Heater fault on heated bed because it's rising to slow.

Exerqtor

I've suddenly started getting heater faults on the bed heater while heating up before a print because it's allegedly heating up slower than what RRF wants it to.

It's a PID tuned 230v 750w 300x300mm silicone heater attached to a 8mm thick 350x350mm cast aluminum bed, switched with a SSR.
config-override.g:

M307 H0 B0 R0.902 C267.4 D3.56 S1.00 V12.5 ; Bed heater tuned for 80C with 230v 750w heater

When I just tried heating the bed from room temp (22c ish) to 85c I got three faults that i had to reset before i got it up to the requested 85c.

The faults were:

26.11.2021, 10:13:01	Error: Heater 0 fault: at 83.5°C temperature is rising at 0.2°C/sec, well below the expected 0.5°C/sec
26.11.2021, 10:12:16	Error: Heater 0 fault: at 75.0°C temperature is rising at 0.3°C/sec, well below the expected 0.7°C/sec
26.11.2021, 10:11:13	Error: Heater 0 fault: at 63.6°C temperature is rising at 0.4°C/sec, well below the expected 0.7°C/sec
26.11.2021, 10:09:28	M32 "0:/gcodes/MGN12_z_carriage_rear_3hole+counterweight_0.2mm_CPE_3h12m.gcode"
File 0:/gcodes/MGN12_z_carriage_rear_3hole+counterweight_0.2mm_CPE_3h12m.gcode selected for printing

I was holding an eye with it on the Paneldue all the time, and it's almost like the heater refresh stutters for half a second or so (for both bed and hotend) right before the faults get thrown.

Should i try to re-tune the heater? Or is it something else i should do?

Edit:
Oh yeah and the bed related stuff from config.g:

; Bed heater
M308 S0 P"bedtemp" Y"thermistor" T104400 B4138 A"Bed"	; configure sensor 0 as thermistor on pin bedtemp
M950 H0 C"bedheat" T0					; create bed heater output on bedheat and map it to sensor 0
M307 H0 B0 S1.00					; disable bang-bang mode for the bed heater and set PWM limit
M140 H0							; map heated bed to heater 0
M143 H0 S110						; set temperature limit for heater 0 to 110C
M143 H0 A2 C0 S110					; make sure bed heater stays below 110°C
M143 H0 A1 C0 S125					; make sure bed heater shuts down at 125°C

cosmowave

@exerqtor Eventually you should adjust the heating rate with the M307 R paramenter...

Exerqtor

@cosmowave

Thanks for the tip, I'll try lowering it to 0.8 and see if that's enough.

Gixxerfast

I had a thermistor fail in my Keenovo heater that gave me heater errors.

How do the temp curve in DWC look like, smooth or uneven?

Also, take a look at your temp fuse if you have a chinese lower temp variant

Exerqtor

@gixxerfast

That's what's so strange because everything looks (and "feels" fine) even when it throw's the fault. Curve is all good and it's heating fast. and holds temp steady once it reaches it no matter what the temp should be.

I'm about to do a print with the heating rate set to 0.800, so fingers crossed that will be help.

Edit:

Turns out 0.800 wasn't enough, it helped but it still threw an error (un in the 70c range this thime), adjusted it to 0.750, and it did the rest of the heating without throwing a tantrum.

Phaedrux

Where is the bed thermistor attached? on the heater itself or in the plate to be heated?

Exerqtor

@phaedrux
It's attached straight on the silicone heater from factory.

Phaedrux

I'm surprised it's taking longer to heat up in that case. Is there an air bulge or something keeping the thermistor out of contact with the heater itself? I'd be tempted to try with a different thermistor to try and rule that out, even if only temporarily.

Alex.cr

@Exerqtor
I have to ask the simple question because I didn’t see an answer for it yet. Do you have an M501 at the end of you config.g ?

config-override.g:

M307 H0 B0 R0.902 C267.4 D3.56 S1.00 V12.5 ; Bed heater tuned for 80C with 230v 750w heater

After performing a reboot you can try sending an M307 H0 to verify the correct Param are set for the heated bed?

rjenkinsgb

You appear to be using the default PWM frequency, but with an SSR?

That is unlikely to work well, as the PWM will interact with the AC power frequency, which is all the SSR can switch at.

That could be causing the "stutter" as well.

Try setting the PWM frequency to eg. 5Hz or enabling bang-bang mode instead?

Exerqtor

@phaedrux said in Heater fault on heated bed because it's rising to slow.:

I'm surprised it's taking longer to heat up in that case. Is there an air bulge or something keeping the thermistor out of contact with the heater itself? I'd be tempted to try with a different thermistor to try and rule that out, even if only temporarily.

Well adjusting it the R value to 0.75 seemed to fix the issue. S it looks like it just werent able to heat up as fast as result of the tuning wanted it too.
I haven't got the feeling that it was/is an physical problem at all.

