Need help wiring Heated bed - dedicated PSU - Releay.

  • Hi .
    I have a 360W heated bed a 600W psu 24V and I would like to drive the bed with a relay for security reasons also in the future I am planning to use a heated bed > 360W.
    I am breaking my head searching how to wire all thi things togheter. Is there anyone who can help me?


  • Yeah I used to have this setup. Okay I am assuming an electro-mechanical relay like this:

    There are two connections labelled 85 and 86, connect these to the heated bed output on the duet wifi you can use quite small cables here these won't carry much current. I think they need to be the right way around, but it won't cause damage if they aren't. Wire them one way around, turn on the heated bed (make sure bang bang mode is on, not PWM, bang bang is the default mode for bed heaters) and if the relay clicks once then this bit is done, if not swap them over and try again. If it is clicking on/off rapidly then PWM is enabled, this won't work with mechanical relays, you need to have B1 in your M307 for the bed heater in config.g.

    Now run a big thick, wire from your PSU negative to the heated bed negative.

    Run a similarly chunky wire from the heated bed positive to the connector labelled 87 on the relay, then from the remaining connector labelled 30 to the PSU positive.

    Its best to have a fuse in either the heavy positive wire somewhere or the heavy negative wire. Use an automotive fuse and allow a little headroom, so 360W/24v = 15A so a 20A fuse would be perfect.

    If its a solid state relay its pretty much the same wiring but the connectors will be labelled differently.

    Just an aside but these external mosfet boards are IMO a better choice, you can use PWM for smoother control, and no clicking.

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