My build with the Hypercube Evolution continues with a replacement BIQI KFB2.0 board. I am not at the printing stage yet. This is due to my latest problem.

The kit contains a “no-name” hotend, complete with round finned heatsink and nozzle. Looks a bit like a V5 J Head Hot End.

Everything is wired up. A 24 V power supply is being used. The printer is connected to Pronterface via USB. Using Pronterface, I set the hotend temperature to 70 °C. The KFB2.0 board lights a bright red LED when power is being sent to the hotend (and/or the heated bed). On initial heating, the red LED is on until the hotend temperature reaches around 65 °C and then turns off. The temperature continues to climb to around 120 to 125 °C, then starts falling. At 69/70 °C the red LED comes on again for about two seconds, the temperature continues to climb after the red LED is off to around 86 °C. It then cycles around the 69/70 to 86 °C position.

I have removed the thermistor to check its resistance. Reads greater than 100 kΩ. When in situ in the hotend, it was reading around 85 k&ohm, but a bit of Kapton tape sorted that. I was now reading 100 k&ohm with the thermistor in place. I then used Pronterface to set the temperature again. This time with a multimeter hooked up to the hotend terminals on the board. It confirmed that the bright red LED was sending 24 V and nothing when not on, so the hotend is recording a temperature increase from around 65 to 125 °C with no power. But, I now got something different when the temperature fell back to 69/70 °C. The red LED flickered for about two seconds and the multimeter showed readings fluctuating between 0.1 and 4.2 V. From this point the hotend kept the correct temperature, even after I had removed the multimeter.

Has anybody any idea why the temperature is going so high and what can I do to fix it?

  • $\begingroup$ What is the resistance of your heater? $\endgroup$ – Perry Webb Nov 2 '20 at 17:03
  • $\begingroup$ @PerryWebb 3.9 ohm $\endgroup$ – Ramblin' Sid Rumpo Nov 3 '20 at 3:45
  • $\begingroup$ Basically the resistance of the heater element is too low causing large currents and fast heating of the hotend. The overshooting you describe is the result caused by the active PID schedule. However, PID tuning is not always possible when you use wrong heater cartridges. I've made this a duplicate of an existing question. $\endgroup$ – 0scar Nov 3 '20 at 15:33

3.9 ohms is a 12V heater. It won't work on 24V.

  • $\begingroup$ Thank you. You would think that the suppliers of the kit would include the correct parts. I will try a DC-DC converter to drop the voltage. $\endgroup$ – Ramblin' Sid Rumpo Nov 4 '20 at 6:03
  • $\begingroup$ Heaters cost lest than a converter. $\endgroup$ – Perry Webb Nov 4 '20 at 9:35

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