Hey, it’s freezing here, like 0.6c at the height of the sun if it’s out (relevant later), and I had a faulty automation setup power cycle my snapmaker to death.
Checked all the things, had usb-serial rx but no tx, had power at correct levels, touchscreen and usb-serial got no response from sent messages. Replacement controller needed. Obtained. Fitted.
First attempt at printer testing, wired in everything (silly) and booted, showed up greens except heated bed goes green then orange.
I’d seen that before with freezing winters so proceeded to home the machine, then check if heating the nozzle worked, and then the bed.
It quickly got out of wack at bed heating and said machine not responding, so I turned it off, disconnected the heated bed and turned it back on.
The machine said -15celcius on the bed briefly then went to orange - disconnected bed. I thought okay, I’ll reconnect and see what happens again, could just be cold.
Reconnect and it appears then disappears again (can’t remember if I then tried heating it). I think okay I saw something about checking resistances for the bed, I’ll double check those before assuming the bed is okay.
The technical support manual (software downloads on website for A350) has a section mentioning the pins. So I checked the Distributors Service Manual v2.0, which says to measure the resistance of pins 1+4 and 2+3.
Pins 1<->4 are around 2.5Ohms as desired.
Pins 2-3 are nearer 300kOhm instead of the desired 110kOhm, but that is surely a thermistor, and it’s currently 0.2degrees celsius in the garage where the printer is. The printer showed -15c when I disconnected the heated bed and booted the machine (and then no-bed).
So my question to support was what is the exact thermistor used, and can you provide the datasheet, so I may better judge what resistance should be at different temperatures?
I also wondered if anyone in the community was printing in low temperatures who could measure their heated bed’s thermistor value at nearer 0c than the manual measures. Also if anyone has attempted to profile/identify/replace the thermistor for the heated bed.
Just a thought: Marlin has thresholds implemented that indicate a failure of a part, like: If a thermistor reports below X°C, consider it broken/invalid. Perhaps your print bed is so cold that the firmware decides: Cannot be, the thermistor must be broken. And switches to orange. I’d perhaps try this: Get yourself a cooking pot (flat bottom) with warm water, put it on the heated bed (the thermistor is in the center), wait 2-3 minutes until the heated bed warmed up somewhat, then switch on the machine and see if it suddenly accepts the heated bed again. If so, I’d assume that you hit a threshold, and then the next step would be to see if this can be altered via GCode, via modified firmware, or to just make it a habit to put that cooking pot on the bed at freezing temp’s before starting your work.
Funnily enough I had planned to use a hair dryer for ten minutes (left pointing under the bed), but had a friend round so wasn’t in the cold garage very long.
Today decided instead on a hot water bottle. After looking at digikey.com for a replacement thermistor with a suitable value resistance at standard room temperature (~110 KOhm) I found that a standard 100.8K@25c NTC Thermistor from TDK has a resistance of ~310k at 0celcius which is what I was experiencing, and causing an error in recognition by the controller. It is 0.2celcius here today, so I tried using a hot-water bottle to warm the bed, and after ten minutes it booted and said 24celcius, and then I was able to tell the bed heater to turn on (30c first then 60). No replacement needed, just doesn’t like cold weather.
I had similar problems with a Prusa Mini where if the bed’s starting temperature was under about 12° it would error out and shut down. I used a little space heater to get it back in the zone, but the hot water bottle is an even more direct solution…
Yeah, 0C is the lower limit of the machines operating temp range. You can find this info on the SM website. You need to move your machine indoors if you don’t want to have further problems (bed temp sensor error is not the only issue you may run into).
To the best of my knowledge only the laser toolhead has an operating temperature, and it’s listed well above zero (too high for winter and too low for height of summer in the UK).
I appreciate frozen stiff metal things would be bad, more motor current draw until melting or failure, but assuming not frozen then I don’t see the additional issues.
In my head the firmware (marlin) has limits (artificially set, not per environment) as does the touchscreen logic, but that’s just faulty programming.
Also I already have a hairdryer attached to a SonOff remote control mains plug, left over from an experiment, so it’s a small step to setup and then I can remotely get a pre-warm done (just less hair washing in winter)
The Operating Environment temp and humidity limits apply to 3D printing as well. Like I said, you can find the info on the Snapmaker website; it is also listed in the User Manual for the machine. It is a bad idea to operate the machine outside of that range for various reasons, including reduced reliability and longevity of the components, and increased safety hazards, not just sensor issues. Those limits get set for many reasons, if you operate outside of them, you are on your own; don’t expect warranty coverage at that point either.
