RRF3 limit max heater PWM?



  • need to run a 12V heater on a 24V rail "for a few weeks" ... dual extruder setup, one heater is 24V other is 12V, is there a way to setup one heater to never use more than 50% pwm? I don't see that M950 have this option ... not a big issue if not possible but would skip adding external hw if I can solve it in fw 😄



  • @smece I will assume here that you know it is highly discouraged to use 12V heaters with 24V power supply. Also you would need to limit it to 25% and not just 50. PWM limit is not applied via M950 but via M307 Snnn parameter. In your case that would be M307 S0.25. But again: not a good idea - but I think you know that already.



  • yes, not a good idea, I agree 100% but I'm waiting for new ones to arrive and I wanna do some simple tests where this would be acceptable ... 50% will do these are low power heaters with 50% pwm of 24V they will be just fine 🙂



  • @smece said in RRF3 limit max heater PWM?:

    50% will do these are low power heaters with 50% pwm of 24V

    if you double the voltage you quadriple the power.

    so you would be running a 30W heater at 120W at full power.
    that is why @wilriker said 25%



  • @Veti said in RRF3 limit max heater PWM?:

    if you double the voltage you quadriple the power.

    so you would be running a 30W heater at 120W at full power.

    And consequently a 12V 30W heater will be running at around 60W with 24V 50% PWM.


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    @smece said in RRF3 limit max heater PWM?:

    need to run a 12V heater on a 24V rail "for a few weeks" ... dual extruder setup, one heater is 24V other is 12V, is there a way to setup one heater to never use more than 50% pwm? I don't see that M950 have this option ... not a big issue if not possible but would skip adding external hw if I can solve it in fw 😄

    This is possible using the S parameter of the M307 command. But as others have noted, it is also unsafe. The printer should most definitely not be left unattended.



  • it's crappy 18W heater on the huge piece of alu block so no worries, it's plenty safe, and everything is not even in beta stage so nothing is unattended and I have a finger on the power non-stop 😄 ... it's just that I missed M307 as there's "update" on the rrf3 page not mentioning S so I didn't bother to check main gcode doc to read the rest of the parameters that didn't change 😄 so I wrote here 🙂 ... as for ohm's law It's been 30years since I learned it but those things you don't forget that easy



  • actually 12W, even worse 😄 in theory it would behave like ~50W 24V but not sure how good the inside of it is (I seen some where there's huge gap between wires and outter metal, no sand/ceramic/fire-cement between thermal wire and casing) and in case is not good it can burn out... so I wanna control the max pwm output for just in case 😄 .. 50% will do the trick 🙂 (mind, I'll start with 10% to test if it works at all taking into account the firmware is beta too)


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