CPAP/Centrifugal Blower

Heartleander81

I have the same too.
I haven't inverted anything either and only use 15% or more in the slicer.

But if there is a possibility that it starts under 15% I would be interested in it.

dc42

@heartleander81 @dhusolo fans generally have a minimum rpm (and hence PWM) that they can turn at.

jackantubis

I have the same type of CPAP, I can't go under 15% too, the board seems to have a minimum voltage startup. @dhusolo

Maybe you can configure in RRF 0% for the slicer matching 15% for the FAN to keep easier slicer setting to avoid false 0% with 10% set in the slicer. @dc42 ?

If someone found the CPAP board schematics I could investigate deeply (I'm electronic engineer)

dc42

@jackantubis if you set the L parameter in the M106 command to 0.15 then I think a command for 10% PWM should be translated to 15% PWM.

dhusolo

@dc42 I was hoping to figure out a way to not have to set min/max speed. Would it be possible to use an open extruder heater port?

gringo

I have connected to 5V PWM a servo for the Klicky Probe, is there any way to connect the CPAP differently and configure it as a fan?

dc42

@gringo most servos accept a 3.3V control signal, so you can probably connect that servo to a PWM-capable IO port instead.

gringo

@dc42

Thank you . I will try it.

Reine

Has anyone figured out a way to read the fan rpm?

dc42

@Reine I've looked at the datasheet for the controller board and it doesn't appear to provide a tacho output.

I guess you could use an opto isolator with a parallel diode and series resistor, connected across one of the motor phases, and connect the opto isolator output to an input on the Duet.

samlogan87

Simone has already done a write up on how to set them up.

https://www.modernmakes.ca/3d-printing/cpap-fan-guide

There is a speed output pin which is pin PG.

apak

try to set the minimo speed with L parameter of M106 and a blip to start at full

M106 P0 C"CPAP Fan1" S0 L.15 B.5 X1 H-1

You could also limite max speed just in case it blows too much with the X param

Exerqtor

Did you guys end up getting the speed signal to work or did you abandon it?

Reine

@apak I have it setup like this, without X last few % didn't do anything.

M106 P0 C"CPAP Fan" S0 B0.1 H-1 L33 X214

kazolar

I found the single 5V pwm output limiting, plus to get the most precise control, an analog 5v fed to the CPAP blower driver board is most accurate. Tried a few ways to do that and settled on this board https://www.amazon.com/dp/B079BH3SHX?psc=1&ref=ppx_yo2ov_dt_b_product_details -- it's powered by 24v, will take the pwm output of a regular fan output and create a clean 0-5v analog output. If you run it at 100-200hz you can get the low end to be around .5v, and that's as slow as the CPAP blower can go. I can go the full spectrum and have perfect output control. Not sure of another source for these boards, but I will use them for duet and for klipper configs since they're simple and the best part is the fan control is super accurate.