Heat Block Cables Show Out-of-Range Resistance

Discussion in 'Calibration, Help, and Troubleshooting' started by DataJunkie, May 9, 2020.

  1. DataJunkie

    DataJunkie New Member

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    I've had to dismantle two shared Prusa MK3 printers due to bad clogs, one of which was caused by a bent (??) heat break and I had to melt out the clog. Both of these use an E3D v6 though apparently there is a minor difference between the Prusa version and the retail version.

    I fixed the clogs, but before putting everything back together, I tested the red heat block cables with a multimeter and got a high reading of 16 ohms, where 15.1 is supposed to be the highest. The other printer was even higher at 19 ohms. Since I used a torch to melt out the clog, I was worried about the cables being damaged though I don't see any damage.

    Are these readings problematic? What issues might I face if I continue to use the machines? Should I replace both heat blocks?
     
  2. Old_Tafr

    Old_Tafr Well-Known Member

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    First, do you have the original resistance measurements from the heater (cartridges? not "blocks" ?) If you don't have these then you don't know if or how much they have changed.

    Though difficult to remove this would seem preferable than using a torch to free a clog.

    Several electrical checks to make.

    A. Continuity
    B. Resistance
    C. Insulation resistance

    "A" You have done and assumed that moving the cables around especially where they meet the cartridge there is no loss of continuity.

    "B" You have done (take care with all connections especially if using croc clips as these could affect the reading by one ohm at least.

    "C" = High resistance between either lead and body, I have never measured this, will if I can find a cartridge not in use. I would expect to be the the megga ohm range. If low then post what it is and I will check mine.

    Next, does the difference in reading make any difference, so do the sums for watts = I squared R or V squared over R. If 12v ?? (or are they 24 v ? ) then 144/16 = 9 watts, and 144/19 = 7.6 watts

    Seems like they are 24v? 576/16 = 36 watts 576/19 = 30 watts

    You could try simply heating and using Octoprint or whatever see what temp you can achieve?

    Do you have an unused heater you can check resistance of ?

    Best plan is remove the cartridge before heating with a torch.
     

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