"Active" DC Fan Controller

[ZeTeX]

Hi  ,
I was looking around the web for an "active" fan controller, what "active" means is that the fan doesn't just turn on (FULL POWER) and off (NO POWER) to set the correct temperature, it means that it would control the voltage to the fan, by the temperature, so if the temperature, for example, is at 50C the fan will be at 30% of its power, 60C and 40% of its power for example and so on.
so I didn't find exactly anything like that so I came up with my own, and after testing it a little bit it works great.

The thing about this controller is that it doesn't turn on your fan at 100% and makes a lot of noise, it turns on the fan just enough.
Here is the super simple schematic:

*R2 should be lower value and not 100ohm, something like 10ohm would be suitable.
As you can see, its no more then LM317 that is controlled by the adj pin that is controlled by the NTC + R1 divider, as the temperature the NTC sensing is increased, the voltage at the output increase.
LM334 is for load, so when the output voltage is too low for the fan, LM334 will always draw 5-10mA. or else the voltage will shot up to the maximum input voltage (and that will cause oscillation because the fan will turn on and then the output will go low and then high again and so on).
Anyways, it works great for me when I tested it.

This controller will be useful for a fan on a heatsink, and that's what I designed it for.

At ~25C the output voltage is ~4.1V
At 90~ the output voltage is ~12V
(You can test your NTC resistance at various temperature and then plug in the resistence and calculate the expect output voltage at a rated temp).

Sorry for the bad English, I don't speak native English.

[m98]

Nice design. Cheap, simple and elegant approach to the problem.

[cvanc]

Nice, handy for big audio amps, etc.

A question about the LM334: Doesn't the fan still present some loading to the 317, even at voltages too low for it to spin?  In other words, is the 334 really needed at all?

[ZeTeX]

 

Nice, handy for big audio amps, etc.

A question about the LM334: Doesn't the fan still present some loading to the 317, even at voltages too low for it to spin?  In other words, is the 334 really needed at all?

That's what I thought also, it really depends on the fan, my best advice if somebody wants to build it, is to build it without the LM334 and see if it works for him.
But yes, LM334 might not be needed at all, for my fan who is spinning as low at ~3V I don't need the LM334.

[Jovana81]

Why dont u use simple thermostat, this would act as some waves till it get some balance and constant speed of fan, maybe it's just me, but i preffere on/off

[Refrigerator]

I made something very similar but i used a diode for temperature sensing, check it out https://www.eevblog.com/forum/projects/i-came-up-with-this-temp-controlled-fan-circuit/msg691717/#msg691717

[ZeTeX]

Why dont u use simple thermostat, this would act as some waves till it get some balance and constant speed of fan, maybe it's just me, but i preffere on/off

Well if your fan is louder then a car...
and the thing is with the on\off circuit is that I think they can osciliate, if your "trigger" temp is at 60C and your heatsink gets to 61C, the fan is going to shoot up to 100% till the temp is reduced to 59C but then after a second or so the heatsink gonna get warm again and over and over again, I just dont like the on\off circuit.

I made something very similar but i used a diode for temperature sensing, check it out https://www.eevblog.com/forum/projects/i-came-up-with-this-temp-controlled-fan-circuit/msg691717/#msg691717

thats ok if you dont have a thermistor, but it is still pretty much the on\off schematic..

[batteksystem]

Why dont u use simple thermostat, this would act as some waves till it get some balance and constant speed of fan, maybe it's just me, but i preffere on/off

Well if your fan is louder then a car...
and the thing is with the on\off circuit is that I think they can osciliate, if your "trigger" temp is at 60C and your heatsink gets to 61C, the fan is going to shoot up to 100% till the temp is reduced to 59C but then after a second or so the heatsink gonna get warm again and over and over again, I just dont like the on\off circuit.

Better if using a specific PID controller with a BLDC fan, but expensive.
I made something very similar but i used a diode for temperature sensing, check it out https://www.eevblog.com/forum/projects/i-came-up-with-this-temp-controlled-fan-circuit/msg691717/#msg691717

thats ok if you dont have a thermistor, but it is still pretty much the on\off schematic..

[rmlazzari]

Well if your fan is louder then a car...
and the thing is with the on\off circuit is that I think they can osciliate, if your "trigger" temp is at 60C and your heatsink gets to 61C, the fan is going to shoot up to 100% till the temp is reduced to 59C but then after a second or so the heatsink gonna get warm again and over and over again, I just dont like the on\off circuit.

Hello, this topic seems old but the subject may not be. If so, I apologize.

I found this topic looking for a circuit for a fan controlled by a thermistor, to cool an LM3886. I'm thinking of putting together a scheme similar to this, using LM317, and I was looking for values ​​for Radj. I had reached 3k6 but I will also try with 2k2, according to the circuit's author.

But just to, who knows, help someone who serves the scheme that uses a comparator (like the LM358, for example), the question that batteksystem raised - the fan keeps turning on and off all the time - can be overcome by adding hysteresis to the comparator. So the fan would start to work when the temperature reached, say, 80 ° C but, instead of stopping at 79 ° C, it would continue to work until the chip dropped to, say, 60 ° C. However, during the time it was on, the fan would be at 100% using transistor driving a relay or almost so, using just transistors for its activation. And in that case, it could be using the LM35, linear temperature sensor.

The calculation of the gain resistors and the resistive network for comparison with the output of the non-inverting LM358 is quite complex. However, there are websites that bring a calculator for this, for example, https://www.daycounter.com/Calculators/Comparator-Hysteresis-Calculator.phtml

Well ... thanking the author of the topic, I am available if anyone is going to use the LM35-LM358 scheme. I've tryied that and this realy works.

P.S.: Excuse the english, this is a Google translation.

[poorchava]

I think this makes sense just as an excersise.

Just take a 6pin AVR or PIC and do the thing. Get it programmed from the factory, which is available for even modest volumes. Output pwm and either drive the fan pwm pin or a mosfet and an inductor + diode to make a crude step down regulator.

Do note, that many 12V DC fans will not soon at below 6V or something.

[NiHaoMike]

The "correct" solution is available off the shelf as fan controller chips, they take care of reading temperature sensors (usually thermal diodes or a transistor connected as a diode), generating PWM, and reporting fan speed over I2C.

Why dont u use simple thermostat, this would act as some waves till it get some balance and constant speed of fan, maybe it's just me, but i preffere on/off

If you want the solder joints to eventually fail from thermal cycling so you can sell a new product to your customer, that's exactly what you want.

[David Hess]

I have made fan controllers in the past with just an operational amplifier, output transistor, and temperature sensor.  The supply voltage usually makes an acceptable reference.  With some cleverness it is also possible to do with just a transistor in shunt feedback configuration.