RRF3.2 M303 Warning: heater behaviour not consistent

[fractalengineer]

Hi,

I just updated my Duet 3 to RRF 3.2 and while the next PID tuning for my hotend worked well, the bed returned this warning message and I'm not sure whether to use the M307 or not?

Setup is a 750W AC keenovo bed with SSR. 5mm alu plate

What does that warning means?

Thanks!

1/26/2021, 12:16:40 PM	Edit the M307 H0 command in config.g to match this. Omit the V parameter if the heater is not powered from VIN.
1/26/2021, 12:16:40 PM	Auto tuning heater 0 completed after 7 idle and 25 tuning cycles in 4595 seconds. This heater needs the following M307 command:
 M307 H0 R0.498 C698.6 D5.71 S1.00 V29.4
1/26/2021, 12:16:40 PM	Warning: heater behaviour was not consistent during tuning
1/26/2021, 11:14:52 AM	Auto tune starting phase 3, fan off
1/26/2021, 11:01:30 AM	Auto tune starting phase 2, heater settling
1/26/2021, 11:00:09 AM	Auto tune starting phase 1, heater on
1/26/2021, 11:00:04 AM	M303 H0 S55
Auto tuning heater 0 using target temperature 55.0°C and PWM 1.00 - do not leave printer unattended

[Phaedrux]

This warning seems to occur when a powerful heater is used with a large bed and the thermistor is in direct contact with the heater rather than inside of the plate.

It's possible to add a second heater embedded in the plate for PID tunind and control and leave the thermistor connected to the heater pad itself as an overtemp warning monitor.

[matt3o]

the returned M307 won't probably work, at least it didn't for me and I had to manually tune it to avoid heater errors. I'll have to find a way to embed a thermistor into the bed itself instead of relying on the one with the heater.

[fractalengineer]

ah damn that's embarassing; I'm using the built-in thermistor on the back of my keenovo.

I'm glad I can keep the previous M307 from earlier version of RRF; it's working just fine

How would I go about tuning it again today? Can I use the old protocol?

[matt3o]

I ran the tuning as normal and used the returned values as baseline.

I slightly lowered the heating rate (R) so RRF thinks it's less powerful, and increased a little C and D.

This was what tuning reported M307 H0 R0.729 C638.9 D4.16 S1.00 this is what actually works M307 H0 R0.600 C700 D6 S1.00

Remember to remove the V parameter as you are using an SSR also remember to set Q10 to your M950 in the bed heater definition if you haven't already

[fractalengineer]

@matt3o interesting, that's a bit ghetto but smart move lol

I got jobs to do so I'll keep the old bed tuning for now.

What do you mean about setting a pwm freq of 10 for the bed heater; is it to be easier on the SSR?

[matt3o]

@fractalengineer said in RRF3.2 M303 Warning: heater behaviour not consistent:

What do you mean about setting a pwm freq of 10 for the bed heater; is it to be easier on the SSR?

RRF3 does not automatically lower PWM depending on the output. See here

that's a bit ghetto

oh yeah man, Ghetto should be my printer's name by now.