Duet 2 Wifi two power supply - Help



  • Hello,

    I have doubts about connecting two power supplies, one for duet and one just for heating bed. I found this discussion https://forum.duet3d.com/topic/5452/how-to-connect-two-power-supplies/7 and would like to understand how to connect an SSR to the heating bed using the best power supply. I did a quick sketch, but I don't know if it's correct.

    wiring_ssr_two_power.png

    red cable - positive
    black cable - negative

    Someone can help me!?



  • Why not use an external mosfet to power the 24v heatbed? I have the setup above but im using a 30amp external mosfet to power the bed using 2 psu 24v each...one is 250w for duet and motors and hotend, and the other is 350w only for heated bed!the wiring is very simple...



  • Or just forget the second power supply and feed the heater straight line voltage controlled by the SSR. Of course the heater needs to be rated for line voltage but it makes very little sense to install a power supply just for the bed heater.



  • @joaogoc said in Duet 2 Wifi two power supply - Help:

    I have doubts about connecting two power supplies, one for duet and one just for heating bed.

    what bed do you have? your schematic shows the bed being fed mains voltage; if you have a mains voltage bed then you don't need the 2nd power supply.

    if your bed draw less than 18A you can run the + from the power supply straight to the bed (pick the 500W supply if bed is more than 350w ofc) and run the negative through the bed output on the duet.



  • @bearer My bed is 400W and 24V. You mean it consumes 16.6A, correct? My power supplies have 20A outputs. Is it okay to just connect the 500W power supply directly to the Duet? Or can I continue to use an SSR?



  • @jens55 Only with a power supply, for a bed 400W-24V can I leave it like this?wiring_ssr_one_power.png



  • @joaogoc, this will not work. You are showing line voltage (L,N) to your 24V bed heater via the SSR!
    If you want to run your setup with one supply than you need to hook the bed up to the + and - outputs of your power supply in the current configuration with the SSR. This would work although I don't like running this close to the limit of the power supply. In the worst case scenario you are drawing 400W for the bed, a couple of 40W heaters for two nozzles, steppers and whatever else you are running and you could potentially max out the 500W supply.
    I would also double check the current capability of the Duet2's bed output .... I think it is rated at 18A which would mean that you don't need the SSR at all and instead run the bed directly from the Duet2.
    Again, my preferred configuration would involve a line powered bed heater via an SSR.



  • @jens55 said in Duet 2 Wifi two power supply - Help:

    a line powered bed heater via an SSR

    So how would this configuration be done? can you make a sketch? or simply a brief summary of the cable connections?


  • Moderator

    @joaogoc The L (Live) and N (Neutral) terminals are the input from your wall socket, ie 240V or 120V. That's fine if your heated bed is a mains powered one, but not if it's 24V! So connect the brown wire (going to the SSR) to + (24V) and grey wire from bed to - (Ground).

    Or just use the Duet bed output to power the heater. See https://duet3d.dozuki.com/Wiki/Choosing_the_power_supply#Section_Total_power_needed for advice on calculating power supply requirements.

    Ian



  • @joaogoc said in Duet 2 Wifi two power supply - Help:

    @bearer My bed is 400W and 24V. You mean it consumes 16.6A, correct? My power supplies have 20A outputs. Is it okay to just connect the 500W power supply directly to the Duet? Or can I continue to use an SSR?

    You could use an SSR that is made for DC; and you need to wire the 24v through the SSR not the mains voltage(N and L) like shown on your diagram.

    16.6A will be fine to run through the Duet however, it is rated for 18A (but the fuse is 15A, if the fuse blows you can put in a 20A fuse or use an external SSR or mosfet).

    Look at the link Ian provided and maybe you can get away with running everything off the 500W supply even.



  • @joaogoc said in Duet 2 Wifi two power supply - Help:

    @jens55 said in Duet 2 Wifi two power supply - Help:

    a line powered bed heater via an SSR

    So how would this configuration be done? can you make a sketch? or simply a brief summary of the cable connections?

    If you had a line powered bed heater than your drawing is correct as shown.
    The power supply feeds the Duet, the L (line voltage live) is connected to the SSR, the N (line neutral) is connected to one of the bed heater lines and the second bed heater is connected to the SSR output. Please use a thermal fuse ( attached to the bed and heater) between the SSR and the bed heater and make sure that the bed itself (and frame of printer) is grounded to line earth.


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