Controlling my heated bed and SSR from DuetWifi


By jandan 21 April 2017 01:09

Member · 6 comments

I posted this question in another tread and was probably not very good at explaining my self.  This time a simple drawing is attached to describe the parts I have in mind.
Power for the heated bed is delivered from the DuetWifi card, i.e the terminal dedicated for this, NOT from any PSU external. It's 24 volt.
I suppose this would be more straightforward if a connected switch or button open the SSR with a signal.  But here I want, if possible, DuetWifi to do this instead, that after a command from the web interface.  How can DuetWifi, while delivering power over the terminal, close or open this, i.e control the SSR? Maybe there is a straightforward way for someone knowing more about the card or this type of wiring.  As you probably already notice, my insight is limited.
PS. I suppose Duet could just cut the power output. Then, why would I need the SSR?

Here is the SSR I have in mind: … cts_id=288   


Last edited by jandan (21 April 2017 01:17)


By Jackal 21 April 2017 02:14

Member · 116 comments

SSR is only needed when the power supply for the bed comes from sources other than the DuetWifi board itself.
Power to the bed (i.e. controlling temperature) is adjusted by sending g-code or using the web interface

Last edited by Jackal (21 April 2017 02:15)


By DjDemonD 21 April 2017 04:44

Member · 495 comments

If your heated bed is 24v and you intend to power duetwifi by 24v and the current of your heated bed is less than 15A then you don't need an ssr just connect the bed to the duetwifi directly.

If the bed is powered by 220v AC/120v AC then you need a DC-AC ssr. 

If the bed will be powered from a separate power supply or needs more power than 15A then you can use a DC-DC ssr but you can also use external mosfet boards like this or even a mechanical car relay. The duet wifi just switches this external switch using its heated bed output.

Do a bit more reading around about this technology it seems as though you're not fully grasping what you're doing and wiring this up wrong can be dangerous.

Last edited by DjDemonD (21 April 2017 04:46)


By deckingman 21 April 2017 08:13

Member · 799 comments
jandan wrote

How can DuetWifi, while delivering power over the terminal, close or open this, i.e control the SSR? ...........................

Simple answer. The heated bed terminals are not permanently live. They are switched on and off by the Duet.


By jandan 21 April 2017 13:20

Member · 6 comments

Thanks for all advice's. I had a small feeling that an SSR was not needed in this case, but would not rely on my own judgment in this case.