Home made fan controller

[deadlysyn]

So I am looking for a way to make a fan controller that would automatically adjust fan speeds depending on temperatures. I had this idea the other day, because I am working on putting together a water cooling loop, and I don't really trust Speedfan to do it, and would rather just build something. I was looking at the guide above to make my own PWM fan controller, and thought to myself, instead of the Rheo, why not find a way to have it adjust automatically. If there is a way that I can solder some parts in that would allow me to set a temperature where the fan speed changes, even if by jumpers or changing out a resistor, diode, or whatever it might be, I would love to hear it. Chances are for the temp sensor, I will be using THIS (http://www.jab-tech.com/Bitspower-Silver-shining-G-1-4-Temperature-Sensor-Stop-Fitting-BP-WTP-CT-pr-4345.html). This will be controlling 3 120mm fans, which i would prefer to each have their own circuit. If there was a way that I could have it pass data on to the computer as well, that would be something interesting to add, but I don't know the first thing about writing any programs.

[deadlysyn]

Bump. Any electronics engineers have an idea or maybe even point me in the right direction. I'm up for some reading as well.

[Moto7451]

Thermistors will change in resistance based on the temp. You could use one of those (plus possibly some other circuitry) to change the output of the PWM.

[Brutal-Force]

There is more to it then just a thermistor, that would only turn the fan on and off depending on what your using. They will not control the fans speed though. They use resistance to ground and that value is then given to a module with a set parameter which controls the amount of voltage to the fan.

Using a Thermistor you would have as an example: Temperature = 50 degrees, Resistance value 35 Mega Ohms. Tempure = 100 degrees Resistance = 500 Ohms and so on. So it would be a variable resistor, but the amount of current you could send through it would be limited. I am speaking from an Automotive Application where such a resistor may be 12V but more likely 5V. When you try and pull 40Amps through that circuit you will in all likely hood kill that Thermistor. Additionally the one I am referring to is an Automotive Temperature Sensor, I can't imagine a smaller one being able to do what you want without it using a control module.

What you need is two circuits, where the Thermistor is the control circuit with maybe a 2 or 3V reference signal to a control module to turn on your fans. Where would you install this anyways? under the HSF? or just ambient case temp?

I would think it would be easier to just use the CPU Fan output as the control to a fan controller. Set the fan controller or Pumps or whatever on high and done.

[deadlysyn]

There is more to it then just a thermistor, that would only turn the fan on and off depending on what your using. They will not control the fans speed though. They use resistance to ground and that value is then given to a module with a set parameter which controls the amount of voltage to the fan.

Using a Thermistor you would have as an example: Temperature = 50 degrees, Resistance value 35 Mega Ohms. Tempure = 100 degrees Resistance = 500 Ohms and so on. So it would be a variable resistor, but the amount of current you could send through it would be limited. I am speaking from an Automotive Application where such a resistor may be 12V but more likely 5V. When you try and pull 40Amps through that circuit you will in all likely hood kill that Thermistor. Additionally the one I am referring to is an Automotive Temperature Sensor, I can't imagine a smaller one being able to do what you want without it using a control module.

What you need is two circuits, where the Thermistor is the control circuit with maybe a 2 or 3V reference signal to a control module to turn on your fans. Where would you install this anyways? under the HSF? or just ambient case temp?

I would think it would be easier to just use the CPU Fan output as the control to a fan controller. Set the fan controller or Pumps or whatever on high and done.

The way this would be set up would be a temperature sensor in the water loop, which will be hooked up to the controller and would hopefully be controlling fan speeds based on the temp of the water in the loop. I want to set it up so that, for instance, if the water was 60C, that it ramps the fans up to 100%, but if the temp is lower than the preset, to run at about 58% (about the equivalent of 7 volts) of the rated speed via PWM (which pulses 12 volts to the fan instead of lowering voltage). The reason I want to do PWM, is due to the fact that they lose torque at lower voltages, which decreases airflow, but running 12 volts in short bursts to get the fan speed you want will keep the torque and airflow, with less noise. This information is based off the fan mods sticky up above.

[Brutal-Force]

Hrm, well being that you are talking about a W/C loop. It is very similar to a Car. They sell Thermistors (Coolant Temperature Sensors) that are designed operate under variable resistance. When you input 5V or 12V to them, they return that voltage to the Control module, which in turn turns on the fan. You could probably use the same sensor. Normally on a car, the differences in temp. determine the injection Pulse Width of the injectors so they get more fuel when the car is colder. In your case the Pulse width could be used for the fans. The trick is the circuitry inside the control module, thats where it gets complicated. You could however build a set of transistors that open at different Voltage thresholds. So that as the temperature increases, the resistance decreases and the voltage increases. As a matter of fact, if your only running 5-12V to your Fans, a temperature sensor "might" withstand the amperage. Dunno, I have never tried something like that. If it does, then Your fan speed would vary depending on the resistance in the sensor. On the low side, it wouldn't matter because most 80-120mm fans have a low voltage threshold, so more or less it would just cut off. But on the high end, if your PSU is only putting out 12V then that should be the high. Just a thought. If that worked, you could tap a hold in your resevoir and just use the temp sensor, only problem would be you might need one for each fan depending on the load it can hold. Most temp sensors for cars are not expensive, so I would give it a go. As a matter of fact, I have a couple at work. I might just try and do some tests.

On a side note: This will probably work in a practical sense, but if it does, for the temps your talking about on a WC setup You would need a lot finer Thermistor. On a car the temps vary between (actually below freezing) 20 degrees up to 250 F degrees or higher.

