using 12v fan in 24v setup.

sinole

I have been using marlin based boards for a long time and I am trying to use this platform. one of the things I did in marlin connected silent 12v noctua fans to 2 pin pwm and in marlin allowed them only 125 speed, which is 50% duty. that way output on the fan was 12v even on a multimeter. I don't know how I can do that with frequency numbers. how low of the frequency will mask as 50% lower voltage? configurator is suggesting 500 hz on 2pin fans, 250 will have the result that I need?

jay_s_uk

@sinole use a buck converter to supply 12v and do it properly

sinole

@jay_s_uk LOL , fam you gonna do this everywhere I ask this question? thank you, but as I am reading more a buck convertor reduces voltage by sending pwm signals. so I am doing it proper with less hardware and mess. in case you are interested in some literature. https://www.ti.com/seclit/wp/slup317/slup317.pdf
link above explains buck convertors

infiniteloop

@sinole said in using 12v fan in 24v setup.:

LOL

Nice link, but if you do not see the difference between the mechanism TI describes for a buck converter, and a raw pulsed signal, you come to wrong conclusions. So, instead of pouring malice on @jay_s_uk, better think again.

If you apply PWM to 24V, you still have 24V - just not all of the time. At 50% duty cycle, the multimeter may show an average of 12V, but the windings of your fan are permanently stressed with sharp pulses of 24V - what they are not built for.

droftarts

@sinole If you have Duet 2, see https://docs.duet3d.com/User_manual/Connecting_hardware/Fans_connecting
If you have Duet 3, there is an internal 12V regulator, and fan outputs have switchable voltage.

Ian

sinole

@infiniteloop I dont want to argue with jay, this is the way I ran my 3D printer for years, I just ask how I can keep doing it on reprap firmware. I have been told that i might be stressful to the fan. its a 12 dollar fan, if it works 5 years i'm happy not to put a bunch bulky buck convertor on my printer.

the thing with jay is that I was very respectful on his discord channel and we discussed this issue he didn't even want to listen. he messaged me profanities and banned me like a baby. anyway thanks for responses. I dont want to start my duet experience with a bunch of negativity. its already frustrating to setup a printer on a new platform, let alone going to fight with a whole comunity.

engikeneer

@sinole if you do want to do this, then you don't do it by setting the frequency (how often it send the pulses), you do it be setting the duty (how long the pulses are as a proportion).
How exactly to do this depends on what the fan is for, and what firmware you have. Give us some more details and we can suggest something

sinole

@engikeneer duet 2 wifi, and i dont have a firmware yet. obviously I want RepRap firmware. I agree with you. i need to assign the duty. I don't know how, the config is only calling for frequency. thank you

engikeneer

@sinole what firmware version? Send M115 via console to check.
The syntax for RRF3 is different to RRF2

droftarts

@sinole As already mentioned by others, running a 12V fan at 24V with 50% PWM will stress the fan, may cause overheating, fire, death etc. Using a 12V buck converter is the better way to do this. However, if you REALLY want to use 24V...

To set 50% PWM and frequency depends on firmware version (I'd recommend using the latest RRF 3.4). See https://docs.duet3d.com/User_manual/Connecting_hardware/Fans_connecting#firmware-settings

Assuming RRF 3.4, define the fan and set the fan frequency with M950, eg:

M950 F0 C"fan0" Q500 ; create fan 0 on pin fan0 and set its frequency

Set the maximum fan speed/PWM frequency with the X parameter in M106. This should limit PWM to 50% even if fan speed requested in M106 (S parameter) is 100%:

M106 P0 S0 X0.5 ; set fan 0 value. Thermostatic control is turned off. Fan is initially off. PWM limit set to 50%

Ian

infiniteloop

@sinole Generally, you should provide your devices with their specified voltages - anything more than that can be harmful, dangerous or both. As I already explained, 24V with a 50% duty cycle are still 24V, not 12V, so @jay_s_uk’s answer to your question is right.

I’m happy not to put a bunch bulky buck convertor on my printer

If you run multiple 12V fans, have a look at @droftarts' link: instead of wiring a buck converter to each of the fans, you can use a single (cheap) 12V PSU with the Duet2. From the link:

The 3-pin jumper (V_FAN) allows you to select whether all fans (three controlled fan connectors FAN0, FAN1 and FAN2 plus two always-on fan connectors) are powered from the VIN supply or from the Duet's 5V supply. You can supply a different voltage to the centre pin of the 3-pin jumper, pin V_FAN, to run fans at different voltages.

This is possible as the mosfets on the board switch to ground, not to VIN. It offers you the additional ability to control the fan’s speed by PWM - without risking the fans.

sinole

@droftarts thanks alot

sinole

@infiniteloop thank you I will investigate all options. if only noctua had 24v fans. I really cant stand other fans. my printers are in my office and everything other than noctua screams at you. I tired many brands.
thanks everyone for the help.

infiniteloop

@sinole said in using 12v fan in 24v setup.:

everything other than noctua screams at you

D'accord. I think, your noctuas deserve a distinct 12V PSU - that's a clean solution, and they are worth it. Good luck!