Disabling Thermostatic Fan on Start-Up

deckingman

@Dizzwold I vaguely remember having a conversation with DC about this but it was a long time ago. IIRC, it has to do with if an emergency shut down or some such is used, then the board is restarted, the fans come on immediately to start cooling the hot end rather than wait for the board to fully boot. So the default behaviour on start up is turn on the fans, then read and act on the contents of config.g. I could be wrong on that - it was a long time ago.

Dizzwold

@deckingman @jens55

Hi Guys,

I'll try to explain this a little more.

I have a 24v fan that i wish to use as a Temperature related chamber extraction fan linked to an individual temperature sensor, NTC104 thermistor.

I'd like the fan to run proportionally from 0 to 100% to the temperature range of 40-80˚C.

For testing I've linked the fan to the hotend H1, in thermostatic mode and disabled the blip time (B0.0). This works fine, but I don't want the extractor fan to run at 100% when the printer is switched on;

; Heaters
M308 S1 P"121.temp0" Y"thermistor" T100000 B4138       ; configure sensor 1 as thermistor on pin temp1
M950 H1 C"121.out0" T1                                 ; create nozzle heater output on out1 and map it to sensor 1
M307 H1 R2.498 K0.275:0.349 D6.79 E1.35 S1.00 B0 V24.0  ; disable bang-bang mode for heater  and set PWM limit
M143 H1 S280                                       ; set temperature limit for heater 1 to 280C

; Fans
M950 F1 C"121.out1" Q500                               ; create fan 1 on pin out5 and set its frequency
M106 P1 C"Extruder Cooling" S1 H1 T45              ; set fan 1 name and value. Thermostatic control is turned on
M950 F2 C"out1" Q250						;create Extractor fan on out1
M106 P2 C"Extractor Fan" T40:80 H1 B0.0

So basically can I use the fan in Non Thermostatic mode and still use the proportional settings, therefore not having the sudden burst of the fan running at 100% when powered-up?

Second question is, how do I link this fan to a separate thermistor without a heater?
Do I have to have a virtual heater using P(101,102,103), as the documents are a bit misleading starting with using M305, now replaced by M308, but then the notes in M308 state very little regarding virtual heaters, so you go back and read M305 notes again?
This is what I'm planning on adding for the separate thermistor for the extraction fan;

; Sensors
M308 S2 P"temp1" Y"thermistor" A"Chamber Temp"T100000 B4138

Can I use S2 (extractor fan), from the last snippet above in M950, as I can't use S2after M106 as this is would be the fan speed.
M950 F2 C"out1" Q250 S2

I'd be grateful for your ideas and solutions .

Dizzwold.

apak

@Dizzwold why don´t you set up a range of operation

M106 P2 H2 L.3 B.5 X1 T40:65

Will start above 40ºC at 30% of the fan increasing to 100% proportionally until 65ºC is reached

B is 50% jump start

Just play with the T values as you wish

deckingman

@Dizzwold With regard to your question 2, you don't need to create a virtual heater. It's slightly confusing but the "H" parameter in M106 refers to a sensor created by M308, not a heater. So just wire your thermistor to a temperature input, create your sensor using M308 then configure the fan using M106 to run thermostatically using that sensor.

With regard to you first question, I've already answered it as best I can. I believe (from a conversation I had with DC some time ago) the reason is that on first boot, the fans will run at full power in case the power was cycled due to a print failure but to prevent the hot end blocking due to heat creep, it needs the fan turning on as soon as possible after power is restored. I don't know for sure but I'd assume that it applies to all fan ports regardless of whether anything is connected to them or not. So it happens before config.g is read in and acted on. Therefore, it doesn't matter what you put in config.g - it won't prevent that initial short burst. Having said that, it should only be for a few seconds which I wouldn't have thought would be any cause for concern. Or are you saying that the fan runs for a considerable time when power is first applied?

Dizzwold

@deckingman @jens55 @apak

Hi Guy's,

Thank you for your replies, I'm grateful for your help and advice.

Yeah, it is a bit confusing in the documents. Thank you for pointing out that Hx created in M308 will be the thermistor in my case.

With Q1, I'm fully aware of the safety reasons behind the initial burst on start-up. I only wanted to know if the initial burst cold be disabled or not, or if there was a way to kind of replicating a thermostatic fan by other means where the start-up burst could be omitted.

Thank you for reiterating the safety behind the initial burst on star-up as others may not be so aware of this.

I'll tinker around some more with the example from @apak, not to dissimilar to what I had, but with now understanding that Hx created in M106 will be the thermistor, it make sense.

Does anyone know why there is the Blip Number (B.5). Just having a stab in the dark, is it to prevent fan/spindle stall?

Thank you for your help.

Dizzwold.

deckingman

@Dizzwold said in Disabling Thermostatic Fan on Start-Up:

...............Does anyone know why there is the Blip Number (B.5). Just having a stab in the dark, is it to prevent fan/spindle stall?

No, it's just a configurable number to give a fan an initial kick. If one tried to start a fan (or any motor) at a low PWM of (say) 10% or less, the chances are high that it might not turn at all due to static friction and/or initial inertia. But if you give it a kick at high power to get it turning, then you can use a low PWM and it'll keep it turning. You might have noticed something similar when using variable speed power tools with a big cutter that you want to run at low speed. You gently squeeze the trigger but nothing much happens apart from a bit of a buzzing noise so you squeeze a bit harder and eventually it bursts into life. Then one it's turning, you back off the trigger to where you originally had it set and it'll continue to turn quite happily.

engikeneer

@Dizzwold I think the blip might be a hardware thing on all fan outputs rather than something configurable.
Simplest way to check is to pull the SD card out and then turn on the printer. That way no config file is run and you'll see what the hardware will do on its own.

I'd say your two options might be to either configure the fan right at the start of your config so it gets configured first and the blip is shortest, or use a spare heater output to drive it instead (assuming it runs from Vin) as they won't be wired to blip on

OwenD

@Dizzwold
I suppose if it is critical that the fan not run during startup you could power the fan by running one wire through a normally open relay.
Then if you configure the relay and close it at the end of your config.g

Dizzwold

@OwenD @apak @deckingman @engikeneer @jens55

Is there a way to create a control for the extractor fan in DWC?

Phaedrux

@Dizzwold Something like this?
https://forum.duet3d.com/topic/22776/btncmd-dwc-plugin-customise-dwc-v01-02-07-17-09-23

fcwilt

@Dizzwold said in Disabling Thermostatic Fan on Start-Up:

FIRMWARE_NAME: RepRapFirmware for Duet 3 MB6HC FIRMWARE_VERSION: 3.4.6 ELECTRONICS: Duet 3 MB6HC v1.01 FIRMWARE_DATE: 2023-07-21 14:11:38

Hi All,

Is there a way to disable a fan connected as a thermostatic fan on start-up?

I know this sounds somewhat counter intuitive, but the idea if to have an enclosure fan/extractor fan (thermostatically controlled), to keep the enclosure at a set temperature?

Or would it just be simpler/safer to buy a separate temperature controller?

Dizzwold.

That short burst is not going to affect the temperature of anything the fan might by linked to.

Go have a nice dinner and enjoy the evening.

Frederick

Dizzwold

@fcwilt ,

Mmm, Lamb Tagine

@Phaedrux ,

Thank you for that. I'll read up on this.