3D Printing: Adjusting Bed Temp values on Monoprice/Wanhao I3 (Repetier Firmware)
Channel: Roel Van de Paar
Date: 2019-06-29

3D Printing: Adjusting Bed Temp values on Monoprice/Wanhao I3 (Repetier Firmware)


The Question: I have a Monoprice Maker Select, which is a rebranded Wanhao Duplicator I3 V2
(Prusa clone). I've found that the heated bed temperature values on the LCD are
incorrect. The heater works, and the controller maintains the bed temp just
fine, but the temperature reported isn't the true temperature. When using the
PLA preset, with the bed set for 60?C, once the temperature stabilizes at 60?C
on the display, I can measure it with a laser thermometer and get a consistent
54?C across the buildplate. With the ABS preset of 90?C, I read 80?C. And with
the bed set for the maximum value of 120?C, I'm only reading 102-104?C.
I've checked these values with the bare aluminum build plate, and I've allowed
the temps to stabilize for at least 10 minutes to ensure that I have consistent
readings. I believe the the firmware is using the wrong temperature curve for
the thermistor in my device.
I had hoped that there was a simple scaling constant that I could adjust, but
that doesn't seem to be the case. I've researched enough to learn that my
device is running Repetier 0.91 firmware, and github.com/repetier/
Repetier-Firmware/wiki/Temperature-control on the Repetier wiki says that each
type of thermistor needs a custom voltage-＞temp lookup table, and talks about
building a custom table in "configuration.h". I've tried to follow this line of
research but I feel like I'm going around in circles. It sounds like I could
build a custom version of the firmware to install on my printer, and in doing
so I could potentially specify a better conversion table. This gives me pause
for several reasons:
 1. I haven't found any online reference to other people installing a custom
 Repetier build on a Wanhao I3.
 2. I have no idea what values to use for the temp conversion table.
 3. I can't even find anyone else reporting my issue.
 4. I'm fairly new to this; I rather not brick my printer, and I haven't
 found any good guides to installing firmware on the device either.
 5. I'm not convinced this is the right option. Should I be looking at
 replacing the thermistor instead? And if so, what's the correct part?
I've also looked into the Melzi board inside the printer hoping for a variable
resistor to tweak the thermistor voltage divider, but no such luck, at least in
the schematics.
I could just live with it; I've been using a 67?C setting to achieve a true
60?C bed temp for PLA, but I'm starting to work with ABS and I'd like the
option to get above 100?C bed temp. Am I on the right track? Suggestions? I'm
still pretty new to the device and 3D printing in general, so I may have
overlooked something obvious.
Update: additional question in light of Tom's answer: what is the expected max
actual bed temp achievable on a Wanhao/Monoprice I3? I'm measuring 100?C with
an LCD reading of 120?C, but I'd like to get to 110?C if possible.

Solutions: Please watch the whole video to see all solutions, in order of how many people found them helpful

With thanks & praise to God, and with thanks to the many people who have made this project possible! | Content (except music & images) licensed under cc by-sa 3.0 | Music: www.bensound.com/royalty-free-music | Images: stocksnap.io/license & others | With thanks to user Tom van der Zanden (askubuntu.com/users/26), user Jason Clark (askubuntu.com/users/2541), and the Stack Exchange Network (3dprinting.stackexchange.com/questions/1520). Trademarks are property of their respective owners. Disclaimer: All information is provided "AS IS" without warranty of any kind. You are responsible for your own actions. Please contact me if anything is amiss at Roel D.OT VandePaar A.T gmail.com.