Solved I'm having a bed heating problem, in that it is "stair stepping" instead of heating smoothly

[BeepDog]

Printer Model

V2.4

Extruder Type

Orbiter

Cooling Type

Stealthburner

I have posted in the discord too, and I'll update this thread with whatever I learn there, so that this stays around, because I couldn't google things to get this figured out.

Why would my heated bed be heating in "stair steps"? I have double and triple checked my bed thermistor connections. They're definitely attached, and I'm reasonably confident the bed temperature is reading accurately. Though I don't own an IR camera or IR thermometer to check. When I told it to get to 60C, it did that, and it definitely wasn't too hot. Going to 105, however, is not succeeding at all.

Bed is limited to 60% power cycling rate. This was all working fine up until recently, where I replaced some of the panels, so I had taken everything apart. I put it all back together, and everything is connected with MicroFits or Heavy Duty AC connections, so I'm confident it's all connected well.

I haven't yet tried another thermistor connection on the octopus, to see if that's the problem. I haven't changed any configuration recently, and it was able to get up to 105 smoothly in the past. And the Revo hotend very smoothly heats.

• Is it going bad, and I need to replace my bed heater?
• If I need to replace my bed heater, how do I go about doing that?
• Can I peel off the old one and slap on a new one, or should I just go ahead and buy a whole new bed?
• Is it possible to replace the thermistor?
• Is it my SSR failing?

 

[BeepDog]

A suggestion was made to clear all the browser caches and reload the page. I have done this, but I don't think it has cleaned up the heating rate.

Tried that again, and started the heating, and we got all weird, and actually LOST temperature at this point and then klipper panicked with not heating at expected rate (as it should).

 

[BeepDog]

A successful PID tune of the bed when I set the power to 1.0. I never had this odd stair step in the past, but I can use a higher power level anyway, as that'll make everything warmer faster, and will help with the bedfans heating the chamber.



I was informed on Discord that the old math that would limit your bed to 60% power max, isn't actually valid any more, and won't warp the beds that most people use. I have a quality Omron SSR, so that will handle the current as well, and it didn't overload my house circuits.

I'm able to heat the bed successfully at this point, so the answer was USE MORE POWER.

If anyone knows the new math logic behind what one should limit their bed power levels to, I'd like to know. I've got a 750W heater on a 350mm bed that's 8mm thick.

Regardless, at this point I'm going to mark this solved!

 

[Sandman50]

IIRC, the power limit is to reduce the thermal gradient through the bed as it heats up. The theory is that the heater pad is heating up faster than the AL plate can absorb it causing thermally induced stresses leading to the dreaded "bed taco".

 

[BeepDog]

IIRC, the power limit is to reduce the thermal gradient through the bed as it heats up. The theory is that the heater pad is heating up faster than the AL plate can absorb it causing thermally induced stresses leading to the dreaded "bed taco".

Right! That's what I thought too, and yet when I asked on the voron discord, I was informed by well-known members that that math is "old Math"

it's in the voc_gchat, so you gotta have a voron, but I was told that the limitation is from "old, incorrect math"

From @Sanity Agathion:

You'd need like 50 kW to permanently taco bed that we use
Bed will be totally fine, I asked for SSR because if you are in 120V land, you may overload it [the SSR]

 

[Sandman50]

The other side is that even at ~60-65% it still only take a couple minutes to warm up. For me, heating the chamber up, even with bed fans, takes far more time. So a very minor addition in a ~30-40 minute process isn't a big deal. So 0.65 is where I started and where it will stay.

 

[NoGuru]

I have been running the bed at 100% for over a year, no issues, bed still looks great. I see no reason to slow down the heat up process.