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Solved Thermal Runaway on Bed heater

Discussion in 'Troubleshooting' started by Doug Meek, Apr 9, 2017.

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  1. Doug Meek

    Doug Meek Member

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    Just yesterday my printer started giving me this error every time I attempt a print. It will go for awhile (5-10 layers) and then pop up ending the print. I just monitored it and it looks like the commanded temp of 55 is dropping to 51.4 or so and then giving the error. Are there any common things to look at?

    I replaced the flat cable clamp with the one from Thingiverse and covered my bed heater with aluminum tape to eliminate it catching on the crap under the bed when it sagged several months ago. Nothing has changed recently.

    I also have replaced the tiny little fan under the RAMPS board with a 120 mm thin fan so it shouldn't be a cooling issue.

    The printer is only about 6-7 months old. Right now I am heating the bed to 55 and watching to see if it does it just sitting still.

    Any help would be appreciated.

    Also I was thinking about enabling PID for the bed but the instructions I found say to enable PIDTEMPBED and BED_LIMIT_SWITCHING but when I try to compile I get an error about not being able to enable both of those. In reading further I'm not even sure I should enable bed PID with the stock heater, should I?
     
  2. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    PID temp on the bed is not a huge help, but you could disable the bed runaway temperature warning.
    Comment out: THERMAL_PROTECTION_BED like this

    #define THERMAL_PROTECTION_HOTENDS // Enable thermal protection for all extruders
    //#define THERMAL_PROTECTION_BED // Enable thermal protection for the heated bed

    In configuration.h and recompile and reload.
     
  3. Doug Meek

    Doug Meek Member

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    Thanks for the temporary fix...I did disable the warnings and that allowed the prints to finish and monitoring the bed temps during the prints I saw it drop a maximum of 4 degrees from 55 down to 51 but that was the lowest. Is there a way to modify the code to allow more room without disabling it completely? I'd feel safer that way until I get the heater replaced and going to an SSR.

    Also what is the recommendation for replacing the heater and going to an SSR? Are 12V better than 120V, if I go 12V add another power supply or use the existing one? Silicone heater or other?
     
  4. Doug Meek

    Doug Meek Member

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    Well I found the problem, the connector for the bed heater to the RAMPS where the set screws hold the wires were slightly loose so when it started to draw current there was a small gap which caused arcing (minimal) and carbon buildup till it started acting like a resistor and thus started drawing excessive current until it went into thermal shutdown. From now on I will regularly (bi-monthly) start checking those for tightness. I ordered new male and female connectors from DigiKey and in the mean time the wires are soldered to the RAMPS, working fine!
     
  5. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Excellent job!
     
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