Control relay for more fans?



  • Hey!

    I have a duet 2 wifi and i'm currently using all of the fan-pins. For my BLV MGN Cube i'd like to be able to control four more fans (scrubbers) and i'm thinking a relay/ssr.

    The fans are today connected directly thru the PSU.

    Is there any documentation on how to add a relay for controlling more fans thru the duet web control?

    Thanks!


  • Moderator

    Do you have a free heater pin? If so, you could use that to control the relay for the fans.

    Which firmware version are you using?



  • If you're not using all the heater outputs you can use them for (brushless/non-inductive) fans as is. (add flyback diode to use with mechanical relays)

    Every other output like those on the expansion headers you need to use something that will not sink or source a current beyond the rating of the pin on the microcontroller (from memory about 2-4mA).

    Some SSRs can be driven directly by this, ordinary mechanical relays will need a transistor to drive the relay coil, and when you're adding the transistor you might as well drive the fan directly instead of using the relay as relays are not suited for speed control only on/off.

    Some relay modules will take a logic level supply in addition to the signal, these include the transistor to drive the coil (and diode to snub the transients).

    Refer to the duet schematic on how to wire a mosfet transistor for adittional fan outputs https://github.com/T3P3/Duet/blob/master/Duet2/Duet2v1.04/DuetWifi_Schematic_v1.04.pdf

    Alternatively put "mosfet module" the search query of your favorite online dealer to find something pre-made.

    edit: clarify non-inductive loads for heater output.



  • Yes, i've got one the heaters available.

    Any recommendations on what can of relay/ssr that would be suitable? Any wiring examples?


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