Expansion Header and Chamber Heater SSR

  • I am setting up my chamber heater and everything seems fine except I cannot get the SSR to turn on. I am using a Fotek SSR-25DA I can connect the device to +3.3 (pin3) and Gnd (pin2) and it turns on fine and the heater gets hot. When + terminal on SSR is connected to +3.3 (pin3) and SSR - terminal connected to Heater 7 (pin31). There seems to be no joy. The chamber temp sensor seems to be working fine.

    Here is the code in the config file:

    ; Chamber Heater
    M141 H7 ; heater 7 is the chamber heater
    M305 P7 R4700 T100000 B3950 ; heater 7 is monitored by a 100K thermistor with B=3950 and a 4.7K series resistor
    M301 H7 P-1 ; use bang-bang control for the chamber heater

    Through the web interface M141 S55 to set the temp, the Chamber says "active", but no output comes on.

  • administrators

    Assuming you are not using very old firmware, you should use M307 H7 B1 to select bang-bang control, not M301 H7 P-1.

  • Ok, I made that change, but still no luck getting the SSR to turn on

  • I may be quite wrong here, but would heater 7 not be H6 in the config since numbering of the heaters starts at H0?

  • Whoops. The heat came on, but no light on the SSR. It faulted out after only a couple seconds being active. I'll need to run the tuning once I get the covers on the machine, but it looks like it's working.

    Thanks for the help.

  • administrators

    Glad it's working. You may need to configure a large dead time using M307 to get the tuning to work without faulting, depending on where the thermistor is in relation to the heater.

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