SKR Mini E3 V1.2 wrong temperature measurement

[Magoo0876]

Hi,

I've played a bit with the new SKR mini E3 V1.2 board and liked it so far, but something was strange. After some time I've measured the head and bed temperatures, and they were too low. My sensors are 104GT-2 on the bed and B3950 on the hotted .

bed set to 60 measured 50 hottend set to 200 measured 160

I've played with the pull-up resistor setting and found that 6k almost compensates the error. Also different sensor type settings did not do the expected.

So I think the internal pulldown resistors of the STM32F102 are activated and this would cause a higher temperature reading for the software. I also tried to activate the pull-up resistors for the thermistor input pin, but this is not a possible setting in the config.

Thank's for your help.

klippy.log

[ArkadiuszRaj]

Clear and I agree with you.
Now a bit waiting till they publish schematics of new SKR mini E3 v2.0

[markwinger]

You are correct about the problem. However, for noise problems (there seem to be a lot) there should also be a cap or 2 from 3.3V_A to analog ground. They should either add to more caps 10uf and .1uf 3.3V_A to ground or simply move C18 and C19 from 3.3v to 3.3V_A since there appears to be plenty of capacitance on 3.3V already.

[markwinger]

Now I am seeing the bed temp read wrong. I am doing a print, bed temp reads 70C on the display but my ir-scanner says 61C. Running with DIV8 (current version on github) so I dont know whats going on now. I have LV1 and LV2 bypassed, and some ferrite chocks on supply wires.

[markwinger]

just for reference, I rebuilt with DIV4. No help/ I currently have to set bed temp to 77C to get 70C. Makes me wonder how far off the hotend temperature is. Cant read that with an IR scanner.

[markwinger]

I just realized I have aticks=4 as Kevin suggested earlier. I will try it back at 3 when the current print completes.

[markwinger]

I think the discrepancy is the glass bed I am using. It measures correct when I switch to my magnetic build surface.

[fabicodes]

@thebrakshow so you still suggest bridging the ferrites LV1 and LV2 for the best results?

[markwinger]

This is the best I've seen so far and I am currently running this way. This is a current temp graph and the bed temp measures correctly.

[KevinOConnor]

I'm going to close this issue as it looks like there is a solution for the original issue. (The board has a hardware problem, and the only complete fix is to make a hardware fix as described at https://github.com/KevinOConnor/klipper/issues/2194#issuecomment-625424122 ).

-Kevin

[positron96]

BTW, mini E3 v2 seems to have this issue as well.

https://github.com/bigtreetech/BIGTREETECH-SKR-mini-E3/blob/master/hardware/BTT%20SKR%20MINI%20E3%20V2.0/Hardware/BTT%20SKR%20MINI%20E3%20V2.0SCHpdf.PDF

[EatMoTacos]

BTW, mini E3 v2 seems to have this issue as well.

https://github.com/bigtreetech/BIGTREETECH-SKR-mini-E3/blob/master/hardware/BTT%20SKR%20MINI%20E3%20V2.0/Hardware/BTT%20SKR%20MINI%20E3%20V2.0SCHpdf.PDF

Do you how to fix this on the V2 board? Which pins need to be shorted out like the commend mentioned above?

[positron96]

BTW, mini E3 v2 seems to have this issue as well. https://github.com/bigtreetech/BIGTREETECH-SKR-mini-E3/blob/master/hardware/BTT%20SKR%20MINI%20E3%20V2.0/Hardware/BTT%20SKR%20MINI%20E3%20V2.0SCHpdf.PDF

Do you how to fix this on the V2 board? Which pins need to be shorted out like the commend mentioned above?

I went with purchasing MKS Robin E3, so I don't know, but probably the same pins as in V1.x.

[markwinger]

My E3 x-stepper driver failed, so I ordered an mini E3 v2. It came DOA. I had the same issue with my first mini E3. So in frustration I returned it and decided to try a different manufaturer. I bought a creality v4.2.7 (and saved 10 bucks). I updated printer.cfg and the new board worked first try.

There is no temperature issue with this board running the latest klipper firmware with no mods.

[michaelmargolis]

BTW, mini E3 v2 seems to have this issue as well.

The link in that post actually indicates that the V2 board does NOT have this issue, the chokes are not in the schematic for the V2.0 board. My V2 board purchased at the end of last year has consistently maintained temperatures within half a degree of the setpoint requiring nothing more than a PID autotune.

https://github.com/bigtreetech/BIGTREETECH-SKR-mini-E3/blob/master/hardware/BTT%20SKR%20MINI%20E3%20V2.0/Hardware/BTT%20SKR%20MINI%20E3%20V2.0SCHpdf.PDF

[positron96]

Hm, you are definitely right. I really don't know how I came to that conclusion after looking at that schematic...

[sakoula]

The hardware fix is nice, but there is still a bad behavior of the board. Heat the hotted and then switch the bed on and off. As you already see in the graphs above, the hotted temp drops when you switch the mosfets on. That destroyed the same print two times on the same spot because if you find a switching sequence the hotted temp will oscillate and reaches the max limit, klipper stops. I replaced the board with the cheetah 1.1b and i'm happy again.

Hi There,

I really apologise of replying on a closed issue. I have an skr mini v1.2 for some months now and recently I started using klipper. I noticed on the sample config of the board the lines

# Note: This board has a design flaw in its thermistor circuits that
# cause inaccurate temperatures (most noticeable at low temperatures).

and then I found this thread. Reading through the thread I am under the impression that #2194 (comment) hardware fix does not completely resolve the board issues. Is this true?

I am not planning on getting a different board at this point and I am wondering whether the hardware fix will solve the issues or will introduce some other problems.

sorry again for replying here, thanks for your help and @KevinOConnor thanks for this great piece of software!!!