Another way might be to just get... say 3 or 4 different thermistors, each designed to operate at a different temperature (on/off switches if you will.)
You could then switch each to a transistor on say a 2 or 3V circuit to the base of the transistor. Then have each of the 4 transistors running different voltages to the Collector and then run the emitter through a surge capacitor? on to the fans. I would imagine a capacitor could handle a single fan. If not, then only use 3v on each of the collectors, but run each of the emitters to a relay and then have each relay leg using 6, 8, 10, 12V. this would give you the option of variable speed, but not with PWM.

[deadlysyn]

I think I may need to clarify what I am actually wanting to do here. For starters, here is the guide to the fan controller:
http://www.overclockers.com/forums/showpost.php?p=4253267&postcount=2
Here is a link to the thermal sensor I am looking at:
http://www.jab-tech.com/Bitspower-Silver-shining-G-1-4-Temperature-Sensor-Stop-Fitting-BP-WTP-CT-pr-4345.html

I was hoping there was a way that I could build a circuit that replaces the rheostat on that controller, which would send a signal that adjusts the fan speed based on the temperature from that particular sensor. I hope this makes a little more sense.:beer:

[Brutal-Force]

http://lh4.ggpht.com/_LM3ymtCqxvw/S0LpvcOIOeI/AAAAAAAAAWE/JHC2kuArMxw/temperature-controlled-fan-12v-dc.GIF

Although I think in the end you might just be doing a whole lot of work for nothing.

You can buy a PWM fan pretty inexpensive. Then just attach a variable resistor/thermistor in place of the rheostat. It really is the cheapest/fastest/most efficient way.

[Brutal-Force]

For Example, this fan. (http://www.frozencpu.com/products/7241/fan-432/Arctic_Cooling_Arctic_Fan_12_PWM_120mm_x_385mm_Fan _ACF12PWM.html?tl=g36c15s69&id=ZJyNxXVS)

And this (http://www.coleparmer.com/catalog/product_view.asp?sku=0843200)

Or use that thermistor and where you put a rheostat on Skieth's Controller, wire in that Thermistor instead. Run it to your radiator, (resevoir would work, but since its your radiator your cooling, you should epoxy it there or just before there in a coolant line.

P.S. The Rheostat is the 10K Ohm Potentiometer. I also missed the This Sensor in your original post. I don't know if that one would work. Essentially, Skeith designed that controller with a 10K Ohm Potentiometer. Basically it would allow you to probably dial in from 1000 (1K Ohm) - 10,000 (10K) Ohms.
So basically whatever sensor you use has to do the same with the Highest temp you want it to operate at the 1000 (1K Ohm) and the Lowest 10,000 (10K Ohm). You can test this by dropping it pot of water on the stove and slowly warming it up. The Higher resistance slows your fan down, the lower resistance is max speed.

I hope I helped. :/

[deadlysyn]

http://lh4.ggpht.com/_LM3ymtCqxvw/S0LpvcOIOeI/AAAAAAAAAWE/JHC2kuArMxw/temperature-controlled-fan-12v-dc.GIF

Although I think in the end you might just be doing a whole lot of work for nothing.

You can buy a PWM fan pretty inexpensive. Then just attach a variable resistor/thermistor in place of the rheostat. It really is the cheapest/fastest/most efficient way.

This will be set up on my radiator, which will be controlling 3 fans. I thought about doing one that just adjusted voltage based on temperatures, but I have read that PWM is better for the longevity of the fans. Also, according to my reading, running fans at less than their rated voltage decreases their torque, which in turn decreases pressure. When it comes to WC, the more pressure the better. Once I have a chance, I will take a look at the diagram posted, and see if it will do what I am looking for.

[s.t.a.t.i.c]

i am looking for a circuit with the same requirements as well.

looking at the diagram u posted with pwm output, can't you just wire the sensor(or thermistor)
between the +12V and the rheostat?

i am currently making the pcb for that schematic but i don't have a sensor to try it with.

[Brutal-Force]

What you say is true regarding PWM, thats why I went back and looked at the Controller Skieth drew up. It will do what you want. You just need to swap out the actualy rheostat with a 10K Ohm Thermistor.

[King107s]

So I am looking for a way to make a fan controller that would automatically adjust fan speeds depending on temperatures. I had this idea the other day, because I am working on putting together a water cooling loop, and I don't really trust Speedfan to do it, and would rather just build something. I was looking at the guide above to make my own PWM fan controller, and thought to myself, instead of the Rheo, why not find a way to have it adjust automatically. If there is a way that I can solder some parts in that would allow me to set a temperature where the fan speed changes, even if by jumpers or changing out a resistor, diode, or whatever it might be, I would love to hear it. Chances are for the temp sensor, I will be using THIS (http://www.jab-tech.com/Bitspower-Silver-shining-G-1-4-Temperature-Sensor-Stop-Fitting-BP-WTP-CT-pr-4345.html). This will be controlling 3 120mm fans, which i would prefer to each have their own circuit. If there was a way that I could have it pass data on to the computer as well, that would be something interesting to add, but I don't know the first thing about writing any programs.

I used a pulse width modulation fan and spliced into a 4-pin header with some longer wire and hooked it up the Main board's pin-out for the CPU and it works like a charm!


My 120mm PWM fan is in a push configuration with a BIX 120mm radiator. I could let the mainboard do the work for the PWD settings but I chose to use the gigabyte MB software and have set temperature ranges with corresponding fan speeds. i.e. set fan to minimum of 50% then start to ramp fan speed from 25C to 100% at 40C. It works quite well and does not require any external controlers or temperature sensors.

The mainboard pinout will carry 1amp for most boards which is more than enough for 1 fan. If you need to run a lot of fans or very powerful fans connect the power line to a regular positive rail from a spare molex and the ground. The PWM and sensor lines need to stay though.

Let me know if you need more help, and ill try to post pics when I get home.

