24V Heatbed with SSR



  • Hello,
    Yesterday I rebuilt my printer to a Filafarm NoBase - 218x218mm (MK2 / 3) / 24V / 200W.

    Installed is a Duet2 Wifi Board. I connect the heating bed via the
    included Solid State Relay SSR-500 with a separate 24V power supply.

    Unfortunately, the bed does't heat and I have no idea why it is not heating.

    When I gave directly 12V on the solid state relay, the bed warm up.

    Maybe someone has an idea what it could be?



  • The Duet 2 (Wifi and Ethernet) is rated for up to 18A bed heater current, so this is suitable up to 12 * 18 = 216W power, so no need of SSR.

    How have you do the wiring ?
    you have to connect one bed wire to +24V, and the other bed wire to BED- output on duet.
    https://duet3d.dozuki.com/Wiki/Choosing_a_bed_heater#Section_Bed_heater_driven_using_a_Solid_State_Relay


  • administrators

    @omerkel said in 24V Heatbed with SSR:

    Hello,
    Yesterday I rebuilt my printer to a Filafarm NoBase - 218x218mm (MK2 / 3) / 24V / 200W.

    Installed is a Duet2 Wifi Board. I connect the heating bed via the
    included Solid State Relay SSR-500 with a separate 24V power supply.

    Unfortunately, the bed does't heat and I have no idea why it is not heating.

    When I gave directly 12V on the solid state relay, the bed warm up.

    Maybe someone has an idea what it could be?

    Did you connect the + and - SSR control wires the right way round?



  • You say 'separate 24V supply' ..... I may not understand the circumstances correctly but this may be related to the separate supply setup.

    Why are you using a separate supply ?

    Besides making sure that the control voltage is applied to the SSR in the correct polarity, you need to make sure that the two independent power supply grounds are connected to each other. You can not supply a separate 24V positive and then use the control line from the Duet controller (which is on a different power supply)



  • @jens55 said in 24V Heatbed with SSR:

    You can not supply a separate 24V positive and then use the control line from the Duet controller (which is on a different power supply)

    I thought the whole purpose of an SSR is exactly to be able to use separate PSU's (or even mains power)... If you have your PSU's grounded on the mains side, would that not be enough?



  • The SSR is on the main line of 24V PSU, or at the 24V output, connected to bed ?



  • @DeltaCon said in 24V Heatbed with SSR:

    @jens55 said in 24V Heatbed with SSR:

    You can not supply a separate 24V positive and then use the control line from the Duet controller (which is on a different power supply)

    I thought the whole purpose of an SSR is exactly to be able to use separate PSU's (or even mains power)... If you have your PSU's grounded on the mains side, would that not be enough?

    OK, I misunderstood the setup. When I hear SSR it means control voltage on one side and mains on the other side. What you suggest (I think) is 12V control voltage on one side of the SSR and 24V DC on the other side heating the bed. Seems odd but ok.
    The outputs on power supplies are possibly 'floating' even though the ground of both supplies is connected to mains ground. Since my initial understanding of the setup was incorrect, let's forget about that possibility.

    Assuming that the control side of the SSR is run by the controller, the positive of the controller heat bed output would be connected to the positive terminal of the control side of the SSR and the negative of the controller heat bed output connects to the negative side of the control side of the SSR. I assume the SSR is suitable for DC output control.

    I don't think I understand the difference in setup between bed working and bed not working.



  • I don't connect the two grounds to each other. Maybe this is the problem.

    I have 12V control voltage at duet side and one the control side of the SSR
    and I also connect the positiv side from the controller to the positiv of the SSR.

    If I connect directly 12V from the power supply to the controller side of the SSR
    the heater is working. If I connect to the duet the LED from the SSR switch on but
    the bed is not heating.



  • Yes I connect the right way round.



  • Can it be that I have to change something in the firmeware?



  • The ground was not the problem. It also dosn't work after I connected both grounds together.



  • Let me give this one more shot. You have a 12V power supply and a 24V power supply.
    The 24V power supply is connected to the heat bed via the output side of the SSR.
    The input side of the SSR is controlled by the Duet (and consequently the 12V supply).

    If you hook up 12V positive to the SSR control input plus and you hook up ground from the 12V power supply to the ground of the SSR control input ground then you say the bed heater heats up ?

    If that is correct so far then we know the output side of the SSR is working properly and everything there is connected correctly.
    The LED on the SSR should be ON.

    Now you disconnect the 12V power supply and connect the Duet heater output to the SSR and you are now not seeing any heat in the heated bed ? Is the LED on the SSR on ?

    If the SSR LED is on then I can't see how there is no heat at the bed.
    If the SSR LED is off then there should be no heat on the bed and you need to establish what is happening on the heat bed output of the Duet.

    Keep in mind that the Duet switches the ground side of the heat bed output and not the 12V end.

    COuld you please confirm that my understanding is correct ?



  • @jens55

    "Let me give this one more shot. You have a 12V power supply and a 24V power supply.
    The 24V power supply is connected to the heat bed via the output side of the SSR.
    The input side of the SSR is controlled by the Duet (and consequently the 12V supply)."

    That is exactly what I do.

    "If you hook up 12V positive to the SSR control input plus and you hook up ground from the 12V power supply to the ground of the SSR control input ground then you say the bed heater heats up ?"

    If I disconnect the heatbed output from the duet and connect the 12V(+) from the power supply directly to the 12V positiv control input and also the ground from the 12V power supply to the ground of the SSR control input, the bed is heating.

    The LED on the SSR is i both configurations on, but the bed is not heating when connect to the duet.

    "Now you disconnect the 12V power supply and connect the Duet heater output to the SSR and you are now not seeing any heat in the heated bed ? Is the LED on the SSR on ?"

    The LED on the SSR is on but any heat in the heat bed.

    "Keep in mind that the Duet switches the ground side of the heat bed output and not the 12V end."
    Why is that importent?

    I can confirm that your understandig is correct.



  • Just to further clarify .... with the SSR hooked up to the Duet, when you turn the bed heater on, the light on the SSR goes on ... and if you turn bed heat off, the light on the SSR goes out? In neither case, after a bit of time for heat up, does the bed plate get warm ????



  • @jens55

    Yes, that is exactly my problem. The LED goes on and out, but in both status the bed plate didn't get warm.



  • I am officially stumped! Obviously the output of the Duet works as it is supposed to. Since the SSR switches fine with a 12V signal from the power supply but DOES NOT switch with the same 12V signal from the Duet, this just isn't possible.
    I would try to replace the SSR but chances are you haven't got a spare one sitting around and this is REALLY a long shot.

    Maybe somebody else has some other ideas. In any case, please keep us posted what the fault turns out to be.

    Sorry I can't be of more help.



  • Thanky you for your help. I will double check all again. Maybe I make a mistake.



  • I found out that when I connect the 12 V directly from the power supply to the control side of the SSR, the bed heating up and I can masure 1V between the plus and minus of the SSR(24V) main side.

    If I connect the SSR to the duet bed connector and switch on the bed I mesure 24V between the plus and minus of the SSR(24V) main side.

    Make this sence?



  • Yes, it makes sense.
    In the first case the SSR switches on so you have only a small voltage drop across the SSR.
    In the second case the SSR stays switched off so you see the full 24V across it.
    It just is really odd that you would get the LED on the SSR to go on (as in the second case you are describing) but yet the SSR itself stays off.
    It's a weird one alright ....



  • @jens55

    Yes, the LED is relly on.


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