Hotend over powered warning

zapta

I run a PID autotune and got a warning that the hotend heater is over powered. This is an E3D Titan style hotend with 40W/24V heater (red wires).

8:05:38 PMM307 H1
Heater 1 model: gain 644.5, time constant 206.5, dead time 4.5, max PWM 1.00, calibration voltage 24.1, mode PID, inverted no, frequency default
Computed PID parameters for setpoint change: P12.6, I0.412, D40.0
Computed PID parameters for load change: P12.

8:04:14 PMWarning: Heater 1 appears to be over-powered. If left on at full power, its temperature is predicted to reach 669C.
Auto tune heater 1 completed in 288 sec
Use M307 H1 to see the result, or M500 to save the result in config-override.g

This made me to wonder about these questions:

Should I switch to lower power heater? E.g. the blue wires 25W/24V?
Is it common to add a thermal fuse to the hotend?
I didn't get a max temp estimation for the bed but wonder what it is. Anyway to estimate from the PID results?

7:47:37 PMM307 H0
Heater 0 model: gain 64.1, time constant 277.0, dead time 3.2, max PWM 1.00, calibration voltage 24.2, mode PID, inverted no, frequency default
Computed PID parameters for setpoint change: P239.7, I8.026, D540.3
Computed PID parameters for load change: P23

Thanks,
Z.

Phaedrux

It's up to you if you want to switch to a lower powered heater. The 40w is probably going to be overkill for most things. The warning is telling you how hot the firmware predicts the heater could get in a runaway situation. You could add a thermal fuse, but I think it may be hard to find one that is that high temp that is both cheap and able to withstand so many heat cool cycles at such high temps.

Inherent safety is better than reactive safety. So a lower powered heater that can't get hot enough to melt aluminum is safer than a heater that has a cutout to hopefully prevent it from melting aluminum.

If you didn't get a warning for the bed, that would indicate that it's not possible for it to get hot enough to damage itself so should be ok. I could be wrong though. I have a 600w silicone heat bed and I do get a warning. What type of bed heater is it?

dc42

To estimate the maximum temperature of the bed, add the gain value to ambient temperature.

zapta

@dc42 said in Hotend over powered warning:

To estimate the maximum temperature of the bed, add the gain value to ambient temperature.

Thanks, that's very useful. 64+25 gives about 90C which I like. (I print PLA and PETG at 60C and the magnetic bed will get damaged going much above it).

As for the extruder, if I want to find the max temp if I will reduce heater from 40W to 25W cartridge, is it reasonable to run the command [M303 H1 P0.79 S230] and use (gain+25) as an estimation for max temp?

(0.79 = sqrt(25/40), which I guess is the right duty cycle (?))

dc42

@zapta said in Hotend over powered warning:

@dc42 said in Hotend over powered warning:

To estimate the maximum temperature of the bed, add the gain value to ambient temperature.

Thanks, that's very useful. 64+25 gives about 90C which I like. (I print PLA and PETG at 60C and the magnetic bed will get damaged going much above it).

As for the extruder, if I want to find the max temp if I will reduce heater from 40W to 25W cartridge, is it reasonable to run the command [M303 H1 P0.79 S230] and use (gain+25) as an estimation for max temp?

(0.79 = sqrt(25/40), which I guess is the right duty cycle (?))

I don't think that will work, because the gain is calculated at full power even if you use a lower limit. But as a very rough guide, gain is proportional to heater power. So a 25W heater should still allow you to reach well over 300C, unless you are using a very large nozzle (in which case higher power is needed when extruding fast).