After looking at prints between different printers of mine using Duet Wifi boards, investigated hot end temparatures and using a Fluke IR heat gun… the external temparature of the brass nozzzle is 175degC when snapmaker thinks its 200. Also takes 270deg commanded to get 230 and yes my thermisor is secure. Thats quite a margin for error, yes I can offset in CURA as I dont use LUBAN… but all my materials are setup and configured correctly for all my other printers whos hot ends are calibrated
Some Snapmaker, can you open up the M305 command in the Marlin Firmware for us… much easier than me redoing it off GITHUB!
Infact the M303 auto PID heater tune command is in enabled in the firware but doesnt work… that would be useful too!
Ok… did a little digging in the Git Hub Marlin Source… Configuration.h defines hot end as Thermistor type 1
This is a 100k thermistor and the temp table says at about 98.5kOhms. well i tested mine with a multimeter and its 125kOhms at room temp. So that will be why…
Im gonna replace my thermistors with better ones…
Can anybody confirm this?
Sounds interesting!
For info, this is the thermistor temp table… resistance left column (985 being 98.5KOhm) and the temp in deg C on the right. Ive bought a differnt brand of 100kohm thermistor with a different betacal just to try… as thats quicker for me at moment than recompiling the firmware
They may have intentionally done as such to hide the fact their hotend can’t get up to as high as they claim.
Wouldn’t put it past em.
The firmware code you are looking at is for Marlin’s support for interpreting the sensor values but that isn’t used on the Snapmaker for the Noozle thermistor. The thermistor is read in the module itself and the controller receives a preprocessed value in °C.
The actual thermistor table is in the module firmware repository. The table there is not so easy to read since it doesn’t directly contain resistance values, but if the chinese formula at the top comment is correct, the table pretty exactly mirrors the Rnor column of the table mentioned in the comment. If I understand that table correctly, 125kOhm should correspond to 20°C.
@zauguin Thanks for the reply and clarification. Interesting Ill check the snapmaker thermistor value in boiling water (I’m at sea level so pretty much 100deg C) see how it checks out. At which point if all good then the somewhere in the chain A/D, table values or the maths the calculations for C ends up being lower than it should be!
Worth someone else testing with either a thermal camera or better yet a known, calibrated thermistor that you can screw into the heat block just to double check
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I ended up getting a custom firmware compiled by a guy on here with altered lookup table.
Would be interesting to see if anyone else has inaccurate temparature readings on their print head, or whether mine just faulty somehow