Heater fault

ianborg

duet3d v2 latest firmware
I have a 300x300 aluminum bed with magnets and magnetic build plate.
heating source is 750w mains (120v) silicon heating pad
hooked to a uxcell ASH-25DA Solid State Relay 4-32VDC to 24-480VAC 25A Single Phase SSR DC to AC Relay
I get a heater fault almost every time i print. I have to heat up the bed to the desired temp and once it reaches, it stays, but if i start a print and the bed isn't heated, i get a fault.
"Heater 0 fault: temperature rising too slowly: expected 0.43°C/sec measured 0.12°C/sec"
I have tried PID auto tune many times and even when i plug the suggested numbers in, i still have issues.
looking for suggestions?
current settings.

; Heaters
M308 S0 P"bed_temp" Y"thermistor" T100000 B3950 C0 R4700	; define bed temperature sensor                    
M950 H0 C"bed_heat" T0
M140 H0
M143 H0 S120 ; set temperature limit for heater 0 to 120C
M308 S1 P"e0_temp" Y"thermistor" T100000 B4725 C7.060000e-8	; define extruder temperature sensor
M950 H1 C"e0_heat" T1 ; heater 1 uses the e0_heat pin and sensor 1
M143 H1 S300                           ; set temperature limit for heater 1 to 280C
M307 H0 R0.797 K0.250:0.000 D7.14 E1.35 S1.00 B0
M307 H1 R3.615 K0.413:0.000 D2.40 E1.35 S1.00 B0 V24.6

jens55

@ianborg, I have similar issues with a nozzle heater. It generally boils down to poor connections either at the heater end, temperature sender end , at the controller end (rare) of either or, as in my case, a plug/socket connection in the line (so I can swap out either without a major effort).
Looking at the temperature curve can usually give you a good hint on where the fault lies. The bed can't change temperature fast so if you see a fast temperature change the issue is in the temperature sensing circuit. If it is a slooow temperature change then it's likely to be the heater.
Last but not least, at least in my case, there is a good chance the sensor itself is faulty or getting towards it's end of life.
Good luck!

ianborg

@jens55 appreciate the reply. In my case, if I heat the bed before i print. it's fine
so that would rule out connector issues. once it's up to temp, it stays there until the print is over. that will rule out the thermostat. I think it's my PID settings are not right, I'm just not sure what i need to tweak, I've ran auto tune many times, but the values are fairly similar each time, yet i get the heating too slowly message.

jens55

@ianborg I would look into possible interference somewhere but I can't suggest where to start looking.
Alternatively, as a band-aid, set your printer up to only start heating the nozzle when the bed is at temperature.

gloomyandy

@ianborg That seems very strange. I guess the obvious question is what is different between heating the bed ahead of time v during printing? As previously mentioned a possibility is some form of electrical interference, the other that I can think of is fans? When you run a print do you have fans running and are they blowing over the bed and cooling it? What sort of fan set up do you have? There are options to PID tune the bed with fans running did you try doing that? What happens if before heating the bed at the start of the print you move the bed away from the nozzle? Does that help at all?

ianborg

@gloomyandy appreciate the reply. No fans running during warm up.
the bed does heat up just fine and holds the temp during prints perfectly.
i just get a fault that it's taking too long to heat up, when I searched the forums, I see a few other folks
with the same / similar setup (750w heaters) also mention slow heating or issues. I don't have any issues waiting as it doesn't take all that long. my problem is duet is generating a fault and saying it's rising too slowly. I would like to make that go away, if it take 5 minutes then fine. i just don't want the fault, i clear it. heat the bed up and start the print and it's fine from there.

ianborg

Looking through more post and docs, i think M570 is going to be my friend.
am going to try that out

ianborg

hey what do you know.. no faults after adding m570 command, default i think was 3 seconds, i set to 10 and number of times set to 10 and it's off an printing.
it took 3 minutes to go from 20c to 90c, as i watched, it appeared to go slower as it approached set temp. so I'm guessing I can tune it better. but 3 minute is fine for me to heat up.

droftarts

@ianborg I expect there's a bit of latency between the heater starting to heat, and the temperature sensor sensing any change, most likely because of the position of the temperature sensor relative to the heater is not ideal. When you start heating, does it initially take a while to start heating, and the initial heating is a curve?

Most likely using M570 as you have is probably the easiest way around it. You can calculate the heater parameters yourself, see https://docs.duet3d.com/en/User_manual/Connecting_hardware/Heaters_tuning#setting-the-model-parameters-manually, and also adjust the heating parameters, see https://docs.duet3d.com/en/User_manual/Connecting_hardware/Heaters_tuning#manual-adjustments-to-the-heater-model-parameters

Ian

ianborg

@droftarts

got me again today, you can see it was almost to 90c
then
Heater 0 fault: temperature rising too slowly: expected 0.40°C/sec measured 0.12°C/sec
I set my m570 more aggressive.

I don't think 3 minutes to 90c is long to wait at all. sure I'd love it faster, but there are limits to how fast you can heat something up.

ianborg

This post is deleted!

ianborg

M307 H0 R1.0 K0.250:0.000 D5 E1.35 S1.00 B0
been trial and erroring this.. that setup seems to heat up fast and not give a fault.

droftarts

@ianborg From the heater curve on the graph you posted, it does look like the heater is getting close to the maximum heat it can achieve. Controlling it at this point does get a bit squirrelly, because the heating rate isn't what is expected. Not much you can do about that, apart from what you've already done, unfortunately. Did you tune it at 90C with M303, or lower?

Ian

troydeming

@droftarts

I just jumped in to express the same exact problem. Just got my printer back up again after along break. Ill try your solution and see how it works for me.

troydeming

@troydeming
So I got home today and did the PID autotune and it is running perfectly now. Happy Camper am I