Wrong temperature when using heated bed + glass pane

K8200 3D Printer K8200 - Wiring and electronics
1

Hi guys,

I’ve been having some great fun with the K8200 lately. However, for some reason I don’t seem to measure the correct temperature for the heated bed. I would like to hear your opinion on the following:

I have the standard heated bed with a 100k thermistor soldered on the bottom. When I turn on the heated bed, I am measuring realistic values and the bed reaches temperature fairly quickly. I confirmed my measurements by placing another thermistor on top of the bed, and attached it to the hot end thermistor pins for readout. Everything OK so far.

However, when I start my heated bed while I have a glass pane (3mm thick) on top, I am not able to reach temperatures of 45C or higher. However, the glass pane is incredibly hot, to hot to put my finger on for more than a second.

Is there a common explanation for this problem? Does anyone know a solution?

Thank you in advance, N3lis

2

What do you mean by can’t reach?
Does the printer report 45°C max or does the heatbed really stick at 45°c?

Have you checked with a thermometer?

3

So… for some reason the problem magically disappeared and I cannot reproduce it… Murphy’s Law I guess :wink:

Thanks for your help anyways :slight_smile:

4

So, the problem is back and I managed to do some measurements:

I have measured the temperature in the center to be the same temperature as my heated bed NTC was measuring: about 45 degrees Celcius. However, the temperature at the sides of the board quickly increases to 80+ degrees Celcius… that’s when I turned the bed off to save my bed.

Now, it turns out that the problem was gone because I used insulated clamps to hold my bed + glass pane. However, when I put screws through the holes, the problem starts. I found that the screws make an electrical connection between the frame holding the bed and the power supply, burning up a decent amount of my power…

5

Hy,
you should check the wires from the bed to the main board, maybe you have a short circuit ?
I had same problem, then I change original 4 mixed cable by a silicon 0.75 mm cable, the heat bed reach much more rapidly high temperature than the original conection.

6

Thanks :slight_smile: might do this as well. Found some tiny scratches on the bottom of the heated bed, making a connection with the frame and thus shorting the circuit :slight_smile: