My Bed temperature fluctuates(UPDATED)

[usajet]

My Bed temperature fluctuates between -290 to 1895 degrees C when the x and y stepper motors home. Any ideas what it may be? All the other programs don't react like that. I looked for loose connections and they are all tight. The printer doesn't shut down. But while printing it halts for the bed temp being ether to high or to low. My printer is a custom core xy using MKS Gen v1.4 board I PID tuned both hotend and bed.

I have used two different new thermistors and when I pull out the cable it goes to -14.

The spikes happen only when it hits the x and y endstops. Plus during printing.

[zemlin]

I'd guess you have a broken conductor in your wire harness.

[usajet]

Nothing it broken.

[wirlybird]

Your first clue is that the temps it is reporting are not possible.

Do you get these huge fluctuations on the printer display?

[dkightley]

A second clue is to consider how S3D displays the temperature graph:

It sends a message requesting the temperature at a specific interval and then waits. A response is read....and the response is displayed on the scrolling graph.

So...from the screen print, I can see that the requests are being sent. As there are traced points, I have to assume the printer is responding....and S3D is receiving the responses.


My conclusion is that either temperature values in the received messages are randomly wrong....or that S3D is randomly changing the value of the received messages. To me its highly unlikely (or even not possible) for the latter to be true....so it must be the former.

I think further diagnostics are needed.....such as a screen print of BOTH the communications log and the temperature graph.

[crisp90]

These are some of the useful tips given above. Heating and Cooling Toronto Looking forward to that.

[greybeard]

This may not be of much help but, worth the one-minute read…

Five yrs ago I had very similar problems and did quite a bit of work to understand the cause/solution… That was on a DaVinci printer I hacked.

I no longer have that printer and tossed out the stack of paper/notes so I recommend Googling a bit if problems continue after replacing with the correct thermistor and resetting PID to default. Check RepRap website (and Marlin…)

Here’s what I remember…

I tweaked the controller code, thermistor tables, manually set the PID, auto-tuned the PID… I jimmied up a resistor test network… I even added my own design for the thermistor circuit.

If you haven’t yet discovered, the code (for controller) may have look-up tables that are specific to various thermistors thus, if replacing a thermistor, you must use the same one (or tweak the code to use the correct one).

Two of the new (correct) thermistors I tried turned out to be bad. After testing a group of them with homemade circuit and heat gun (and ice-cube), I needed to reset the controller to use the default PID values - custom tuning and Auto-tuning caused nothing but headaches for the temp’s stability such that fluctuations of ‘one’ degree outside the envelope stopped the printer from printing. (There are code settings for ‘how much time to wait’ which can also be commanded via the cmd line input in Simplify)

During discovery, I disabled (in the code) the waiting for temp stability - that did the trick (temporarily). Finally, I had time to re-do all the settings and PID with a new thermistor and all was good.

I built two new printers from kits and after one year, the same problem happened - this time I knew enough to use the correct thermistor (and, again, found the first new one was bad!!! )…

Sorry I can’t be more help but, I recommend resetting the PID to default, disconnect the existing thermistor and use some jumper wires to a new thermistor and heat it (with hair drier, soldering iron…) to test it before installing on the bed…

[usajet]

Your first clue is that the temps it is reporting are not possible.

Do you get these huge fluctuations on the printer display?

They are not visible on the LCD Screen, Any other program. Only in Simplify3D.

[wirlybird]

Since I assume it is connected via USB I might look at that.

Make sure it is a good quality cable no more than 3 meters in length.
Use a USB2 port.
Make sure no cable extension, hubs or any other things like that.

Are you able to print via the USB connection?

Maybe there is a driver update.

Just thinking out loud!

[greybeard]

I didn’t mention that the two printers I built are MKS V1.3 (with RepRap Marlin).

You may already know to get the G and M code list where you’ll see code cmd’s to load defaults, set eprom, print memory… etc

The only notes I could find remind me to NOT use Simplify for entering commands but to use the Arduino IDE (notes are underscored in red ink). In the Arduino IDE, open the Serial Monitor, from there (top area) a command line input will do it correctly (don’t have Simplify connected during this).

Un-related to the above but, related to thermistor in code, below is screenshot for my MKS V1.3 (prussa I3).
There is also a section for the Printer Bed (just screenshot for hotend but, they are similar). You can see (glean) the importance to have the correct thermistor as the various codes/values are of importance.