Edit: http://www.overclockers.com/forums/showthread.php?t=612078 I brought this subject up a long time ago

[deadlysyn]

I used a pulse width modulation fan and spliced into a 4-pin header with some longer wire and hooked it up the Main board's pin-out for the CPU and it works like a charm!


My 120mm PWM fan is in a push configuration with a BIX 120mm radiator. I could let the mainboard do the work for the PWD settings but I chose to use the gigabyte MB software and have set temperature ranges with corresponding fan speeds. i.e. set fan to minimum of 50% then start to ramp fan speed from 25C to 100% at 40C. It works quite well and does not require any external controlers or temperature sensors.

The mainboard pinout will carry 1amp for most boards which is more than enough for 1 fan. If you need to run a lot of fans or very powerful fans connect the power line to a regular positive rail from a spare molex and the ground. The PWM and sensor lines need to stay though.

Let me know if you need more help, and ill try to post pics when I get home.

Edit: http://www.overclockers.com/forums/showthread.php?t=612078 I brought this subject up a long time ago

I will be running a triple rad, which has 3 fans, and the fans I have are only 3 pin (12v+, GND, and RPM). The probe thermistor that was previously linked will not work in this situation, since it is too long for the res, and can not be installed into the rad without destroying it. I am simply looking for a circuit that will replace the rheostat mentioned in skeith's guide. Instead of being variable, like a rheo, I want something that would run the fans at 100% if temp is higher than a preset temp, and at 60% if lower than the preset temp. Basically I want the whole thing automated, so that I don't have to interact with it, unless the controller fails.

[deadlysyn]

So after doing some looking around, I was able to find this:
http://images.bit-tech.net/content_images/2001/12/pwm_fan_controller/2.jpg
It looks like it is virtually the same thing as BF has been trying to explain. So at this point, how would I go about setting the temperature that I want the fans to ramp up at. If I wanted them to go full speed at 50°C, would it be a change in a resistor somewhere, or do I need a specific thermistor?

[Brutal-Force]

Either actually. Finding the right resistor might be difficult though, since we are talking about temperatures where your fans should come on at say... 60, ramp up to 90 full blast but shut off after 50. But choosing the right thermistor would get you closer. More or less you could just trial and error. Find a Temp. sensor that is 10Kohms at ambient, and warm it up by about 30 degrees, it shouldn't drop to under 1K ohm.

[deadlysyn]

I had shot out a PM to someone earlier today about this, since they are posting in threads like this one quite regularly. A couple of points were brought up, which I will address here as well. One of them, is that I could be spending hours at a time on trial and error, trying to get the temperature to fan speed at the balance I want. Another being that some fans have a tendency to make some noise when controlled via PWM. There is also the idea that fans don't lose any power or torque when they are undervolted, but will work exactly the same whether controlled via PWM or voltage adjustments. I was also thinking about leaving an option to add a display to monitor fan speeds, which can not be monitored if the fan controlled with this type of controller. Because of these things that I have not thought of previously, I am reconsidering this controller build, and thinking about doing a linear type of controller, which may still allow the monitoring of fan speeds.

[Brutal-Force]

Well, I was going to say, undervolting only loses the amount of torque your undervolting, but just because you PWM does not mean it will give you more torque.

As far as trial and error goes, thats only if you don't know the exact numbers/components your dealing with. Your going to fabricate with what you have... that way you save money.

One way to "fine tune" is to just install a 1k or 10k rheostat inline with your thermistor.

On the note of thermistors. I have a 20 degree thermistor at work you can have I tested it from 1K Ohm (Ambient 20 degrees) - 10 Ohms (60 degrees Celcius). You can build your module based off of that. If I come across a 10K Ohm thermistor, I will let you know. This thing has like a 7/8ths thread on it. and would have to be screwed in about 1". I could probably modify something though you could put inline of the radiator with 1/2" fittings.

[Brutal-Force]

http://lh3.ggpht.com/_LM3ymtCqxvw/S0QnSF--6cI/AAAAAAAAAXs/3JKTDl6oYW8/2010-01-06%2000.58.47.jpg

http://lh4.ggpht.com/_LM3ymtCqxvw/S0QnSZWaEZI/AAAAAAAAAXw/CuKV-EbCB74/2010-01-06%2000.59.08.jpg

Sorry, typo, not 20 degrees, 120 degrees. This should handle a 12V current @30A so you could run directly through it.

And those are 1/2" Compression Fittings.

Sorry about the crappy cellphone pics. I am at work.

[deadlysyn]

Sorry, typo, not 20 degrees, 120 degrees. This should handle a 12V current @30A so you could run directly through it.

And those are 1/2" Compression Fittings.

Sorry about the crappy cellphone pics. I am at work.

That actually looks like it may be something that would do the trick, although I don't know much when it comes to making my own electronics. Are those compression fittings suited to 1/2" ID 3/4" OD tubing? I am also wondering how much restriction this would introduce into my loop. That is the primary reason I was looking for something small, that I could fit into my res. Once the temps equalize in the loop, it wouldn't matter where the thermistor is, since the temps will be the same at any 2 points in the loop. Atleast that is what I gather from my reading in quite a few guides and in the water cooling section.

Feel free to shoot me a PM regarding that thermistor when you have a chance.

Edit: How would the guage of wire soldered to the terminals affect the resistance? I have some wires about maybe 20GA that I was thinking about running for this, since it is small, and very easy to work with, for wire management. The fans I will be using are just medium speed Yates, I think at around 0.4A each.

[Brutal-Force]

I actually went through and found 3 different thermistors after I took those pictures, one is a little smaller and one is alot smaller, the much smaller one is 2M Ohms, and the one that is a little smaller is like the big one 1M Ohm. The difference is that I am sure the much bigger one can handle more amperage and could probably run 3 fans w/o other circuitry involved.

