, its just the explanation for the unexpected heat on the mosfet. may be another mosfet type, or different gate voltage might help. but as said before, i stopped playing with PWM and moved on to linear voltage control.

getting rid of the heatsink would be the main advantage of PWM to me. if i need a heatsink for the mosfet i can even use linear voltage control which requires a heatsink by design. and of course i even wont run into rpm reading problems or unwanted switching noise with linear voltage control.

give me some time. will post my solution as soon as its ready. some of my ideas are:

• microcontroller based
• usb interface to system
• read tempsensors already available in the system
• read external DS1820 sensors
• communicate with rivatuner
• control fans via motherboard pwm headers
• low power (1.5A) and high power (3A) outputs (although i don't think anybody needs 3A)

and much more

Fascinating, I'm intrigued to hear that you've given up on PWM...
I didn't realise there are RPM reading problems or switching noise assoc. w/PWM!? (at least more so than LVC)
What are the main reasons you don't feel PWM should be part of your project?

I've got some requirements in a controller, but I'm not sure what you've planned will satisfy them all!?

P.S.
apologies Alexandr if this is hijacking your thread somewhat :|

[fgw]

I didn't realise there are RPM reading problems or switching noise assoc. w/PWM!? (at least more so than LVC)

• motor ticking noise when running at low PWM frequency. guess thats why intel specs use about 25kHz PWM frequency for PWM fan control.
• high PWM frequency on the other hand, interferes with rpm readings as the fans internal rpm reading circuit is switched on and off at the PWM frequency, thus the rpm output is switched at the PWM frequency too. this interferes with the regular rpm pulses resulting in erratic rpm readings. this problem is primarily at lower rpm!

What are the main reasons you don't feel PWM should be part of your project?

as said before, i played around with it but was not able to control my fans the way i expected. the results varied from fan to fan. same fans could be controlled in the range from 80% up to 100% by varying PWM duty cycle from 5% to 10%. everything above 10% PWM duty cycle resulted in 100% rpm. thats not the way its supposed to be.

of course, all this problems are related to 3-pin fans only. bus as the PWM versions of gt's are not available till now i will focus on 3-pin fans.

anyway, my controller will definitely be able to use PWM control on 4-pin (real PWM) fans also.

[CrazyNutz]

1). You might try placing the diode between the j1-1, and j1-2 terminals, the diode will work as "reverse emf protection", and can help drain off the power stored in the motor windings when the mosfet is switched off. I see the MOSFET your using has a built in diode, but I would still put one across the motor terminals.

2). Play with the value of R1. R1 is used as a pull-up resistor, it holds the gate of your n-channle mosfet HI (OFF), It maynot be holding it high enough, try 500ohm.

[Alexandr0s]

Thanks, will try that .

[Alexandr0s]

2). Play with the value of R1. R1 is used as a pull-up resistor, it holds the gate of your n-channle mosfet HI (OFF), It maynot be holding it high enough, try 500ohm.

Quick question, I only have 1K ohm resistors lying around at the moment. If I'm correct, I can get 500 ohm resistance by replacing the 1K with two 1K resistors wired parallel right?

[Schmidtc89]

Two 1k Ω resistors in parallel will give you a 500 Ω. (1/1000 + 1/1000)^-1 = 500 Ω

[Alexandr0s]

Thanks .

[jalyst]

• high PWM frequency on the other hand, interferes with rpm readings as the fans internal rpm reading circuit is switched on and off at the PWM frequency, thus the rpm output is switched at the PWM frequency too. this interferes with the regular rpm pulses resulting in erratic rpm readings. this problem is primarily at lower rpm!

I see thanks, hopefully this will be corrected with newer revisions of the PWM spec.

<SNIP> of course, all this problems are related to 3-pin fans only. bus as the PWM versions of gt's are not available till now i will focus on 3-pin fans.

anyway, my controller will definitely be able to use PWM control on 4-pin (real PWM) fans also.

Glad to hear your controller will be dual-mode (PWM/LVC)!
If you pull-off some clever PCB design, then I'd be keen to have a go at putting it all together myself, using your schematics.
Unless your plan is to build/sell the end product yourself, which I'd still be interested in!!
Do you think what you have in mind will satisfy everything I'm looking for? (read from there & my subsequent posts)

Thanks again.

[Alexandr0s]

2). Play with the value of R1. R1 is used as a pull-up resistor, it holds the gate of your n-channle mosfet HI (OFF), It maynot be holding it high enough, try 500ohm.

Great advice! I soldered another 1k resistor parallel to the first one (to get 500 ohm resistance), and the Mosfet is barely getting hot at all, even though I'm currently contolling 2 fans with it .

Another quick question: You said something about putting a diode between the j1-1 and j1-2 terminals. Which direction should the diode be facing?

Also, a friend of mine gave me the advice to play with the capacity of the elco to allow for a better control? Is this true, and if so, would a 47uF elco be a good choice?

[fgw]

Another quick question: You said something about putting a diode between the j1-1 and j1-2 terminals. Which direction should the diode be facing?

• kathode needs to be connected to J1-2 (the positive (red) fan wire)
• anode needs to be connected to J1-1 (the negative (black) fan wire)

Also, a friend of mine gave me the advice to play with the capacity of the elco to allow for a better control? Is this true, and if so, would a 47uF elco be a good choice?

47uF is a good starting point, but try various values. you might need to go even below 47uF. the value needs to be adjusted to the load (fan current). expect different fans to require different values.

[CrazyNutz]

Great advice! I soldered another 1k resistor parallel to the first one (to get 500 ohm resistance), and the Mosfet is barely getting hot at all, even though I'm currently contolling 2 fans with it .

Another quick question: You said something about putting a diode between the j1-1 and j1-2 terminals. Which direction should the diode be facing?

Also, a friend of mine gave me the advice to play with the capacity of the elco to allow for a better control? Is this true, and if so, would a 47uF elco be a good choice?

Right on, No Problem

Look at the source schem, the diode across the motor terminals, this is the direction it should be placed
http://pcbheaven.com/circuitpages/PW...r_using_a_555/

As for the cap, yes your friend may be right, it would depend on your switching frequency though(and load like fgw said). If the cap value is too high it can regulate the voltage that your fan see's to a higher degree, i.e. you may not be able to have much range in the lower RPM region (you may not even be able to reach low rpm). So yes try it lower. Also If you go too low you may start to hear the PWM switching which will drive you nutz..

[Alexandr0s]

Thanks for the tips guys. I will get some new parts next week. Most importantly I'll get rid of those horrible SMD's. Fun when you have a good pcb and some soldering skills, not so fun when working with a perfboard .

Would it also be useful to try out different values of the potentiometer?

[Alexandr0s]

Anyone able to answer my last question regarding the potentiometer?

[fgw]

Anyone able to answer my last question regarding the potentiometer?

although the creator of this circuit used the NE555 a little bit different than the datasheet suggests for PWM operation, the formula to calculate the PWM base frequency should still be valid. but it looks like its working, so who cares.

anyway, changing either C3 or R2 will change PWM base frequency.

in your circuit this should result in 1440Hz:

f = 1,44 / (R2 * C3) = 1,44 / (100.000 * 0,00000001) = 1.440Hz

you can go lower on either R2 or C3 to increase PWM base frequency. the datasheet suggests to use a value larger than 1nF for C3. taking this into account, i would recommend the following values for some example frequencies:

PWW freqency=6kHz C3=12nF R2=20k
PWW freqency=12kHz C3=12nF R2=10k
PWW freqency=21kHz C3=6.8nF R2=10k