Heater Control

dc42 · 19 Sept 2016, 18:20

Those results don't sound right. What M307 parameters did it return? Can you measure the resistance of the heater cartridge? Do you have any thermal insulation on your hot end?

I believe E3D changed the power of the heaters they ship from 40W to 25W some time ago.

mhackney · 19 Sept 2016, 18:25

This is a 40W cartridge that measures 3.6Ω, no insulation. Unfortunately, I did not check M307.

I just reran it after waiting for it to cool to room temperature as:
M303 H1 P0.25 S250

Temperature increased gradually (I have a screen shot) and then get this message:
Auto tune of heater 1 with P=0.25 S=250.0 cancelled because temperature limit exceeded. Use lower P or higher S in m303 command.

I did an M307 H1:
Heater 1 model: gain 862.3, time constant 296.2, dead time 6.9, max PWM 1.00, in use: yes, mode: PID
Setpoint change: P8.9, I0.03, D42.9
Load change: P8.9, I0.65, D42.9

I'll rerun the P0.2 S240 and do an M307 this time.

dc42 · 19 Sept 2016, 18:40

So that's 43W at 12.45V. Your time constant found by tuning is about double the value I get, which suggests to me that either your hot end is better insulated than mine or your hot end heatsink cooling fan is not very effective. The combination of high heater power and long time constant explains the high gain and hence the warning message.

mhackney · 19 Sept 2016, 18:47

It's a stock E3D V6 with standard cooling fan and shroud. I've measured the top of the cold zone and it is fine and I never get plugging with PLA. The parameters I use with the M301 are:

M301 H1 P20 I0.27 D100 T1.1 S1 W300 B30

(this is with 1.15-beta3) and worked fine. Hot end heated up quickly and stabilized. I have other printers I can update to the 1.15c firmware but they are Duet .85 controllers. Not sure what to do here with this one though.

I did rerun the P0.2 S240 and got the same overpower warning and this time I dd the M307:

M307 H1
Heater 1 model: gain 884.2, time constant 296.0, dead time 6.8, max PWM 1.00, in use: yes, mode: PID
Setpoint change: P8.7, I0.03, D41.8
Load change: P8.7, I0.64, D41.8

dc42 · 19 Sept 2016, 18:53

The warning is genuine then, although it may be exaggerating somewhat because it assumes that the heat loss is linear with temperature, which is not exactly true.

I suggest you plug the M307 parameters into config.g. If they don't give you good temperature control, you can put your M301 command back after the M307 if you double and halve the I and D parameters as per the 1.15 release notes.

mhackney · 19 Sept 2016, 19:04

Thanks David.

But this begs the question - what's the "right" thing to do from a heater perspective? Is this legitimately a safety concern and if so, what should be done to rectify it? Is this unique to my E3D V6 or all of them?

mhackney · 19 Sept 2016, 19:18

Ok, I plugged the parameters into M307:
M307 H1 A884.2 C296.0 D6.8 B0 S0.8

I did leave S0.8 for no good reason. It is working perfectly - climbs steadily up to my target (190°C) and then levels with no overshooting and stabilizes much faster with less than +/-.1°C variation. Much better than what I had before.

dc42 · 19 Sept 2016, 19:18

@mhackney:

Thanks David.

But this begs the question - what's the "right" thing to do from a heater perspective? Is this legitimately a safety concern and if so, what should be done to rectify it? Is this unique to my E3D V6 or all of them?

You might want to consider replacing your 40W heater cartridge by a 25W one, which I understand is what E3D ships as standard these days. Otherwise you might suffer a heater block meltdown if the heater ever got stuck at full power.

elmoret · 19 Sept 2016, 19:25

30w is now standard, which tops out at ~330C without heater block insulation or a fan blowing on the heater block.

40w will get hot enough to melt the aluminum in the event of a firmware/FET failure.

mhackney · 19 Sept 2016, 19:28

Ok, this is good to know! I will check and update the cartridges in all of my printers. No need playing with fire!