Heating element control

Hi folks.
I'm trying to control the temperature of an element in a fan heater. I can find a ready made thyristor module with an adjustment potentiometer on ebay or Amazon which would work with no problems. I would like to replace the manual potentiometer with something that can wirelessly adjust the voltage to the thyristor module. I already have a wireless light dimming unit and was wondering if I could combine this with the thyristor module to control it. Obviously I can't do this directly because the dimming unit is designed for small loads with low currents but the heating element is a high load device which will draw considerably more current than the dimming module can handle.

Has anyone else here tried to do something like this before?

Once I have achieved this it should be relatively simple to control the temperature in a closed loop system in Node Red by using a Sonoff device to monitor the temperature and set high and low limits.


It seems you want to variably control the heating element via node Red. You are probably going in the right direction with a dimmer module but you don't say how much current the element draws at full on or what the voltage is.

What is the application for this? Very often if, for example, heating a room or greenhouse with a fan heater then on/off control (using a relay or SSR) where the on/off duty cycle varies between 0 and 100% and with a period of a minute or two is perfectly satisfactory. The control can be done using node-red-contrib-pid with the time proportioned on/off cycle being handled by node-red-contrib-timeprop. I use this for my greenhouse and conservatory and get temperature control better than 0.5 degrees. On/off control is much simpler (and cheaper) than linear control.

@Colin got to the point faster. You can get a SSR good for 40 amps fairly cheap. They will trigger with a 3.3 v input and work well. Put a good heat sink on it though.

Reading your first post again I am not sure you even need the pid control. If you can get away just with simple on/off control with some hysteresis to it switching on and off rapidly with the noise in the temperature sensor then just use a hysteresis node and a relay or ssr output.

Thanks for the comment chaps.

As I would like to control the element in a fan heater in my front room (its built in to an imitation fire surround with flame effect) I guess i could find a solid state relay which could be configured to switch on and off via a Sonoff type device. A mechanical one would be too noisy and I guess its life time would be reduced due to constant switching. I will have to take the fan heater apart and try to separate the heating elements from the rest of the circuitry. The Node Red part should be relatively easy, just the hardware I'm having to have a good think about. I have an old stand alone fan heater in the shed which I could practice on. Don't be too concerned folks as I am a retired electrician. I'm well aware of the safety issues concerning electricity.

I'm doing pretty close to what you are describing with a node mcu - basically a esp8266 - and a SSR using MQTT. Two pieces of hardware and some bubble gum. Kidding about the gum.

I am sure you will know about it, but for anyone else who might find this, if you hack into a fan heater to drive the element directly then be very careful not to accidentally take the over temperature trip out of the circuit. Otherwise if the fan fails or seizes, but the element remains powered, the heater will go up in smoke, literally.

Very good point there Colin.

I have fitted a Sonoff 16 WiFi unit to the incoming supply on the electric fire. It works well and can handle up to 16 amps of current. It is under the control of Node Red whilst monitoring the room temperature with another Sonoff device. In node red I have introduced some delay by averaging a number of measurements. It works quite well. Thanks for all the suggestions.

I wouldn't recommend using the sonoff relays at much more than half their rating if you want them to last any length of time.

I'm not using all the elements on the fire. Its on its lowest heat setting so only 500w. Only 2 or 3 amps at most.

This topic was automatically closed 60 days after the last reply. New replies are no longer allowed.