Extruder heater not providing enough heat

I just modified my delta printer to include a fan to cool the Arduino/RAMPS boards. In the process I took the board fan wires, the extruder fan wires and the proximity sensor power wires and attached them to the third set of terminals on my power supply. The extruder fan and the sensor were formally connected to the 12V input terminals on the RAMPS board, but those terminals were becoming overcrowded. The problem I have now is that the extruder fails to heat up to the target temperature (200C). It gets to about 120C and then I get a 'heater decoupled' message. Increasing the decoupling test period to 30 secs results in a slightly higher temperature before the heater decouples. Disabling the decoupling test gets the temperature up to about 160C, but then it flat lines and won't go much higher. Before I added the board fan and changed the power connections the extruder would heat up to the target temperature quickly and steadily.
Is my problem related to changing the power connections (i.e. is the RAMPS not getting sufficient power) or is there some other problem here?
My PSU is 12V/30A with 3 output terminal pairs:
1. RAMPS/Extruder
2. Heated bed (which heats up properly.)
3. Extruder fan, electronics fan and proximity sensor

The Repetier-Host log shows the following when the heater decouples:
11:10:07.773 : DebugLevel:14
11:10:07.777 : Error:One heater seems decoupled from thermistor - disabling all for safety!
11:10:07.778 : Error:Temp. raised to slow. Rise = 0.99 after 13080 ms
11:10:07.780 : Disabling all heaters due to detected sensor defect.
11:10:07.780 : DebugLevel:14

Does anyone have any useful suggestions?


  • Check your max pwm settings. Often it is not set to 255 so it will limit maximum power possible. You also see this in host/server temperature graph that the power doe snot go to 100% in this case.

    If it goes to 100% and you can not go higher then the limit of the heater is reached. Can happen if you cool the extruder too much especially the hot end should not be cooled at all. You cool the filament coming out and above the heater zone to not allow heat rising to top. Sometimes hard to control what gets cooled.
  • I checked the extruder power curve and it was going to 100%, but the extruder temperature curve was flattening out at the 120C point. I checked the temp. curve on my Cartesian printer and it is a steady upward gradient right up to the target temp.

    So, I took the extruder apart, cleaned it and reassembled it (there was some play between the hotend and the rest of the extruder before.) Now everything works fine - it heats up to the target temp. within about a minute in a steady straight gradient.

    Thanks for your tips.
  • Are the 3rd set of terminals on the power supply physically the same as the other terminal, some power supplies have a seperate lower amperage output.
    Measure the voltage coming out of the power supply to make sure it is stable at 12volt when under load.

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