You could use the same guage wire as existing fans, you would just need a larger spade connector. I could probably rummage up something for that. At 0.4A each I dont see why you couldnt run 6 fans off this sensor. It is designed to handle 6-24 volt systems. And I believe it can handle 20-30A.

[deadlysyn]

Everything in this circuit will be soldered, so there is no need for any spade connectors. I am almost sure that I will be doing something similar to the cuircuit that I had posted above, but instead of the PWM, I may be doing the more linear type to keep RPM monitoring. I will check with the person I have contacted about this circuit, and see what he thinks as well, since he as subscribed to this thread, but doesn't really have time to contribute fully to the discussion. Do these have a lower resistance at higher temps, or the other way around? It seems the lower resistance should be at the higher temps, which would speed the fans up when it is more needed. I am still trying to understand the way thermistors work, and could really use some laymans terms.:p

[Brutal-Force]

Yes, lower resistance at higher temps. At ambient temps of around 20 degrees celcius, the Sensor shows a resistance of ~1000 Ohms, or 1M Ohm. As the temperature increases, the resistance decreases. This one will register up to 120 degrees Celcius, so a little above boiling point. At that temperature, the resistance will be about 10 Ohms. These are just rough estimates. I didn't have a stove or anything I could slowly heat water too, and I would have to set up a pot of water with a thermometer in it to register and write down at what temperature/resistance is. Once you graph that out, you will know exactly how much resistance and at what temp. From there you will determinte the amount of resistance needed to turn your fan at the desired speed.

Its actually a fun little project, and with the trial and error, you learn something about Ohms law. Once you master this little experiment, it will make building mods like this a lot easier. Ohms law is the bread and butter for electrical engineering.

You will also notice the lower the resistance, the higher the amperage as long as the voltage is constant. So the Fan will spin faster because it can pull more amps.


Think of it like water flowing (current) through a turbine at a damn, the bigger the opening (Less resistance) the faster it can turn the turbine. Same concept.

Study this... it will help. http://en.wikipedia.org/wiki/Ohm%27s_law

[deadlysyn]

Yes, lower resistance at higher temps. At ambient temps of around 20 degrees celcius, the Sensor shows a resistance of ~1000 Ohms, or 1M Ohm. As the temperature increases, the resistance decreases. This one will register up to 120 degrees Celcius, so a little above boiling point. At that temperature, the resistance will be about 10 Ohms. These are just rough estimates. I didn't have a stove or anything I could slowly heat water too, and I would have to set up a pot of water with a thermometer in it to register and write down at what temperature/resistance is. Once you graph that out, you will know exactly how much resistance and at what temp. From there you will determinte the amount of resistance needed to turn your fan at the desired speed.

Its actually a fun little project, and with the trial and error, you learn something about Ohms law. Once you master this little experiment, it will make building mods like this a lot easier. Ohms law is the bread and butter for electrical engineering.

So if I wanted my fans to run at 100% of their rated speed when the temps got to 55C, I would need to find a way to get it to 0 resistance between the fan and the thermistor, if I'm not mistaken.

Just taking a wild guess at the resistance calculation, the variance is 990 Ohms over 100C. This makes my figure of 55 out to be 35 degrees over ambient. If I am doing the math correctly, this would set it to about 643.5 Ohms, at 55C. There may be a huge flaw in my math, and I pretty much did it like the resistance change was linear as the temps changed. Am I doing the math correctly, or is there something I don't know about calculating the resistance just based off knowing the numbers?

[noxqzs]

I haven't read all posts in detail, so if its already been mentioned I apologize, but you could also use a LM35 (http://www.national.com/mpf/LM/LM35.html#Overview) temperature sensor, which has a linear output of 10mV/degree. Couple that with an inexpensive arduino or similar microcontroller that could act as a PWM source. This would allow you to really fine tune the range of temperatures. You can buy hobby kits for cheap money, and it can be interfaced with USB/rs232 as well.

[Brutal-Force]

I looked up the Arduino, and yes... it looks like he might be able to use that. Unfortunately, deadlysyn has yet to mention what kind of budget he has in building this contraption. There are actually many options he could take, I guess he just needs to decide where he wants to start.

[noxqzs]

So after doing some looking around, I was able to find this:
http://images.bit-tech.net/content_images/2001/12/pwm_fan_controller/2.jpg
It looks like it is virtually the same thing as BF has been trying to explain. So at this point, how would I go about setting the temperature that I want the fans to ramp up at. If I wanted them to go full speed at 50°C, would it be a change in a resistor somewhere, or do I need a specific thermistor?

I took a peek at the diagram, specifically the MIC502. After reading the datasheet (http://www.micrel.com/_PDF/mic502.pdf), on page 12 there is an explanation for the resistor selection. In your diagram, you would remove the variable potentiometer, and put another resistor in parallel with the thermistor. These would be connected in series with R2. Pin 1 would be connected to the node between R1/thermistor and R2. The value of this new resistor and R2 of you diagram would represent the voltage divider of the circuit. Initially you could use a potentiometer to dial in the fan speed of your choice, remove it and replace with a fixed resistor of similar value. The type of thermistor will be dependant on the resistances you choose.

[deadlysyn]

Budget is a bit of an issue. I would like to keep this as cheap as possible. I have found a Scythe controller that does the same thing, but I think it goes off air temperature instead of water.

As far as what temperature relates to what speed, I would like it to ramp the fans up to 100% at 55C. Below 55, I was hoping to have the fans running at 60%. I am also thinking about moving away from the PWM idea, because I am thinking I may want to keep speed monitoring of the fans. I have been looking for the MIC502, and haven't had much luck (only tried mouser.com for now).

I would really like to build this, rather than just buy something, partly for the possible money savings, but mostly for the experience. I have been thinking about getting more into electronics, and I figured this would be a good way to get started.

