Wiring electromagnets and fans



  • Hi all,
    I am wondering if electromagnets can be handled like fans in generall and if it is safe to connect an 24V 3,6W electromagnet directly to a fan output. Also I would like to know if there is any risk to wire two fans in parallel to the same output.

    Thanks in advance!



  • Coil electromagnet: This depends entirely on the electrical characteristics of the electromagnet. Maybe 24V 3.6W means 0.15A in steady state (150mA). This is probably OK on a fan output. BUT... those numbers are "steady state"

    I would consider a simple diode to block back-emf from the collapsing magnetic field when the coil goes off...

    Two fans in parallel will work if:

    1. Both fans are the same voltage rating and it matches the fan output.

    2. The two fans current rating, summed, does not exceed the current rating of the fan output

    3. You do NOT PWM them. Run them at 0, or 255. Having said that, PWM might work, or it might act really weird with two in parallel.



  • Thanks for your fast reply 🙂
    Doesn't the Duet Wifi have a fly-back diode to prevent damage caused by back-emf?
    Do the 1.5A max current in the wiring diagram apply to each output or to all of them together?
    What would be the problem with PWM?



  • PWM might work. It won't hurt anything to try. The main problem will be the fans interacting with each other. All motors are generators as well, and during the PWM "off" moments, one fan might drive the other,etc.

    I don't know about the flyback for sure, you can check the schematic.

    I'm about 90% certain the 1.5 is per output.



  • @Danal said in Wiring electromagnets and fans:

    Coil electromagnet: This depends entirely on the electrical characteristics of the electromagnet. Maybe 24V 3.6W means 0.15A in steady state (150mA). This is probably OK on a fan output. BUT... those numbers are "steady state"

    I would consider a simple diode to block back-emf from the collapsing magnetic field when the coil goes off...

    Two fans in parallel will work if:

    1. Both fans are the same voltage rating and it matches the fan output.

    2. The two fans current rating, summed, does not exceed the current rating of the fan output

    3. You do NOT PWM them. Run them at 0, or 255. Having said that, PWM might work, or it might act really weird with two in parallel.

    Sorry to raise this from the dead. But would it be possible to have a fan output go to a ssr or external mosfet to switch a coil electromagnet. It will be fan at 0 or 255. Nothing in between. That way to help isolate the higher current circuit from the fan circuit.



  • Sure. Mosfet or SSR is a very valid way to drive almost anything from a Fan output.


  • Moderator

    @tekstyle I think that should be ok.


  • Moderator

    @Danal JYNX


  • administrators

    To clarify:

    • You can run an electromagnet/solenoid directly from a Duet fan output. Early Duet WiFis didn't have flyback diodes built in, but more recent ones do (from version 1.03 AFAIR).
    • Max continuous output current is 1.5A per fan, but you may need to increase the current rating of the fan fuse. Up to 2.5A is allowable for a short period e.g. half a second.
    • So no need to use a SSR unless the holding current will be >1.5A.
    • You can certainly use a SSR if you prefer. If it is a 24VDC solenoid, you will need DC-DC SSR.


  • thank you for the clarification and the confirm from all of you! it's a 24V electromagnet but I think I might isolate it either way. I don't want to end up blowing things as it will be on continuously and only switched off and back on during tool change.



  • i was doing a test on a 12V .25A electromagnet using the Fan8 output on the duex 5.

    M950 F8 C"duex.fan8" Q500 ; create electromagnet on pin duex.fan8 and set its frequency to 500 MhZ

    I use the below to switch on and off
    M106 P8 S1 ; power on
    or
    M106 P8 S0 ; power off

    what I noticed is that it gets too hot to touch when on, and when off, it still is very warm.

    is there anyway to lower the working and standby temperature?


  • administrators

    @tekstyle said in Wiring electromagnets and fans:

    is there anyway to lower the working and standby temperature?

    With M106 P8 S0 it should turn off completely and eventually cool down to ambient temperature.

    To reduce the temperature when it is on, you can try a sequence like this:

    M106 P8 S1 ; turn on at full power
    G4 P1000 ; wait 1 second
    M106 P8 S0.5 ; reduce to half power

    assuming that half power is sufficient to hang on to whatever the solenoid is pulling in.



  • @dc42 interesting. i'll give it a try. i do know that it takes like a split second for it to become demagnetized so this may work. I was curious of the frequency would affect it (eg. M950 F8 C"duex.fan8" Q500). or should i just make this zero frequency (Q0)?


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