Thermostatic fan at 25%?

fulg

Hello, I am trying to configure bay fans that automatically turn on at a specific temperature. This is usually quite trivial and super common for the hotend fan, however in my specific case it does not seem to work as intended.

Here is the relevant config snippet:

M950 F2 C"out5" Q30                 ; Create fan 2 (electronics bay) on pin out5 and set its frequency
M106 P2 S0.25 H1 T50 C"Bay"         ; Run the fans at 25% if the hotend is over 50C

This seems quite trivial however it absolutely does not work, the fans do turn on when Heater1 hits 50C but they run at 100% speed. I know because changing S0.25 for S1 in the M106 keeps the same speed (also those fans are unbearably loud at full speed).

Interestingly, using S0 in the M106 does not keep the fans off, they simply run slower (I would guess 50%) when the trigger temperature is hit.

Looking at the documentation for M106, I don't think this is normal, is it?

For now I have avoided using thermostatic mode for those bay fans and do a manual M106 P2 S0.25in my start Gcode to run them at 25% when printing, but I'd rather those fans be controlled automatically.

I am running RRF 3.2.2 on a Duet3 Mini5+, but this also occurred on my older Duet2Ethernet+Duex5 setup on the same firmware, I just didn't get around to posting about it.

OwenD

@fulg
Do you have a data sheet for your fan?
I recently purchased a 4 wire fan to use on a water cooler and discovered that although it is pwm capable, it is designed to run at all times.
When turned "off" it goes into a quiet mode at low rpm. When the sensor reaches the configured temp, it will increase speed as expected.
You may also be not using the correct pwm frequency.

Phaedrux

@fulg said in Thermostatic fan at 25%?:

Q30

Have you tried other frequencies? Q30 is pretty low.

fulg

@owend The problem only occurs when thermostatic mode is enabled... without thermostatic I can control the fans just fine (at a low PWM frequency).

Unfortunately those fans turned out to be a fairly bad purchase. They are Sunon MF60201V3-1000U-A99 (datasheet is here).

@Phaedrux I've had to reduce the PWM frequency a whole lot due to noise/whine, I do not recommend those fans to anyone.

The behavior is similar but different with a more traditional 250Hz frequency: the fans are running at ~50% (not 25%). At 25% they are near silent but 50% is quite noisy so it is easy to hear the difference.

Does thermostatic mode enforce a minimum/maximum PWM frequency?

OwenD

@fulg
For completeness, what is your M308 setting for this fan?

Also the fan is not PWM compatible.
From the data sheet

*7. DO NOT use power or ground PWM to control the fan speed. If the fan speed needs to be adjusted, please contact SUNON to customize the product design for your application. *

zapta

If you want to control two wire fans with PWM, this upcoming adapter may interest you

https://forum.duet3d.com/topic/21680/designing-a-pwm-to-analog-mini-board-for-fans?_=1617508112834

o_lampe

@fulg
If you want to run them at 25% only, why not use a resistor /potmeter in line with the fan(s)?
Then just switch them on above 50°C=> Job done

fulg

@owend I understand this fan is "not" PWMable but in practice it works, it is just super noisy. I don't think it changes anything in this case however.

what is your M308 setting for this fan?

Since you asked: M308 S1 A"Hotend" P"temp2" Y"pt1000", but I can reproduce this on a spare Duet2 Wifi board with a more typical M308 S1 P"e0temp" Y"thermistor" T100000 B4138.

In order to prove my point and eliminate the fan and frequency from the equation, I hooked up my logic analyzer to measure the PWM duty cycle (the "fan" here is a simple resistor), and this is what I got:

The config here was M106 P4 S0.1 H1 T20 so it should have been running at 10%, however the firmware did indeed send 50% instead of what I configured. You can also see I reverted back to the default 250Hz frequency.

If I disable thermostatic mode, then the fan control works as expected with M106 P4 S0.1:

(the duty cycle is inverted so 90% here means 10% in RRF.)

So I think this proves there is an undocumented limitation (or hopefully just a bug) with thermostatic mode and PWM cannot go lower than 50% in that mode.

@o_lampe that's not a bad idea, assuming they can start turning at a low voltage. But I suppose getting better fans is the real solution.

Cheers,
Ben.