[Brutal-Force]

Your best bet is to buy what you "need". Then get stuff together to mimic what you have. The original controller is actually sound. You only need to swap a thermistor in place of a potentiometer.

Definition Potentiometer - A user-adjustable variable resistor .
Definition Thermistor-A thermistor is a type of resistor whose resistance varies with temperature.

[noxqzs]

MIC502 DigiKey $2.25 (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=576-1241-ND)

Different manufacturers sometimes have slightly different codes. I am placing a big order tomorrow for parts I need at work, and will order one to play around with. I will try to build a circuit with the parameters you need.

[Brutal-Force]

So if I wanted my fans to run at 100% of their rated speed when the temps got to 55C, I would need to find a way to get it to 0 resistance between the fan and the thermistor, if I'm not mistaken.

Just taking a wild guess at the resistance calculation, the variance is 990 Ohms over 100C. This makes my figure of 55 out to be 35 degrees over ambient. If I am doing the math correctly, this would set it to about 643.5 Ohms, at 55C. There may be a huge flaw in my math, and I pretty much did it like the resistance change was linear as the temps changed. Am I doing the math correctly, or is there something I don't know about calculating the resistance just based off knowing the numbers?

Yes, if you wanted your fans to run at or near 100% you would try to reduce the resistance to zero, but zero is relative. A difference of 1 ohm and 100 ohms is negligibe, but the difference of 1000 Ohms (1K Ohm) and 10K Ohms is a big difference.

If for example you added a User defined potentiometer in the same circuit, you could vary the fan speed based off the temperature/resistance. By having a Potentiometer, you can add to the resistance in Thermistor Circuit. So in essence, by adding a 1k Potentiometer, you could have up to 2K Ohms in the circuit, which would make your fan circuit switch instead of 0.001 Ohm - 1000 Ohms, be 1000 (1K)-2000 (2K) Instead, You don't really have to go from 0 as 0 would be full amperage on your fan. Depending on what your power supply gives in amperage, you would kill your fan quickly. If its only rated at 0.4A and lets just say the fan circuit is rated at 10A, you would have to put a resistor in to drop the Amps to 9.5Amps at 12V. That would be about 30 Ohms in the circuit to drop to just 0.4A. So then you want to vary from say 0.1A-0.4A. So say 30/40/60 Ohms. Would be your fan speeds.

I=V/R 0.2= 12/60
0.3= 12/40
0.4= 12/30

If you had 40 Amps at that circuit. You would have to step down Alot.


R=V/I 1.2Ohms = 12V/10A

As you decrease the Resistance, you increase the Amperage, which you don't really want in this case. Unless your fans are rated this high. So In essence what you want to do is drop your Amperage down with a larger resistor.

1.2A = 12V/10Ohms
0.6A = 12V/20Ohms

Its all a numbers game, Look up ohms law and do some experiments.

[deadlysyn]

I was mistaken about the controller I had found being a Scythe. It is actually the NZXT Sentry 2 (http://www.performance-pcs.com/catalog/index.php?main_page=product_info&cPath=52_87_137&products_id=26057). I had thought about this one, but I am unsure about the 10 watts per channel. While that gives me up to 1.2A per fan (unless I did my math wrong), if I had decided that I wanted to put some Delta or Panaflo screamers on the rad, there is a chance I could easily kill that controller. It shouldn't be too hard to replace the temp sensor with the one in my OP, but since I would be living with the idea that I didn't build it myself, I would kind of be disappointed in the fact that I started the research and didn't finish the project.

Anyway, BF, it kind of sounds like what you are recommending is putting the thermistor inline with the fans power lines, with a resistor if needed to regulate the fan speeds depending on temperature. Is this a correct assumption, or is there more to what you are saying that I am missing?

MIC502 DigiKey $2.25 (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=576-1241-ND)

Different manufacturers sometimes have slightly different codes. I am placing a big order tomorrow for parts I need at work, and will order one to play around with. I will try to build a circuit with the parameters you need.

Thanks for the link. I had really only had time to check mouser.com, and they didn't seem to have one in stock. They seemed to have quite a bit of everything else, but I was having a hard time understanding which thermistor to get. I am also having the same troubles figuring out what resistors I need, since I don't really know where to start with the calculations. I was hoping for 60% fan speed below 50C, and 100% above 50C. I also need the thermistor to be able to be submersed in water, but still need it to be compact in a way. If there happens to be something in a stop fitting style with G1/4" (1/4" BSPP) threads, just like the temp sensor in my OP (will dig up the link again as well), it would be perfect for what I am hoping to do.

Edit: Here is the fitting with temp sensor: http://www.jab-tech.com/Bitspower-Silver-shining-G-1-4-Temperature-Sensor-Stop-Fitting-BP-WTP-CT-pr-4345.html.

[Brutal-Force]

Yes put temp sensor in line with fan controller. It will just add more resistance. Just find the right thermistor something that is about 10kohms maybe.

[deadlysyn]

So if I'm getting this right, the fan speed won't be constant, as long as temps are changing? It sounds like using this method sounds like the change in fan speed would be more gradual rather than hitting a set temp and then ramping up from partial to full speed. I'm going to look into this some more, as it sounds like it could work well for what I'm going to do.

[Brutal-Force]

Here is what I recommend you do before you get all buildy buildy.

Go to Radio Shack, Pick up a cheap 3 dollar fan, a 10k Ohm Potentiometer (The kind used for radio dials) and a thermistor. Preferably one you can submerse in water.

Hook them up to a small 12Volt battery. in a series Battery Positive ---> Thermistor ---> Poti ----> Fan ---> Back to Negative. Now you can submerse the sensor in water and heat up gradually. If you have a multimeter take note of the resistance in the Sensor while you do this. Also take note of the potentiometer. You can watch the resistance values changing and give you an idea of whats going on. This is the basic principal of what your doing. From there you can build your fan setup.

