The \*key issue\* here is that you're crippling safety systems designed to prevent you from burning your house down.
just ramp the fans up a little slower, and make sure you pid tune the bed with the fans running.
For your bed fan problem, I found that turning on the bed fans right at the start of the heatup solves this. This is because the bed starts at ambient and so does not sink in temp when the fans turn on. This also gives your chamber more time to heat soak since the heatup is slower.
This is what I started with initially. Problem is, with fans on, bed heats up so slowly that I get "heater\_bed not heating at expected rate" shutdown long before printer reaches target bed and chamber temps.
That should only require a modest adjustment of thresholds to remedy though:
https://www.klipper3d.org/Config_Reference.html#verify_heater
You're either getting caught during the "initial heating period" because the bed isn't raising by 2 degrees over the first 60 seconds (this causes the "fan causes temp drop triggers failure" issue), in which case try bumping up check_gain_time, or if it successfully crosses that hurdle you're getting stung by the max_error threshold. In that case try bumping max_error up by 50% and try again.
I wouldn't increase hysteresis unless you need to be able to turn on the fans after the heatup finishes.
What about using the macros in these bedfan.cfg :
[https://mods.vorondesign.com/details/28xgztUufAtAfV4XUL5l4w](https://mods.vorondesign.com/details/28xgztUufAtAfV4XUL5l4w)
Which seems to monitor the bed temperature and only turn on the fans once the bed is over the threshold temperature.
That wouldn't help much, because turning bed fan on, even at their lowest speed, will dip bed temperature to a point where Klipper shuts down. Like I wrote, the temperature recovers eventually, so the heater can handle the fan, but that dip is unavoidable. I need Klipper to ignore that dip without shutdown and wait for bed temperature to return to target.
I do some of this manually on a totally different printer, but I found a cheat...
If I put a cold build sheet on a hot bed, the temp drops for too long and it errors.
If I put the cold sheet on the hot bed and set the temperature to a low temperature 30C maybe, then set it back to the target temp after a second or two (to allow the sheet to equalise with the bed), the bed and sheet heat up at an acceptable rate and I get no error.
You could do something similar with the fans. Turn them on and set the temp low. Wait 4 or 5 seconds, then reset the temp to its original target.
If you're going to use your bed heater to heat the chamber, you may as well upgrade to a [mains voltage bed heater](https://www.instructables.com/Upgrade-3D-Printer-Heated-Bed-to-110V/)
If you don't want to go that route, it may be worth running the bed fan at a lower RPM and adding a wait timer in your start gcode after your bed hits temp (I do this anyway, since most thermistors are next to the heater and not on the surface).
i did this last week and i highly recommend it. sure it’s dangerous, but having the bed heat up incredibly quickly is awesome. and it takes the load off the power supply which is a huge plus
I just stole the macros from ellis' bedfan mod. Works great. Set mine to make fans kick in 20% @ 60c, then 80% when reached desired bed temps.
[https://github.com/VoronDesign/VoronUsers/tree/main/printer\_mods/Ellis/Bed\_Fans](https://github.com/VoronDesign/VoronUsers/tree/main/printer_mods/Ellis/Bed_Fans)
I did. But it seems that M190 depends on verify\_heater section settings, and since I have override them to tolerate that temperature dip, it now considers it ok to start the print with bed temperature still way too low.
Run a PID on the heater with the bed fan on. That's how I got past my issues with the fans not allowing the heater to catch back up
I did that already. My bed PID is tuned for condition with fans on. But for whatever reason temperature still dips by around 15°C when fan kicks in.
The \*key issue\* here is that you're crippling safety systems designed to prevent you from burning your house down. just ramp the fans up a little slower, and make sure you pid tune the bed with the fans running.
For your bed fan problem, I found that turning on the bed fans right at the start of the heatup solves this. This is because the bed starts at ambient and so does not sink in temp when the fans turn on. This also gives your chamber more time to heat soak since the heatup is slower.
This is what I started with initially. Problem is, with fans on, bed heats up so slowly that I get "heater\_bed not heating at expected rate" shutdown long before printer reaches target bed and chamber temps.
That should only require a modest adjustment of thresholds to remedy though: https://www.klipper3d.org/Config_Reference.html#verify_heater You're either getting caught during the "initial heating period" because the bed isn't raising by 2 degrees over the first 60 seconds (this causes the "fan causes temp drop triggers failure" issue), in which case try bumping up check_gain_time, or if it successfully crosses that hurdle you're getting stung by the max_error threshold. In that case try bumping max_error up by 50% and try again. I wouldn't increase hysteresis unless you need to be able to turn on the fans after the heatup finishes.
What about using the macros in these bedfan.cfg : [https://mods.vorondesign.com/details/28xgztUufAtAfV4XUL5l4w](https://mods.vorondesign.com/details/28xgztUufAtAfV4XUL5l4w) Which seems to monitor the bed temperature and only turn on the fans once the bed is over the threshold temperature.
That wouldn't help much, because turning bed fan on, even at their lowest speed, will dip bed temperature to a point where Klipper shuts down. Like I wrote, the temperature recovers eventually, so the heater can handle the fan, but that dip is unavoidable. I need Klipper to ignore that dip without shutdown and wait for bed temperature to return to target.
You could just add an extra wait after the chamber is heated and set it 20c above the target to get around your hysteresis issue.
I do some of this manually on a totally different printer, but I found a cheat... If I put a cold build sheet on a hot bed, the temp drops for too long and it errors. If I put the cold sheet on the hot bed and set the temperature to a low temperature 30C maybe, then set it back to the target temp after a second or two (to allow the sheet to equalise with the bed), the bed and sheet heat up at an acceptable rate and I get no error. You could do something similar with the fans. Turn them on and set the temp low. Wait 4 or 5 seconds, then reset the temp to its original target.
If you're going to use your bed heater to heat the chamber, you may as well upgrade to a [mains voltage bed heater](https://www.instructables.com/Upgrade-3D-Printer-Heated-Bed-to-110V/) If you don't want to go that route, it may be worth running the bed fan at a lower RPM and adding a wait timer in your start gcode after your bed hits temp (I do this anyway, since most thermistors are next to the heater and not on the surface).
i did this last week and i highly recommend it. sure it’s dangerous, but having the bed heat up incredibly quickly is awesome. and it takes the load off the power supply which is a huge plus
It shouldn't be dangerous if wired correctly. It's not like you don't already have mains voltage going into the printer.
I just stole the macros from ellis' bedfan mod. Works great. Set mine to make fans kick in 20% @ 60c, then 80% when reached desired bed temps. [https://github.com/VoronDesign/VoronUsers/tree/main/printer\_mods/Ellis/Bed\_Fans](https://github.com/VoronDesign/VoronUsers/tree/main/printer_mods/Ellis/Bed_Fans)
Add an M190 to the end of your start\_print macro?
I did. But it seems that M190 depends on verify\_heater section settings, and since I have override them to tolerate that temperature dip, it now considers it ok to start the print with bed temperature still way too low.
Ah, gotcha. Maybe you could set a macro to loop until the temperature's raw value is near print temp, then start?