PID Bed Tuning Over-power Warning

What is the relevance of the over-power warning during PID tuning?

I have a 400mm x 400mm x 6.35mm MIC-6 aluminum plate heat bed with a 110vac 1200w Keenovo heating pad. The purpose being for quick heat up.

At 100% PWM the heat time is 2-1/2 minutes to 80c from ambient (20c) but I get an over-power warning. On the PID tuning I decreased the PWM percentage by 0.2 increments until I no longer got the warning at PWM of 20% but at the cost of a 16 minute heat time.

If I use the PID values at the level that did not trigger an over power warning do I need to use the lower PWM value in the M307 or can I run a higher PWM value with those PID settings?

Or do I run at the PID values of a higher PWM % that give a reasonable heat time and rely on a thermal cut-off fuse for protection?

Not sure how to interpret all this???

Basically it's telling you what temperature the bed might reach if there is a fault that causes the bed to run at full power. You have to assume that under fault conditions there could be 100% PWM. So when using fast bed heaters like yours, it's wise to mount an over-temperature cutout on the bed and connect it in series with the bed heater.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Is it correct to say that if the PID tuning (at whatever PWM% I chose) is stable, I use those PID values and rely on the thermal protection I am comfortable with in case of a fault, regardless of the warning?

Whether you add a thermal cutout is up to you; but if the predicted temperature at full power is significantly higher than the temperature limit of the heater, then I recommend it strongly. Thermal cutouts are commonly used in domestic appliances for similar reasons.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Can you recommend a thermal cutout for us plz

Yes I am running a thermal fuse.

something like this:

[www.aliexpress.com]

just held onto the bottom of the hot bed and wired in series I take it?

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JustSumGuy
something like this:

[www.aliexpress.com]

just held onto the bottom of the hot bed and wired in series I take it?

Yes, but pick a lower temperature one because 260C is too hot for a silicone heater.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

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dc42

Quote
JustSumGuy
something like this:

[www.aliexpress.com]

just held onto the bottom of the hot bed and wired in series I take it?

Yes, but pick a lower temperature one because 260C is too hot for a silicone heater.

I read 200c in that link...

I have a 24v MK3

I'm using a NTE8182 thermal fuse with a 192c cutoff. It was recommended by others to stay away from the no-name imports from China due to inconsistencies.

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jbolt
I'm using a NTE8182 thermal fuse with a 192c cutoff. It was recommended by others to stay away from the no-name imports from China due to inconsistencies.

I am sure its made in china regardless, I dont buy into that hype and after spending thousands on aliexpress over the last decade I haven't experienced it either.

That said, how did you mount it? just put it under the heat bed?

My bed is 1/4 aluminum so it is clamped to the back edge similar to the example in this thread, fourth post down. [forums.reprap.org]

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jbolt
My bed is 1/4 aluminum so it is clamped to the back edge similar to the example in this thread, fourth post down. [forums.reprap.org]

tqvm