At this point, you have to start with a prototype since you don't posses the knowledge to just build this from scratch. Have fun with it, you will feel like you accomplished something even if you never build it and decide that it makes more sense financially to just buy something and modify it, then it does to build it from scratch. You will also respect more what you have spent your hard earned money on.

[noxqzs]

Hook them up to a small 12Volt battery. in a series Battery Positive ---> Thermistor ---> Poti ----> Fan ---> Back to Negative.

One thing to note when doing this is the power capacity of the components. You wouldn't want a 1/4W thermistor in a circuit that is pushing a 1/2W fan for example.



Regarding your question of fan speed, the fan would ramp up and down based on temperature and would have a HIGH and LOW speed that would be adjustable based on the selection of resistances driving the MIC502. I have run some basic numbers and will show you an example when I have enough time to make it all legible.

[deadlysyn]

Sounds like an interesting project. I actually have a bunch of old 80mm fans laying around that I have taken out of burnt PSU's. Local shops sell garbage PSU's, and when I replace the junk with more reputable parts, I take the fans out, and they sit in a box in my office. I also have an old PCP&C Silencer 310, which I have jumped for priming my water pump. That takes care of the fan and battery, so it seems that I just need to get a thermistor and a potentiometer.

One thing to note when doing this is the power capacity of the components. You wouldn't want a 1/4W thermistor in a circuit that is pushing a 1/2W fan for example.



Regarding your question of fan speed, the fan would ramp up and down based on temperature and would have a HIGH and LOW speed that would be adjustable based on the selection of resistances driving the MIC502. I have run some basic numbers and will show you an example when I have enough time to make it all legible.

Go figure, someone posts while I'm posting. I will keep this in mind when I go pick up the thermistor and pot. Is the resistor or pot inline with the thermistor for that reason?

Anyway, it will be great to see your results. Also, this circuit will hopefully be driving 3 Yate Loon mediums. Did the one you built have the capacity to run around 1.2A?

[noxqzs]

A little update. I received all my supplies today, and got a chance to play around with the chip. It is very easy to setup, and the circuits you posted in the Bittech article, are identical to the ones in the datasheet for the chip. The fan I used to test was limited to low power because I didn't have any npn transistors with enough juice to power a bigger fan. This is a small issue, as I know I have a few 5A ones laying around.


Sorry about the quality of the phone camera, but that is all I had near me.
http://home.comcast.net/~noxqzs/PWMcontroller/MIC502PRJ.jpg


Hopefully I can dig into this during the weekend and maybe even etch a circuit board. Time is tight though. Wedding in two months, and a boatload of tiling and finish carpentry to do. Woman is also planning on starting her oven like yesterday.

[cyberfish]

How about a LM335 to a differential amplifier with a reference voltage set by a rheostat, then amplified to scale from 0 to 12V? The output can go into a NPN to set the fan voltage (which scales with temperature, with a set offset).

Sorry I don't have any circuit drawing program on this computer.

[deadlysyn]

A little update. I received all my supplies today, and got a chance to play around with the chip. It is very easy to setup, and the circuits you posted in the Bittech article, are identical to the ones in the datasheet for the chip. The fan I used to test was limited to low power because I didn't have any npn transistors with enough juice to power a bigger fan. This is a small issue, as I know I have a few 5A ones laying around.


Sorry about the quality of the phone camera, but that is all I had near me.
http://home.comcast.net/~noxqzs/PWMcontroller/MIC502PRJ.jpg


Hopefully I can dig into this during the weekend and maybe even etch a circuit board. Time is tight though. Wedding in two months, and a boatload of tiling and finish carpentry to do. Woman is also planning on starting her oven like yesterday.

When you have a chance, could I talk you into a close up of the circuit? Do you think it would be hard to build it to handle my 3 Yates? Happy to see some results with it.

How about a LM335 to a differential amplifier with a reference voltage set by a rheostat, then amplified to scale from 0 to 12V? The output can go into a NPN to set the fan voltage (which scales with temperature, with a set offset).

Sorry I don't have any circuit drawing program on this computer.

If you happen to come across a circuit drawing for this, I would love to see it as well. I am considering quite a few options for the controller. In the meantime, I have just bought a Rheobus to control the fans, but it will only be temporary. I still want to build something that automatically controls the fan speed based on the water temperature.

[cyberfish]

No idea if this will actually work :).

(I am a second year electrical/computer engineering student)

Using a microcontroller will be the best, but they require more supporting circuitry.

[noxqzs]

HERE (http://home.comcast.net/~noxqzs/PWMcontroller/DSC_0753.JPG) is a link to the full size pic of the mockup. The top left variable potentiometer regulates 0-100% output with a 13Kohm-50Kohm range. (A thermistor with a 10-100k resistance in your temp range would would be a good candidate) The bottom left variable is set at 33Kohm, and can be used to adjust minimum speed of fan. The top right variable is used between the npn transistor and the MIC502 output. Its value is 270ohm and can be replaced with a fixed resistor. The circuit could still benefit from some smoothing capacitors here and there, but it does work.

As far as powering fans, you are limited by the transistor used at the output. As an example, I used a TIP122 from Fairchild Semiconductor. It is rated at 5amps continuous.

http://home.comcast.net/~noxqzs/PWMcontroller/mockup.jpg



It had no problem powering 3 of my delta fans. Without active cooling, the transistor does get a little hot (50-70*C), but that is well withing its operating temp. In addition its suggested to have a small heatsink on it, which I didn't put on. The breeze from the 3 fans in the picture, was enough to keep it at 30*C.

