Operating multiple relays (not SSR)

  • Hello Duet community, i am upgrading my printer and decided to replace the controller with a duet wifi.
    I want to use 2 electromechanical relays (link bellow) to power a blower (for cooling the layers via air-duct) and a heated bed.

    alt text

    Both components are mains and though i have an SSR relay for the heated bed i would also like to add a electromechanical relay for added safety.

    Duet has only one PS-ON pin, is it possible to use other pins and control multiple relays via gcode?

    Is there a guide for that? I tried to follow some other posts but my knowledge of electronics let me down.

  • I've used a mechanical relay running off a heater output (bed) just make sure you set bang bang mode and that the relay is suitably isolated between the DC and AC side, optocoupled ideally. I've used opto coupled relay modules which also have flyback diodes as psON mains switches for the whole machine.

  • administrators

    Thanks @DjDemonD , @alkis as simon has mentioned you can control relays from a number of the outputs including fans and heaters. If you are using one as a fan control then the simplest option would be to use one of the FAN outputs if you are not already using them all for something else. You need to use bang bang control on a heater - for the fan set it to either full off (0) or fully on (1) and you will need to prevent the sicer from trying to set the fan to an intermediate setting.

    I can't confirm if that specific relay module will be OK being controlled by 12V or 24V as there is no data sheet on the listing and the JQC-3F(T73) relay datasheet is very limited, however the main issue is its a 5V relay. you might be able to get away with a series resistor to limit the current. alternatively you could use a 12V or 24V relay depending on what system voltage you are using. The final option is to use one of the spare IO pins on the expansion header (at 3.3V) and use a fet to convert that signal to 5V for driving the relay.


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