Temperature controlled fan using 555 and opamp

Thread Starter

sabareeshchambayil

Joined Jul 17, 2015
28
I need to make a temperature controlled 12 volt DC fan circuit which turn on at certain temperature ( say 40°C ) and turn off below 40°C ,but at 40°C the speed should be minimum and up on increasing temperature the fan speed should also increase.

ANY BODY HELP.
I already made this circuit but fan runs at high speed all times and it's noicey.

http://www.escol.com.my/Projects/Project-03(Thermostat-1)/Proj-03.html

And by searching I found this

https://forum.allaboutcircuits.com/threads/circuit-to-convert-linear-fan-control-to-switch-mode.122967/
 

Bernard

Joined Aug 7, 2008
5,398
Does fan have just 2 leads ?
Might use 2nd ref. by connecting U1-6 to U2a-5. + input & variable V from thermistor to neg. input. Drive fan with FET. It is late, will continue later.
 

Thread Starter

sabareeshchambayil

Joined Jul 17, 2015
28
Last edited:

Bernard

Joined Aug 7, 2008
5,398
Fan seems good. I like the first ref. PWM Thermal controller. Select a thermistor of 10k to 50k @ 20 deg. C.
I attached my thermistor to a small heat sink of about 2 sq. in. of copper to couple it to ambient air negating self heating from 600 uA current. I would use a N ch. FET to drive the fan. Note that U1A has the same result as using a 555 as a triangle wave gen. R6 will be a pot. Looking at scope display, the position of the green line
moves up & down as R6 is adjusted. If Th1 is in a hot water bath of 40 deg. C , R6 would be adjusted to where blue line just touches the peak of the yellow line ( 8 V ). If the temp. rises the blue line falls & when it goes below the bottom peak of yellow line ( 4 V ) , fan is full on. It may take a few deg. above 40 to first start the fan, but will regulate from then on.
 

Thread Starter

sabareeshchambayil

Joined Jul 17, 2015
28
Fan seems good. I like the first ref. PWM Thermal controller. Select a thermistor of 10k to 50k @ 20 deg. C.
I attached my thermistor to a small heat sink of about 2 sq. in. of copper to couple it to ambient air negating self heating from 600 uA current. I would use a N ch. FET to drive the fan. Note that U1A has the same result as using a 555 as a triangle wave gen. R6 will be a pot. Looking at scope display, the position of the green line
moves up & down as R6 is adjusted. If Th1 is in a hot water bath of 40 deg. C , R6 would be adjusted to where blue line just touches the peak of the yellow line ( 8 V ). If the temp. rises the blue line falls & when it goes below the bottom peak of yellow line ( 4 V ) , fan is full on. It may take a few deg. above 40 to first start the fan, but will regulate from then on.
Which link you are referring.

And

Which is better microcontroller way

Or


Simply some discrete components and OPAMP etc
 

Thread Starter

sabareeshchambayil

Joined Jul 17, 2015
28
I do not do uC's.

OK

I am new to these electronics stuff, can you please give me a circuit diagram of what I need
I am using this for solar inverter setup and it's getting very hot during operation, and the circuit I made (first link) it's working but always at full speed and this make high noise
 

Dodgydave

Joined Jun 22, 2012
8,851
I need to make a temperature controlled 12 volt DC fan circuit which turn on at certain temperature ( say 40°C ) and turn off below 40°C ,but at 40°C the speed should be minimum and up on increasing temperature the fan speed should also increase.

ANY BODY HELP.
I already made this circuit but fan runs at high speed all times and it's noicey.

http://www.escol.com.my/Projects/Project-03(Thermostat-1)/Proj-03.html

And by searching I found this

https://forum.allaboutcircuits.com/threads/circuit-to-convert-linear-fan-control-to-switch-mode.122967/
This circuit uses a relay to put the fan on/off it does not control the speed...
 

wayneh

Joined Sep 9, 2010
16,270
I don't think you need a 555. You could use an op-amp PWM circuit based on comparing the voltage of a triangle wave to a reference. Then you could amplify the LM35 output to create the desired reference voltages needed to change the PWM duty cycle from 0 to 100% over the temperature range you want.

This probably sounds cryptic to you. Take a look here and it may become clearer what I'm talking about with regard to the op-amps.
 

philba

Joined Aug 17, 2017
960
Lots of different ways to accomplish this. Ideally, I would use a cheap little microcontroller (attiny, probably) and a mosfet so I could set the on temp to be higher than the off temp. This is because, turning the fan on and off at the same temperature will lead to some bad behavior when the temp is at the set point. Look up hysteresis. You'd want at least a few degrees of separation.

If a uC is a bad idea, I'd take a look at the TC642. It does linear control which is better from an ambient noise perspective. It comes in both PDIP and SOIC packages and looks pretty easy to use. It also has a nice fan sensing feature that allows you to know if there was a fan failure - a very good idea to protect your solar controller. This could be done in the uC based approach, too. The datasheet has tons of application info. http://www.mouser.com/ds/2/268/21444c-73589.pdf There are tons of fan controllers out there.
 

ArakelTheDragon

Joined Nov 18, 2016
1,327
What you need is a regulator. When the voltage changes from a thermal resistor or preferably an "LM335" sensor, that voltage is fed to the positive end of an LM324 with a negative feedback and you get the voltage you need to control the fan. The speed will rise with the temperature, the problem is that the current from LM324 will be little (mA) and if you need more, you need to put a transistor and the fan in the emitter. Thats the easies way to control a motor (fan or anything else).
 

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philba

Joined Aug 17, 2017
960
I don't think that circuit is terribly practical for our friend. A dual power supply is kind of a pita. If anything, using a 12V wall wart is a much more practical approach, especially with a 12V fan. 5V for the logic can be taken via a cheap 7805 or similar VR. I still think using something like a TC642 is the most straight-forward way to go if a microcontroller isn't in the plan.
 

Dodgydave

Joined Jun 22, 2012
8,851
Yes it's a two speed speed fan control, you can set the upper and lower temperature speeds.

It can be modified using pin 5 of the 555 chip to vary the speed with the temperature.
 

ArakelTheDragon

Joined Nov 18, 2016
1,327
I don't think that circuit is terribly practical for our friend. A dual power supply is kind of a pita. If anything, using a 12V wall wart is a much more practical approach, especially with a 12V fan. 5V for the logic can be taken via a cheap 7805 or similar VR. I still think using something like a TC642 is the most straight-forward way to go if a microcontroller isn't in the plan.
He doesnt needs a dual power supply, he needs "15V" on the "+" power supply and "0V" on the negative power supply. As the temperature increases (10mV per degree) the voltage will increase and if the DC motor is voltage controlled (not PWM) than it will just run.
 

Thread Starter

sabareeshchambayil

Joined Jul 17, 2015
28
Yes it's a two speed speed fan control, you can set the upper and lower temperature speeds.

It can be modified using pin 5 of the 555 chip to vary the speed with the temperature.

Made this circuit but the R5 pot has no effect on the circuit.
Used 4.7 k Thermistor and for 2N2222 used KSP2222A and for BC337 used Bc337-40.

What I am doing wrong.
 
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