SSR stuck on???

  • I just built my RailCore II ZLT kit and the bed turns on and stays on. The red light on the SSR is on as well. If I disconnect the positive from the SSR it turns off.

    What I don't understand is, I'd assume the duet is not sending any signal with the bed off, so what would trigger the SSR to switch?

    It's all wired correctly.

  • As usual we'll take your word for everything being correct. That leaves the SSR to be faulty and the common failure mode is always on.

    If you wan't someone to review the rest you'll need to add some pictures and configs.

  • Some one recently accidentally inverted the heater control in the config leaving the heater to be on, when duet thought it was off.

    Other things to check is if there is signal going to the ssr board calling for heat. If you can disconnect the signal wires and there is still heat on the bed double check you haven't inverted the polarity by mistake if it's a DC bed. The body diodes on the mosfets will conduct in reverse polarity.

    Finally, adding a PS_ON triggered mechanical relay to isolate power to your heaters can really safe you some significant nastyness in combination with a maximum temp gcode setting.

  • administrators

    @gnydick said in SSR stuck on???:

    It's all wired correctly.

    How exactly have you wires the SSR to the Duet? Photo please.

  • @dc42 IMG_20191230_104512.jpg

    #1 to black wago
    #2 to bed loop eventually to white wago
    #3 bed pos
    #4 bed neg


    • Connected as is: bed turns on and stays on with heater off or on
    • #3 disconnected: bed stays off with heater off or on
    • #3 & #4 reversed: bed stays off with heater off or on

  • @DocTrucker as soon as I disconnect the signal wires, the bed turns off.

    With them connected, the bed is always on, even if I turn the heater on, which would turn it off if my config was inverted, if I understand that correctly.

  • Can you pull the SD card entirely, disconnect the bed connector on the Duet, power on, and carefully check if there is VIN across the bed terminals?

    If yes, then that would indicate that the bed heater mosfet has failed on.

    If not, Insert the SD card and check again, if there is now VIN across the terminals, then that would indicate a configuration issue.

  • @Phaedrux do I just set my meter to low voltage and touch to both terminals directly?

  • @gnydick I'm not familiar with your particular meter, but yes you'd set it to DC voltage in the range that would register 24v accurately. Touch + to + and - to -. Careful not to short anything else.

  • @Phaedrux yep, 24.1v 😞

  • @Phaedrux can I use a different connection to trigger the SSR while I wait for the replacement?

  • If its not covered by warranty and you want to use the SSR anyway you might get away with soldering a wire from the gate on the bed FET and run that to the SSR input. (you may have to invert the output if you do)

    Edit: sure, can def use any of the fan outputs instead.

  • @bearer any pointers on how to set that up? Would I just wire two of the pwm pins to the SSR and map the bed heater to that pwm?

  • Since the bed heater is being powered via SSR and the SSR input will accept lower voltage than VIN, you could use any other open heater or fan output with a little configuration.

    If the Duet came with the RailCore kit I'd seek a warranty claim.

  • @gnydick said in SSR stuck on???:

    @bearer any pointers on how to set that up? Would I just wire two of the pwm pins to the SSR and map the bed heater to that pwm?

    i'd use the "ground" from a fan, that ground is pwm controlled by the duet and you can use any supply voltage, the one on the fan output is convenient though. then unmap the fan if needed and map the heater. I'm sure some of the wizzards can help with the config if needed

  • @Phaedrux I am, but it will take time. I'd like to get everything else tested out while I wait.

  • administrators

    You can also use a spare heater output on the Duet or the DueX5.

  • Here's the directions for using a chamber heater. It's the same principal. Using an alternate pin for controlling an extra heater. The only difference for you is that instead of defining a new heater 3, you'd be altering the configuration for heater 0 (the bed on duet 2)

  • @Phaedrux thanks

  • It is highly unlikely that the SSR has failed since it is not stuck in the 'on' position. It is way more likely that there is a wiring error.
    Are you aware that the positive line will always be high no matter if the heater is on or off?
    Simply wiring the negative to ground will cause all these issues.
    Verify the ruting of the two control lines.

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