Need a favor from a MK2 owner  

Re: Need a favor from a MK2 owner

Hi Steve,

thermistors are low cost, simple temperature controlled resistors, they are not very accurate...

they are however generally reasonably consistent and generally reliable if treated with care... which is why they have been adopted for 3D printers

typically if you have an open circuit thermistor, the rambo will still show a low temperature, again, this is not a precision device and as you approach infinity, it's inaccuracy becomes most apparent.

my rambo drops to around 11centigrade when the thermistor cable breaks most rambo's end up below 15 sentigrade, which is why Prusa have hard coded a minimum error temperature of 15 centigrade or there abouts...

it looks like your rambo has a slightly higher minimum temperature... is your environment humid?

mintemp is intended to reduce the possibility of undetected high temperatures when heating a device with a defective thermistor.

some of us find this an issue in cold weather, so you will hear stories of folk using hair driers to warm the printer above mintemp, so that the rambo will allow the heating process to begin...

you will almost certainly find that the two printers prefer different temperatures for the same filaments...

just accept it, it's unlikely that you can easily engineer both printers to agree at all points on the temperature scale.

hope this helps,
regards Joan

Re: Need a favor from a MK2 owner

I am trying to figure out why my MK2s MMU bed and nozzle temps read about 9c above room temp.
I have plugged in another thermistor and it is the same.
The room is about 20c.

What I find strange is that when I unplug the thermistors from the board, the temp display drops from 29c to 20c. I would think that it should drop to 0c or error.

When I unplug the thermistor from the board of the MK3, it drops to 0c.
I did not even realize the issue until I got the MK3 and noticed the initial room temp readings did not agree.

I flashed the firmware to the latest MMU, to just the MK2s, and even to one from the middle of last year and no change in temps.
My next thought is the board itself, but it is not something I just want to guess at.

Would someone be willing to unplug one of their thermistors and tell me what the display changed to?

Thanks, any insight is appreciated.

You made me curious so I did what you asked.

In my case:

MK2sMMU all stock
Firmware 3.1.0
Measured Room temperature = 25.5c, Humidity = 48% (We just had a cold front come through 🙂
Heatbed LCD shows = 26c, Measured = 25.9c
Nozzle LCD shows = 26c, Measured = 26.4c

The measurements were taken with a Fluke IR Thermometer.
I have an MK3 sitting right next to the MK2sMMU and it shows 25c at rest so they are both within my idea of tolerances.

Then I unplugged the heatbed thermistor as you asked and the temperature dropped immediately to 9c and I get Err: MINTEMP. It then 'floated' between 8c-9c.

I know it does not solve your situation but at least it lets you know mine does.

Jerry.

Re: Need a favor from a MK2 owner

Thanks. That is just what I was looking for. Strange that you got a MINTEMP error and I don't. I just unplugged both again and they dropped from 25 to 19c. Left the bed unplugged and ran self test and it error'ed after the bed got up to 39c (IR camera).

Still not sure why the board is not detecting the thermistors being unplugged.

Thanks again for the feedback.

Re: Need a favor from a MK2 owner

Thanks. That is just what I was looking for. Strange that you got a MINTEMP error and I don't.

A thread in another section metions that the MINTEMP error turns on when the temp falls below 16c. You were at 19c and I was at 9c. Works as designed 😉

Re: Need a favor from a MK2 owner

I wonder where the temp is being picked up if both sensors are unplugged. If it is a set number, they should all be the same I would think.
Thanks.

Re: Need a favor from a MK2 owner

There must be a reference temp sensor or something on the board itself. I just unplugged both sensors and warmed the board up with a hair dryer. Turned the printer on and both read 28c. Room temp is 20c.

Then I turned the heat off and blew cool air onto the board and got them to drop to 24c.

Crazy.

Re: Need a favor from a MK2 owner

The thermistor is attached to an analogue port. As part of a voltage divider. I believe there is a reference table in firmware to compare rhe results against. I am not aware of a gcode option or similar, to revise the temperature range

I expect you would need to test several temperatures on YOUR printer and revise the appropriate table. Then recompile the firmware as a custom firmware for your printer. And you might get it to perform bette. Unntil the next firmware upgrade. At which time it is likely that you would have to create another custom firmware to revise the table. Forever...

It is unlikely to ever match any other device exactly.

Most folk i know simply accept that their printer shows a bit high at rest.

If you find that it likes different indicated temperatures. Make a note and accept the diference..

For instance. People are all different and we generallyy accept that... (i bet someone else will have diferent advice for you here. 🙂 )

My mk2 likes about 190 for pla. My mk3 likes hotter...

Joan