PWM through 24v to 12v converter?



  • im using a sanyo tandem counter-rotating fan for an exhaust and its 12v 2A and my duet is on 24v. is there a specific type of voltage converter that can handle pwm? i tried a lm2596 buck converter but even with the fan setting at 10% the fan went full blast and popped the 1A fuse. ive heard of stacking diodes in series but im not really trying to solder up like 30 diodes.



  • Wire the buck regulator input to an always-on fan output. Wire the positive wires of 12V fans directly to the buck regulator output, and the negative wires to the FAN- pins of the controlled fan outputs as usual

    https://duet3d.dozuki.com/Wiki/Connecting_and_configuring_fans#Section_Using_12V_fans_when_VIN_is_24V

    I use the same way with 5V fan and 24V Duet



  • @pipersw said in PWM through 24v to 12v converter?:

    and the negative wires to the FAN- pins of the controlled fan outputs as usual

    YES

    PWM on Duet boards is pulsing the negative (ground), not the positive.



  • ahh, i get it now, thankyou.



  • couldn´t we just set it by

    ¿¿¿???

    M106 P1 S1 I0 F500 H1 T45 X127

    the X is a max pwm limitator



  • @pipersw
    So we could just use one buck converter to lower from 24 to 12, and plug all our 12v vcc pins there, and all the gnd pins to the actual fan ports?



  • @apak said in PWM through 24v to 12v converter?:

    @pipersw
    So we could just use one buck converter to lower from 24 to 12, and plug all our 12v vcc pins there, and all the gnd pins to the actual fan ports?

    Yes, assuming the buck has current capacity for all the fans tied to it.



  • @apak said in PWM through 24v to 12v converter?:

    couldn´t we just set it by

    ¿¿¿???

    M106 P1 S1 I0 F500 H1 T45 X127

    the X is a max pwm limitator

    No. PWM of 50% at 24V is NOT the same as 12V. Not unless there is a fairly large capacitor or inductor in the output circuit.



  • @Danal LM2596 can handle up to 3A as I recall,



  • @apak said in PWM through 24v to 12v converter?:

    @Danal LM2596 can handle up to 3A as I recall,

    Yeah, and most fans are VERY small mA load. Most setups will work fine with a buck on + to the fans and each fan negative to the negative of a separate PWM connector on the Duet.

    Just something to think about if you plan to parallel a lot of stuff, or have a very limited converter, or whatever.



  • Not much really, only the noctua 12v fan right now, but I wanted to know if it would work.

    I am using old 12v fan from my own stash of spare parts...once I´ll finish them off will use 24v fan or 5v fan...i will check then wich ones to use.



  • ok so i wired it up correctly and it worked...kinda. it wasn't liking 500hz frequency so i upped it to 25000 and it worked great for a moment but after about 20 seconds of 50% throttle the fan slowed way down.

    this fan has PWM control wires. but im not sure how this would work, if i give it 12v for power it just turns on, shouldn't it do nothing without the control wires connected?

    i can try hooking the pwm wires to the ground on fan2 but i have a suspicion that its just gonna go full blast as soon as i turn the printer on. because if the ground is pulsed then the fan dosent know whether or not the pwm wires are even hooked up at first. maybe im thinking about this too hard. does the I1 parameter take care of this problem or does that not work through a buck converter?



  • Individual fans vary. Try a two wire fan if you have one. Also try frequencies in the area of 30Hz to 100Hz.



  • okay so i wired it up with the pwm wires. at first the pwm signal it wants is inverted so that gave me a good laugh, but it is working correctly now. i cant turn it off all the way but thats okay as its just an exhaust fan. however, because the signal is inverted, whenever i reset the firmware the fan goes full speed for about 1.5 seconds. is there something i can do to slow its speed up, like add a capacitor?


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