Switching a 3Kw Heater

Joined
14 May 2009
Messages
799
Reaction score
14
Location
Dundee
Country
United Kingdom
OK people, cross over electronics, and electrical here. I have a 3Kw immersion heater I am going to control with a a SONOFF smart controller. Now the SONOFF has a 240V output but limited current.

So as I see it 2 options.

Switch a 240C SSR that has a 20A switching capacity or greater
Switch a 240V Coil Relay that again has a 20A switching capacity or greater
Switch a 240C contactor that again has a 20A switching capacity or greater

SSR may have heat issues I assume.

So I see lots of options of contactors, that would work, anyone know if it is an issue, switching something like this many times per day? I like the contactor idea so if it fails it opens, etc.

Any other ideas?
 
Sponsored Links
Joined
7 Jul 2010
Messages
38,613
Reaction score
4,717
Location
Retired to:
Country
Portugal
There are such devices available. 16A will suffice.

You do not really need many times a day.

Immersions will switch themselves off after two or three hours when the water is hot and modern cylinders will retain the temperature for long periods.
 
Joined
28 Jan 2011
Messages
51,018
Reaction score
3,498
Location
Buckinghamshire
Country
United Kingdom
OK people, cross over electronics, and electrical here. I have a 3Kw immersion heater I am going to control with a a SONOFF smart controller. ...
What is that controller going to achieve that the immersion's thermostat, possibly plus some sort of time switch, would achieve?
Switch a 240C SSR that has a 20A switching capacity or greater
Switch a 240V Coil Relay that again has a 20A switching capacity or greater
Switch a 240C contactor that again has a 20A switching capacity or greater ...
Any of those would be OK and, as EFLI has said, 16A switching capacity would suffice. The difference between the second and third is, as far as I can tell, essentially 'semantic'.

Kind Regards, John
 
Joined
14 May 2009
Messages
799
Reaction score
14
Location
Dundee
Country
United Kingdom
There are such devices available. 16A will suffice.

You do not really need many times a day.

Immersions will switch themselves off after two or three hours when the water is hot and modern cylinders will retain the temperature for long periods.

What sort of device? I need to control the water to within 2 degrees. Most stats I find are 6C
 
Sponsored Links
Joined
14 May 2009
Messages
799
Reaction score
14
Location
Dundee
Country
United Kingdom
It’s a project for a brewing system. The switching differential on the stat with the heater is awful.
 
Joined
22 Sep 2009
Messages
648
Reaction score
101
Location
Nottinghamshire
Country
United Kingdom
It’s a project for a brewing system. The switching differential on the stat with the heater is awful.

Its about the best you're gonna get with simple ON/OFF control.

Now if you want to get into proportional control thats a different thing all together!
 
Joined
14 May 2009
Messages
799
Reaction score
14
Location
Dundee
Country
United Kingdom
My tests with the SONOFF work great, and give lovely control. I can then turn up the built in stat as a backup do say 50 C knowing that it will cut out as a second backup. But main control is covered. Will grab a 16A relay is see how it goes.
 
Joined
28 Jan 2011
Messages
51,018
Reaction score
3,498
Location
Buckinghamshire
Country
United Kingdom
It’s a project for a brewing system. The switching differential on the stat with the heater is awful.
One issue is that, unless the immersion is going to be in very small cylinder/whatever (and/or you have some 'mixer' within the cylinder), there will be appreciable temperature differentials between different parts of it, which obviously presents a problem for any sort of sensor/thermostat in a single location. Where is the sensor of your controller going to be located?

Kind Regards, John
 
Joined
14 May 2009
Messages
799
Reaction score
14
Location
Dundee
Country
United Kingdom
Yep, tank is 50L

I have 3 sensors, too, middle and bottom.

I have got the setup working perfect, just need to get this sorted so it can be left alone and self control
 
Joined
28 Jan 2011
Messages
51,018
Reaction score
3,498
Location
Buckinghamshire
Country
United Kingdom
Yep, tank is 50L .... I have 3 sensors, too, middle and bottom.
How does that work - does one of the sensors take priority for the temperature control? Do I take it that you are drawing heated water from the top?

Kind Regards, John
 
Joined
14 May 2009
Messages
799
Reaction score
14
Location
Dundee
Country
United Kingdom
So, I take the 3 readings and feed them
Into a PID control loop. Then with a little bit of logic I switch in and out the heater. the 3Kw has a very fast heat up cycle so that works well.

yes I draw off the top, seems to work great and tank holds temperature very steady. It’s actually a buffer tank I use In stainless with 50mm insulation.
 
Joined
28 Jan 2011
Messages
51,018
Reaction score
3,498
Location
Buckinghamshire
Country
United Kingdom
So, I take the 3 readings and feed them Into a PID control loop. Then with a little bit of logic I switch in and out the heater. the 3Kw has a very fast heat up cycle so that works well.
Fair enough, but how does the logic deal with fact that the temps measured by the three sensors will usually be bit different from one another - i.e. which one will it use to decide when to switch the heater back on and, if it's not the top one, what will be the temperature of water drawn from the top when the (lower down) sensor is 'satisfied'?

Kind Regards, John
 
Joined
14 May 2009
Messages
799
Reaction score
14
Location
Dundee
Country
United Kingdom
Top sensor used to take priority 1 reading, then middle used and compared to top. Bottom used to oversee and has a high limit set to shut things down if it goes crazy it gets stuck on. Basically at draw off is most critical temperature and it uses a high accuracy probe to grab that data to react fast.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Top