Hot-end heating fault

[ssrpp]

Hi

I have a problem with my hot-end heater behavior, it occurs when printing at higher speeds but I can easily force the fault manually.

To reproduce this I start a print with hot-end at 200 degrees first layer.
Subsequent layers are at 180 degrees.
when back down to 180 if I manually change the hot-end temp back up to 200 degrees the fault occurs.

Observing the temperature rising, it rises rapidly to approx 196 then slows down so much that the fault occurs.

I have tuned the hotend with only:

M303 H1 S220, and saved with M500. I did get the "massively overpowered" warning.

This is a 24v system, 24v heater, E3D V6 Volcano, system firmware is:

Firmware Name: RepRapFirmware for Duet WiFi
Firmware Electronics: Duet WiFi 1.0
Firmware Version: 1.20alpha7 (2017-09-24)
WiFi Server Version: 1.19
Web Interface Version: 1.19.2

config.g
<snip>M307 H1 A561.3 C310.6 D4.3 S1.00 B0
<snip>override
<snip>; Heater model parameters
M307 H0 A111.4 C195.8 D1.6 S1.00 B0
M307 H1 A561.3 C310.6 D4.3 S1.00 B0
M307 H2 A250.0 C140.0 D5.5 S1.00 B0
…...
<snip>Any idea why this is happening?</snip></snip></snip></snip>

[dc42]

Which particular heating fault message did you get, and which firmware version are you running?

[ssrpp]

Hi
Firmware Version: 1.20alpha7 (2017-09-24)

11:00:54 AMWarning: Tool 0 was not driven because its heater temperatures were not high enough or it has a heater fault
11:00:50 AMError: Heating fault on heater 1, temperature rising much more slowly than the expected 0.3°C/sec
Warning: Tool 0 was not driven because its heater temperatures were not high enough or it has a heater fault

This is taken from web interface, the error on the LCD actually states 0.2°C/sec not 0.3°C/sec oddly.

Thanks

[deckingman]

From the the gain A at 671 or 561 in your config.g it looks like you have a heater in the order of 80 Watts or so which is massively over powered and IMO dangerous. The most likely cause is that it's a 12V heater on a 24V system. The PID auto tune has done it's best to tame it but you really need to sort that out. A work around might be to run auto tune with 50% PWM (S0.5) but if it is a 12V heater, that's still dangerous and you should really fit a 24V one.

[ssrpp]

671 in config.g is incorrect its actually the same as in override now and was last tested with this value.

The heater is 40w 24v sourced from ooznest, or supposed to be!

The heater resistance is 20.2 ohms

At 24V its 30watts, if this method of calculation is accurate
Voltage (V)24 Volts (V)
Current (I)1.18812
Resistance (R)20.2
Power (P)28.51485 Watts (W)

At 12v, thats only 7watts
Voltage (V)12Volts (V)
Current (I)0.59406
Resistance (R)20.2
Power (P) 7.12871Watts (W)

My logic was this.
The heater heats the hot-end efficiently at a rate of 1 - 1.3 degrees per second.
While printing when the heater is close to temperature is slows down to avoid over temperature (I don't know how the firmware does this).
The rate of heat dissipation then becomes greater than the power applied or at least very borderline.
As a result the firmware, which expects or requires a temperature increase rate of at least 0.3 degrees per second reports a fault and the print process halts.
I also noted that the LCD and the web interface report a different degree per second value which is possibly relevant.

If this logic is correct, if I slow dowsn the print and reduce the rate of heat dissipation (less filament being extruded) then I suspect the
print wont fail and the hot-end will reach its required temperature.

[deckingman]

The gain you are showing is indicative of a vastly over powered heater and in your OP you said that you got an error message to that effect. A 30W heater would not normally give that result. I've only ever seen it when I used an 80 Watt heater, So something is wrong. Are your thermistor settings (M305) correct?

When you tune the heater, you are effectively calculating the PID parameters for that particular heater. These are what control the rate of heating, not the firmware as such. So yes, the PID control will attempt to heat as fast as possible but when it approaches the set point, the rate of heating will slow down so that it doesn't overshoot.

Suggest you check the thermistor settings and make sure that they match the thermistor that you are actually using and also to make sure that the temperature readings are correct. Then re-tune the heater.

Are you using a silicone sock? That may account for it although I wouldn't have thought that it would have made as great a difference as you are seeing. At typical gain value would be in the order of around 350 deg C for a heater that is matched to the hot end. Yours is 560.

The only other thing you could try is to re-tune the heater using a PWM value of 0.6 or so. That's the P parameter. So something like M303 H1 P0.6 S240. However, this is only usually necessary when you try to use a particularly powerful heater.

[ssrpp]

Im running PT100's on bed and hotend

; PT100 Sensors
M305 P0 X200
M305 P1 X201

Ill run the M303 you suggested and see what results I get.

[ssrpp]

That didnt go so well,

Auto tune cancelled because target temperature was not reached

[deckingman]

@ssrpp:

That didnt go so well,

Auto tune cancelled because target temperature was not reached

…......which indicates it's under powered at 0.6 PWM! There is something very odd going on here. Not sure what to suggest next.

[ssrpp]

Hi, Just ran again at 0.8, ran sucessfully, no warnings. I tried to force error on temp increase and was unable to. Makes me think that just my bad calibration skills!

5:41:20 PMM307 H1
Heater 1 model: gain 384.2, time constant 279.9, dead time 2.8, max PWM 0.80, mode: PID
Computed PID parameters for setpoint change: P46.3, I0.166, D91.0
Computed PID parameters for load change: P46.3, I4.581, D91.0
5:39:30 PMAuto tune heater 1 completed in 510 sec
Use M307 H1 to see the result, or M500 to save the result in config-override.g
5:35:10 PMAuto tune phase 3, peak temperature was 241.8

[dc42]

It's common to get the "heater over powered" warning with E3D hot ends since they started including silicone socks with them.

The expected rate of temperature increase depends on the actual temperature. What I suspect is that you're print cooling fan is cooling the heater block too much. Try to direct the print cooling fan air at the print, not at the heater block. If all sales fails you can do the heater tuning with the print cooling fan turned on, but then you will probably get some temperature overshoot during initial heating.