Here are some shots with 25%, 50%, 75%, and 100% duty cycle output(duty cycle output is the percent of time a signal is ON at any frequency.)

http://home.comcast.net/~noxqzs/PWMcontroller/25pduty.jpg

http://home.comcast.net/~noxqzs/PWMcontroller/50pduty.jpg

http://home.comcast.net/~noxqzs/PWMcontroller/75pduty.jpg

http://home.comcast.net/~noxqzs/PWMcontroller/100pduty.jpg

The temperature stayed within 15 degrees from room temp at full power with 3 fans blowing on the transistor. Without any cooling , the temp shot up to about 70*C in a 20*C room. I also have another candidate to power some fans.

http://home.comcast.net/~noxqzs/PWMcontroller/transistors.jpg

The one on the right, is what I am currently using. It is rated at 5Amps (60Watts). The one on the left is a MJL3281A by ON semiconductor. It is rated at 15A (200Watts)

I will keep messing around with it.

[noxqzs]

How about a LM335 to a differential amplifier with a reference voltage set by a rheostat, then amplified to scale from 0 to 12V? The output can go into a NPN to set the fan voltage (which scales with temperature, with a set offset).

Sorry I don't have any circuit drawing program on this computer.

I have used the LM335 numerous times and it is a solid idea. The circuit is very simple to make, and definetly cheaper, but the fans might suffer from startup issues with low voltage output at lower temperatures.

[deadlysyn]

HERE (http://home.comcast.net/~noxqzs/PWMcontroller/DSC_0753.JPG) is a link to the full size pic of the mockup. The top left variable potentiometer regulates 0-100% output with a 13Kohm-50Kohm range. (A thermistor with a 10-100k resistance in your temp range would would be a good candidate) The bottom left variable is set at 33Kohm, and can be used to adjust minimum speed of fan. The top right variable is used between the npn transistor and the MIC502 output. Its value is 270ohm and can be replaced with a fixed resistor. The circuit could still benefit from some smoothing capacitors here and there, but it does work.

As far as powering fans, you are limited by the transistor used at the output. As an example, I used a TIP122 from Fairchild Semiconductor. It is rated at 5amps continuous.

http://home.comcast.net/~noxqzs/PWMcontroller/mockup.jpg



It had no problem powering 3 of my delta fans. Without active cooling, the transistor does get a little hot (50-70*C), but that is well withing its operating temp. In addition its suggested to have a small heatsink on it, which I didn't put on. The breeze from the 3 fans in the picture, was enough to keep it at 30*C.

Here are some shots with 25%, 50%, 75%, and 100% duty cycle output(duty cycle output is the percent of time a signal is ON at any frequency.)

http://home.comcast.net/~noxqzs/PWMcontroller/25pduty.jpg

http://home.comcast.net/~noxqzs/PWMcontroller/50pduty.jpg

http://home.comcast.net/~noxqzs/PWMcontroller/75pduty.jpg

http://home.comcast.net/~noxqzs/PWMcontroller/100pduty.jpg

The temperature stayed within 15 degrees from room temp at full power with 3 fans blowing on the transistor. Without any cooling , the temp shot up to about 70*C in a 20*C room. I also have another candidate to power some fans.

http://home.comcast.net/~noxqzs/PWMcontroller/transistors.jpg

The one on the right, is what I am currently using. It is rated at 5Amps (60Watts). The one on the left is a MJL3281A by ON semiconductor. It is rated at 15A (200Watts)

I will keep messing around with it.

Good information here.:thup: Is there any way I can talk you out of a list of parts that you used to make this controller? Also, how hard would it be to add three 3 pin connectors to use with the fans, instead of soldering them to the board?

[cyberfish]

I have used the LM335 numerous times and it is a solid idea. The circuit is very simple to make, and definetly cheaper, but the fans might suffer from startup issues with low voltage output at lower temperatures.

Thanks! I didn't think of that.

I guess PWM is the only way to go for fans.

[noxqzs]

Good information here.:thup: Is there any way I can talk you out of a list of parts that you used to make this controller? Also, how hard would it be to add three 3 pin connectors to use with the fans, instead of soldering them to the board?

MIC502 (http://www.newark.com/jsp/search/productdetail.jsp?id=05C4624&Ntt=MIC502BN)
100K variable potentiometer (2x) (http://www.newark.com/bourns/3299w-1-104lf/cermet-potentiometer/dp/32K7936?in_merch=Popular Potentiometers&in_merch=Popular Products&MER=PPSO_N_P_EverywhereElse_None)
500ohm variable potentiometer (http://www.newark.com/bourns/3296w-1-501lf/cermet-potentiometer/dp/62J1468?in_merch=Popular Potentiometers&in_merch=Popular Products&MER=PPSO_N_P_EverywhereElse_None)
Rectifier diode (http://www.newark.com/fairchild-semiconductor/1n4007/standard-recovery-power-rectifier/dp/18C8923?in_merch=Popular Products&in_merch=Popular Products&MER=PPSO_N_P_EverywhereElse_None)
330uF Capacitor (http://www.newark.com/panasonic/eeufm1e331l/capacitor-radial-25v-330uf-capacitor/dp/04M9019?in_merch=Popular Aluminum Electrolytic Connectors&MER=PPSO_N_P_AlumninumElectrolytic_None)
.1uF Capacitor (http://www.newark.com/kemet/c317c104m5u5ta/ceramic-multilayer-capacitor/dp/94H9294)
NPN transistor 5Amp(60W) (http://www.newark.com/fairchild-semiconductor/tip122/transistor/dp/60K7825)
3 pin Molex connector (http://www.newark.com/molex/26-60-4030/multipole-connector/dp/56H5832?in_merch=New Products&MER=NEWSO_S_C_Molex_Molex)



You could substitute fixed resistors for the variable ones, but you will lose ability to fine adjust range. Also, I haven't received the thermistors yet, but once the range of resistances is known, then a suitable thermistor can be put into the circuit to complement R1. When they arrive, I will give you a link to the one that worked best for me.

