Speed controller with immersion heater?

[nigel jones 5Participant @nigeljones5]

Help sought. I have a tank in my workshop – nothing to do with the domestic water supply – with a standard type immersion heater fitted. I want to be able to finely adjust the temperature of the water and wondered if simply plugging it into a 4kw 240v variable speed control unit would work, the type that are advertised for controlling fand and dimmer switches? The heater has an adjustable thermostat but its not designed for constant adjustment.

[nigel jones 5Participant @nigeljones5]

[David George 1Participant @davidgeorge1]

You need a proportional temperature controller you need to look up on line as there are many suppliers. As you set temp a thermocouple measures temp and switched power as necessary.

David

[John RuddParticipant @johnrudd16576]

You would be better off using a PID temperature controller with a thermistor to provide feedback of the water temp…..( you might not need the Derivative function…    )

A speed controller is just open loop…..

Edited By John Rudd on 16/07/2018 21:10:47

Edited By John Rudd on 16/07/2018 21:14:19

[EmgeeParticipant @emgee]

Hi Fizzy

I agree the thermostats fitted to immersion heaters may be a bit coarse for some applications but they do seem to be consistent in switching temperature.

For finer control you will need to fit an electronic probe and control that will switch the element on for short periods until the set temperature is attained. Positioning the probe is important but it is unlikely to achieve all water at the same temperature if you don't have positive means of circulating it in the tank.

By whichever electrical method used for heating the water temperature will be controlled by a thermostat or similar device, even your variable speed control unit.

Emgee

[John RuddParticipant @johnrudd16576]

Posted by Emgee on 16/07/2018 21:09:48:

Hi Fizzy

I agree the thermostats fitted to immersion heaters may be a bit coarse for some applications but they do seem to be consistent in switching temperature.

By whichever electrical method used for heating the water temperature will be controlled by a thermostat or similar device, even your variable speed control unit.

Emgee

Err…how does the speed control know what the temperature is with no feedback?

[EmgeeParticipant @emgee]

Posted by John Rudd on 16/07/2018 21:13:00:

Posted by Emgee on 16/07/2018 21:09:48:

Hi Fizzy

I agree the thermostats fitted to immersion heaters may be a bit coarse for some applications but they do seem to be consistent in switching temperature.

 

By whichever electrical method used for heating the water temperature will be controlled by a thermostat or similar device, even your variable speed control unit.

Emgee

 

Err…how does the speed control know what the temperature is with no feedback?

For finer control you will need to fit an electronic probe and control that will switch the element on for short periods until the set temperature is attained. Positioning the probe is important but it is unlikely to achieve all water at the same temperature if you don't have positive means of circulating it in the tank.

John, I suggested a thermostat but your guess is as good as mine for such an application.

Emgee

 

Edited By Emgee on 16/07/2018 21:32:17

Edited By Emgee on 16/07/2018 21:33:28

[John RuddParticipant @johnrudd16576]

Emgee, as an Instrument Engineer, mine is not a guess…40 years plus served in industry…I dont offer advice lightly..

[EmgeeParticipant @emgee]

Posted by John Rudd on 16/07/2018 21:57:23:

Emgee, as an Instrument Engineer, mine is not a guess…40 years plus served in industry…I dont offer advice lightly..

John, I had already suggested a method of control, almost the same as your suggestion but I did add a circulator would be required to ensure even water temperature in the tank.

To use a motor speed controller is a no go as suggested by my reply, but it would heat the water by switching the supply on, just add a stat as 2 wire on/off control cct.

Emgee

[nigel jones 5Participant @nigeljones5]

thanks all

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