3.3b2: Spurious heater faults with new-style PID tuning

oliof

I have recently switched out my heater/hotend combo to a maxiwatt heater, and was able to successfully PID tune it with 3.3b1. The result of that PID tune is stored in config-override.g, which I load at the end of my config.g

This line was stored by issuing M500 after running M303 T0 S280; I did not manually edit it:

M307 H1 R5.048 C215.700:111.100 D3.90 S1.00 V23.1 B0

After upgrading to 3.3b2, I got spurious heater faults during heat-up phase. Since I disable bang-bang control in my config.g, I am using the PID defaults from Configuration.h as seen by a live query of M307:

M307 H1
Heater 1 model: heating rate 2.429, cooling time constant 140.0, dead time 5.50, max PWM 1.00, calibration voltage 0.0, mode PID
Computed PID parameters: setpoint change: P13.4, I0.482, D51.4, load change: P13.4, I0.949, D51.4

With those values, I do not get heater faults, and can print successfully, even though the maxiwatt is a 50W 24V heating element.

This is on a 6HC board with an 1LC toolboard in SBC mode, running 3.3b2 installed from the debian packages.

koaldesigns

Hello there,
I actually ran into this issue today and managed to fix it. Because it's a larger wattage hotend you have to change the auto PID tune parameters. I used a supervolcano 70-80W and used my auto-tuning as M303 H1 P.6 (the P parameter lowers the PWM signal so it heats up slower during the tune I believe) and it worked well. You may be able to increase the P value to something like .7 or .8 too.

It would be something like:
M303 H1 P.6 or M303 T0 P.6

oliof

Hi, thanks for the suggestion. I think PWM reduces the heating power overall, so I am not keen on throwing away the potential.

koaldesigns

I understand what you mean, I think the problem with the larger hotends is that the thermal mass is larger so there is a bigger delay to the heating so you get the heater error. If there was a way to add some form of time delay after heating starts until the safety mechanism kicks in, it would be possible to fix it.

From my experience, the error happens when the hotend is just starting to heat up (around 30-40C) but after that I do not get the errors (by manually bypassing them)

oliof

It's a new error in 3.3b2 -- it worked fine in 3.3b1. And the maxiwatt is very compact and heats up fast, it's not like there was a plateau.

I just started a longer print, but after that finishes, I can try again and post the temp graph that shows the heatup is not plateau-ing. I also don't get the usual error message about the heating being too slow or anything, just straight heater fault.