Controlling an AC fan speed depending on temperature

I need to control the speed of 3 AC fans deepening on the input from some temperature sensors. I have done a temperature controller that will turn relays on and off but i think AC motor speed controller is a little more complex. Any advise or tips on the best way to approach this?

Fans usually don't consume tons of Amperes so I suggest using logic SSRs, Solid State Relays.Just use
PWM for the SSR.

they only draw 0.34A at 240V so do you think that's an option

jamesb123:
I need to control the speed of 3 AC fans ......
.......i think AC motor speed controller is a little more complex.

You are 100% correct. speed controllers use a completely different input.
For an AC speed controller, you can blow it up by disconnecting the motor with it running so relays are out. [ if you have a speed controller ]

What you need to do is to stop looking at what you plan to do
Start by completely detail what you already have.
make, model, data sheets, etc.

[ assuming you are saying you have a VSD ....]
Control signal may be serial, RS232 or RS485 or USB or some other serial, MODBUS or some such.
Or they may be analog, meaning PWM.
if you have one VSD for 3 motors and they all ramp up and down as one motor, then all you need is to the variable input control.
If you have 3 motors and each has a VSD, then you need 3 outputs.

This project needs to start the proper way.
figure out what you have, with details and data sheets.
figure out what you want to do
determine if the 'simple' solution will work
verify compatibility of parts.

In the end, it may be simple SSR's without a controller, but they way to determine the best method is to know what you have.

It depends on the motor type James; to speed control most you need to provide an alternating voltage at the frequency you want it to run at.
Not an easy task.

Honestly it would likely be cheaper and easier to replace the motors!

jamesb123:
I need to control the speed of 3 AC fans deepening on the input from some temperature sensors. I have done a temperature controller that will turn relays on and off but i think AC motor speed controller is a little more complex. Any advise or tips on the best way to approach this?

Give details on the motor type and go from there.
Just quoting fan motor covers a lot of territory.

From the 240v 0.34A I'm guessing a cap run motor.
If that is the case, one can go with series capacitors, differing values, differing speeds.

Thanks for the advise, the fans are Blauberg Centro 125 spec sheet https://blaubergventilatoren.de/uploads/download/rvu10687840043centro_125en2.pdf
https://blaubergventilatoren.de/uploads/download/centro_v2_bl_ind_catalogue_2020_07_en.pdf. The models i have don't have the temperature and speed control knobs. They simply have an AC 240V Live, neutral, and earth connection.
I have also brought a 4 speed fan controller switch for them
https://www.tlc-direct.co.uk/Technical/DataSheets/Westinghouse/EN78800_Instructions.pdf
One of the problems is speed 1 is very slow, 2 is quite slow, 3 is nearly full speed and 4 is full speed. There is a massive jump in the middle right where I need the control. Ideally id like to ramp the fan speed up between 2 user input temperatures say 10 and 30C. Is this possible? I did think I could utilise the fan speed controller switch and instead of the 4 position rotary switch I could have a variable resistor or capacitor controlled by the Arduino, or is my understanding completely wrong on this one. It wold mean reverse engineering the switch as the 4 positions on the rotary switch could do 4 completely different things I guess? And yes the 3 fans need to controlled separately depending on the temperature inputs so fan 1 may be off, fan 2 100% speed and fan 3 50% speed. Although id prefer a linear speed control I suppose I could live 5 evenly spaced settings say off, 25% 50%, 75% 100% speed if that makes it a lot simpler.

I've just found this which is quite interesting AC Fan Speed Control using Arduino and TRIAC. I could replace the potentiometer with a value calculated by the Arduino depending on the users input min and max temperature set points and and actual temperature input from a sensor? Looks like it's going to be another step learning curve for me into electronics

Almost 80 Watt at 240 Volt. Have respect for the power used!
I suggest SSR made for AC and 240 volt * 1.414 + margin and regard the need of eventual cooling.

jamesb123:
AC Fan Speed Control using Arduino and TRIAC.

Sorry, I don't accept coockies etc. so no visit there.

Thinking outside the box i could go with a very large 12vdc computer fan like Noctua NF-A14 IndustrialPPC 3000RPM PWM (140mm) High Performance Fan 4716123315452 | eBay or BitFenix Spectre PRO 200mm Fan White LED black | eBay. I'd need to check the static pressure as they need to push air down a length of ducting so there is significate resistance unlick a computer case. But this may simplify the problem somewhat.

Railroader, try the link to his YouTube video instead AC Fan Speed Control using Arduino and TRIAC - YouTube

Thanks!
There is a huge difference between that fan and the fans You showed first.
This second fan is excellent for blowing air at f ex a heatsink. However, it doesn't manage to create air preassure. Don't try to blow (push) air through pipes, channels etc where there is some resistance against the airflow. The counterpreassure will make the fan like stall, rotate without moving the air.
The fans You showed first will manage to create bit of air preasure.

Could make an easy picture or give a more detailed description of what/where/how way You want the air to flow?

jamesb123:
I have also brought a 4 speed fan controller switch for them

The reason for the jump is the values of the capacitors.
In a 3 speed for example, low speed would be around 1.5uF and medium around 2.5uF, high speed then shunts them out.

These caps are easily available on places like Ebay for a couple of dollars so playing with values and combinations of values should get you where you need to be.

What does that video tell? It looks like djungle-woodoo to me. Lots of unexplained details.

my experiments

I control a 2kW heater with Triac but I tested it with a fan too

that look great Juraj, I might get the bits I need and have a go at building one and see how it goes thanks

looks like someone has already taken the hard work out of this i might buy one and give it a try. https://robotdyn.com/ac-light-dimmer-module-1-channel-3-3v-5v-logic-ac-50-60hz-220v-110v.html
Shame it's 2-3 weeks shipping id like to have a go next week when I'm off

Using fans to either distribute heating from a heater, or cooling down other hot stuff is very effective. Be surpriced how only some small fan wind does a lot!

jamesb123:
looks like someone has already taken the hard work out of this i might buy one and give it a try. https://robotdyn.com/ac-light-dimmer-module-1-channel-3-3v-5v-logic-ac-50-60hz-220v-110v.html
Shame it's 2-3 weeks shipping id like to have a go next week when I'm off

try to find it in a local internet shop. many sell Robotdyn products. it is not a noname anymore