[four4875]

I support the suggestion of using a microcontroller.

Get one with A/D inputs, for each temp probe you want to use, pwm D/A output for each channel you want. higher resolution ADCs and DACs will affect how fine you can adjust the speeds to temps.

you'd connect your thermistors to the ADC input with a pull up/pull down resistor network from a regulated reference voltage. you could probably figure out temp to resistance info from the thermistor's datasheet, and use that resistance to choose the resistor to pull the thermistor up or down depending on how you choose to arrange it.

The pwn outputs could be connected to some good sized switcher transistors, but you might need to use another smaller switcher between to drive it, if the UC cant sink or source the current to switch fast enough, the transistor spends more time in a resistive state than fully switched on, so it dissipates the voltage as heat. that's why pwm is so much more efficient than linear regulators, pwm reduces the ammount of time the voltage is flowing, while the linear takes some of the voltage and does something with it, turn it to heat. just look at the current needed for the fans you'll be using, get transistors to handle however many fans will be on each channel and maybe oversize it by 50 or 100% for room for expansion, then make sure the microcontroller's outputs can drive it. if not you'll need some kind of buffer.

after you have the thermistors and pwms set up, you just have to set up the software. it can be as easy the program running a loop checking if input is 1, if yes go here, if no go next. next is check if 2... it keeps counting up till one hits yes, then each yes will have a different goto which would be a line or 2 to set the associated pwm channel's output. you could use any number of fan speeds, depending on how many you want to write, could go in 5 or 10% increments or all the way down to 1 or even less than 1% increments depending on the resolution of the PWM, so you could program a scale that should transition the fan speed pretty well with temp. it might be annoying to hear the fans speeds go into an up-down oscillation from sitting at just the right spot to cool down/heat up again when the heat load stays at a constant. I know it's annoying to hear the speed go from silent to blastin just liek that, if its speed creeped up as the temperature did, it'd be less noticable.

then you can serial or USB interface to the computer, add LCD screens, flash memory for temp logging... do alot with microcontrollers.

If you didnt want to do all that you could put the thermistor resistor network to an op amp, feed that output to the pwm circuit initially talked about and you should be set, use the gain of the op amp to change temp transition range, should be able to get a decent transition.

[deadlysyn]

I just wanted to post up, and let everyone know I didn't forget about this. I have been a little busy. Especially since I have been trying to hunt down a good price on a new front axle for my wifes Honda Passport. I broke it when I decided I wanted to go play around in 4WD in the snow. Needless to say, if you are on ice, and the speedometer says 40, you want to be sure the front end doesn't end up getting traction on something. It was fun til it broke, and now because of it, I may end up broke.:(

[noxqzs]

I have this on my backburner as well DS. Life has me cornered right now, but I do intend to finish this project.

[darkcow]

Hey guys, how is this project coming along? I'm thinking about making my own to control 6 delta fans (about 50 watts). and dunking the thermistor into my reservoir. What I don't understand is what type of thermistor or if I need an extra resistor in parallel with it???

[deadlysyn]

Hey guys, how is this project coming along? I'm thinking about making my own to control 6 delta fans (about 50 watts). and dunking the thermistor into my reservoir. What I don't understand is what type of thermistor or if I need an extra resistor in parallel with it???

Right now, life has been throwing me so many curve balls, that I have had to put it on the back burner. Right now, I have my fans on a Rheobus, and it seems to be doing the job. I will be sure to post up and update this thread when I actually have the time to build my own.

[Brutal-Force]

Check out the link in my sig for my PWM Fan controller. its about as big as a pack of matches. Cost of components is not expensive, assuming you have a soldering Iron, Flux, 0.75mm Solder, tip cleaner, cutters, strippers, stock 22-24 guage wire in different colors, a breadboard to practice on. I did the circuit on both a proto board and also just soldered the components direct to the IC chip. (I would recommend practicing on the breadboard first). It was a fun project that took me about a week, but it works like a charm.

[nightelph]

I was wondering the other day; "Why doesn't OCF have an official fan controller circuit?" Enough questions and ideas have come through this section that someone could post a front-page article for an inexpensive fan-controller project and make it a sticky. If enough interest was generated, someone could fab the pcbs and put together a kit. That may raise some market questions on the forum, but I think theres a lot of room to run with this. Thoughts?

[EarthDog]

Nice idea elph... but I think the ability to buy the 10's of models of already completed fan controllers outweigh the need to have an OCF made one...

Did I misunderstand you?

[NV]

Home made fan controllers have been brought up many, many times. In fact, I've been thinking about bringing the topic up again myself. Because of the popularity of the idea, I would tend to agree it might be pertinent for someone with experience addressing these threads and a good amount of knowledge in the area to compose a front page article on the topic. Personally I'd be very interested in a front page article on fan controller circuits.

The issue of pcbs I think would be more like the way people build each other LN2 pots and that sort of thing, it doesn't necessarily (and probably shouldn't be) an official OCF circuit.

[I.M.O.G.]

Not sure how relevant this is, but it's maybe half the battle:
http://www.overclockers.com/forums/showthread.php?t=641111

[nightelph]

EarthDog; sure theres lots of prebuilt models out there, but half the fun sometimes is making it yourself. I imagine for those of us who already have the tools for soldering, the cost to make a decent one is pretty darn low.

I.M.O.G.; A prime example! I thought it would be a neat idea to have a dedicated [Official] example. But its just an idea.

:) Just trying to enrich the forum. :)

[I.M.O.G.]

Best way to get a dedicated official example is for someone to write it up as a guide for a sticky or the frontpage. If you write it, we will publish.

[nightelph]

I don't think theres an official content editor for this section, but if anyone (Brutal-Force) wants to get on the front page and a sticky to their name, PM me, I can help.