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Thermistors decouple

Taxus812Taxus812
edited August 2016 in Questions & Answers
Ok I dont know what to do at this point.   I have replaced the Adruino Mega, the RAMP1.4 board and the PSU to a very clean one for ham radios (very low ripple 12v). 

If I heat both extruders they decouple and the temps drop.  in frustration I set the EXT0 and EXT1  DECOUPLE_TEST_PERIOD to 300000 and actually watched the temps rise get up to around 100 C and then just start falling.  So they indeed decoupled. 

If I heat each extruder individually it heats and holds its temperature (same with the bed).  So the Thermistors are working 

I watched the current output on the power supply and it is below 16 amps (total 5amp circuit and 11amp circuit).  Typically bouncing between 3 and 10amps. If I heat just the two extruders the current draw is 7 amps

I have spent countless hours working through all the settings.  I have everything mechanical worked out. I just cant get past this one and dont know where to look. 


Help Please. 

Comments

  • Taxus812Taxus812
    edited August 2016
    Additional note:
    If I heat Extruder 1 to 215 C. Then heat Extruder 2, both thermistors decouple when Extruder 2 reaches about 170-190 C. 

    The stepper then start making weird whining noises.  Emergency stop resets and I can start heating immediately if desired. 

     
  • Taxus812Taxus812
    One last hardware thing to check and that is the wiring to the heater and thermistor.  Hope that solves it. 


  • RepetierRepetier
    You can disable decouling test by setting the test period to 0.

    But as I read your posts you seem to have a problem when power consumption gets too high. So maybe you install repetier-server so you can watch bed and all extruders at once and see how they influence each other (decoupling disabled for testing). Often voltage drops if too much current is required and that means less watts to heaters allowing them to cool down. But seems like a wicket problem.
  • Taxus812Taxus812
    edited August 2016
    You are right. I appreciate the validation that the issue is voltage and not incorrect settings. 

    I stayed awake all night and checked all the wiring.  Individually I didn't find anything.  What I did find is, the heat-resistant tubing on one of the ceramic heaters wires, had slipped back exposing the wire. I could not tell for sure but I think it was hitting the side of the case (or the other lead).  I pulled the heaters and repacked them so the heat-resistant tubing would not slip and put the head back together. 

    They seem to work perfectly now.   I certainly have a MUCH better appreciation for the decoupling feature in the firmware.  It really works and work well. 

    Terry

  • Taxus812Taxus812
    edited August 2016
    Well its back.   However I have a better description of what is happening for others who are reading. 

    I noticed the fan shut off about part way through the heating cycle . I assumed it was the software shutting it down while it heats the extruder.  so I put a volt meter on the D9 and D10 pins for the extruder heaters and observed a heating cycle . 

    What is occurring is sometimes during the heating cycle, power is disconnected from the D9, D10 and FAN . The heating light goes out on the board for D9 and D10.  In Repetier it still shows power being applied.  The thermistors lag behind the heaters a bit so Repetier does not see the heaters have "decoupled" (I say heater only because the thermistors are actually working)

    D8 (heater) continues to function and maintain heat.  

    Now I figured it out for sure.  

    if I have two 40w heaters firing up at the same time, that is a total 80w @ 12v drawing 6.66 Amps on a 5 Amp circuit.   So it seems my extruder heaters are simply overloading and shutting down the 5a circuit causing all my grief (which explains why the steppers are whacking out). The adruino is then being powered by the USB. 

    Now I have to figure out how to limit the current by staggering in the heat-up cycles so they are not both not fully powered at the same time.  (or limit the total power to 75%)



  • RepetierRepetier
    They will always turn on at the same time, but maybe the fuse has some lattency so if not all are at 100% the fuse will not trigger. Reduce max pwm for your heater and hope you can still reach target temperature. For PLA it should be no problem.
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