@alex-cr said in Heater fault on heated bed because it's rising to slow.:

@Exerqtor
I have to ask the simple question because I didn’t see an answer for it yet. Do you have an M501 at the end of you config.g ?
config-override.g:
M307 H0 B0 R0.902 C267.4 D3.56 S1.00 V12.5 ; Bed heater tuned for 80C with 230v 750w heater
After performing a reboot you can try sending an M307 H0 to verify the correct Param are set for the heated bed?

Yeah all that's ok, M501 is the secound last line (followed by T0) in the config.g, so it's applying the parameters correctly. It was just expecting it to heat up faster than what it actually was capable off.

Phaedrux

Adding a Q10 to your M950 for the bed might be a good idea

This post is deleted!

Exerqtor

Sure I can add a Q to the M950, but what should i go for? 5,10 or 50? Also i didn't see any mention of the need oe posible need for it when running a SSR to regulate mains voltage anywhere in the documentation Or have I missed it somewhere?

Phaedrux

@exerqtor https://duet3d.dozuki.com/Wiki/Choosing_a_bed_heater#Section_RepRapFirmware_3_x

rjenkinsgb

@exerqtor said in Heater fault on heated bed because it's rising to slow.:

Sure I can add a Q to the M950, but what should i go for? 5,10 or 50?

No more than 10.

An AC SSR is normally "zero voltage switching" - at the start of each AC half cycle, it either switches on, or not. It does not change state during the half cycle.

That means you have 100 or 120 (for 50/60 Hz) on or off "timeslots" each second.
Running at or above the power frequency will give unpredictable results, more luck than anything if it works anywhere near smoothly.

The control frequency needs to be low enough to give a reasonable range of control, different power levels, within each PWM cycle.
10Hz would give roughly 10% increments at 50Hz or 8% increments at 60Hz.

5Hz would give nearer 5% / 4% increments, so slightly smoother control at the cost of fractionally slower response - but with a big heated bed that's not really an issue.

You could try both & see which gives best response. It won't hurt anything, just re-tune at each setting.
Save both tuning result lines in case you want to change in the future.

Exerqtor

@phaedrux said in Heater fault on heated bed because it's rising to slow.:

@exerqtor https://duet3d.dozuki.com/Wiki/Choosing_a_bed_heater#Section_RepRapFirmware_3_x

Haven't looked at that specific page in ages! Would have been really nice with a "mentioned in/ referanced in" ish thing at the bottom of each gcode specific dozuki page that links to every other documents that contain or mention that specific code. Kinda like the way wikipedia is settup with referance links in the bottom (yeah i know that's alot of work to setup, but if it was a quick'n easy interface for setting up referance links for logged in users i'm pretty sure it would get done relatively quickly).

BUT, now i know

@rjenkinsgb said in Heater fault on heated bed because it's rising to slow.:

@exerqtor said in Heater fault on heated bed because it's rising to slow.:

Sure I can add a Q to the M950, but what should i go for? 5,10 or 50?

No more than 10.

An AC SSR is normally "zero voltage switching" - at the start of each AC half cycle, it either switches on, or not. It does not change state during the half cycle.

That means you have 100 or 120 (for 50/60 Hz) on or off "timeslots" each second.
Running at or above the power frequency will give unpredictable results, more luck than anything if it works anywhere near smoothly.

The control frequency needs to be low enough to give a reasonable range of control, different power levels, within each PWM cycle.
10Hz would give roughly 10% increments at 50Hz or 8% increments at 60Hz.

5Hz would give nearer 5% / 4% increments, so slightly smoother control at the cost of fractionally slower response - but with a big heated bed that's not really an issue.

You could try both & see which gives best response. It won't hurt anything, just re-tune at each setting.
Save both tuning result lines in case you want to change in the future.

Yeah it's an original Omron "Zero-crossing" SSR I'm using, and were on 230V/50Hz here in Norway so I'll try with 5Hz in the M950 and then do a new tune.

Again, thanks for the help and enlightenment guys

Edit:
Ran a new tuning now with the PWM set to 5Hz, and ended with "M307 H0 B0 R0.955 C228.2 D3.40 S1.00 V12.5", an even higher heating rate.
Waiting for it to settle down to room temp before I try running a preheat with those parameters to see how it behaves.

Exerqtor

@exerqtor

Didn't have time to test yesterday, so i just tried a heatup and :

Error: Heater 0 fault: at 64.9°C temperature is rising at 0.4°C/sec, well below the expected 0.7°C/sec

So i get the feeling the tuning outputs a higher than realistic heating rate to be honest.

pfn

@arnold_r_clark

I'm also seeing similar behavior since updating to 3.4.0b6 (from 3.3.0)

My bed heater faults very often while initially warming up. And I can also clear the fault and continue heating, but very annoying.

Re-running PID tuning did not improve the situation.

SIam

Hi,

Try to use the half of the computed R value from the PID Tuning, This is how it works with my printer

https://forum.duet3d.com/topic/25321/bed-heater-fault-3-4-b5

Heater fault on heated bed because it's rising to slow.

Robert J.

Robert J.