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Solved Runaway Heated Bed

Discussion in 'Troubleshooting' started by Erin-Ellen Winfree, Jan 17, 2019.

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  1. Erin-Ellen Winfree

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    Hey again guys,

    I got frustrated after replacing my RAMPS board/adding a mosfet for the bed heater and gave up for awhile. I wanted to make a post detailing what i did, but I have been having different issues since I did this. Everything eventually seemed to be working, but I started having bed leveling issues and finally threw up my hands and haven't touched the thing in awhile.

    I finally decided to try again today and seem to have the leveling basically sorted, but now the bed won't stop heating at the set temp. I did a little digging here and around the web, but I can't find any posts with my exact problem.

    You guys have been very helpful in the past, so I thought I'd see what you have to say on the subject. I've posted a picture of my final setup. The mosfet has power coming directly from the power supply to the inputs, the outputs go directly to the hotbed and the plug port on top goes into D8 on the RAMPS. I've probably got something wired wrong, but I thought I followed the instructions I found.

    Thanks again. IMG_20181110_025327 (1).jpg
     
  2. Geof

    Geof Volunteer Moderator
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    wont stop heating, as in it keeps climbing until it errors out with max temp? or a PID tuning issue where its XXX degrees off ?
     
  3. Erin-Ellen Winfree

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    Thanks for the quick reply.

    It at least appears to keep climbing until it errors out. I haven't read the temperature at the bed yet. It only happened the once so far and I'm about to leave for work. What is a PID tuning issue?
     
  4. Geof

    Geof Volunteer Moderator
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    PID Tuning :

    If it keeps climbing I wonder if you have a bad SSR? (stuck on)

    Lots of options, a few better pictures of your wiring and board would help and some more detailed information since we cant see it would be helpful as well please.
     
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  5. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    PID tuning is a way of tuning how the arduino delivers the current (hot hot it gets and how quickly) so that it stabilizes faster.
    If yours never stops it is probably not a PID tune needed (but you can give it a try--my gut says it will fail).

    More likely a bad MOSFET on the bed heater channel. One that switches on and then will not switch off (unless the bed starts heating as soon as it gets power in which case it is just solidly failed ON). So the sad news there is that you need to try another RAMPS. You can try replacing the MOSFET, but it may not be the switch itself, but rather the circuit driving it. Your call (given how much generic RAMPS 1.4 boards are I don't spend a long time working on one).
     
  6. Geof

    Geof Volunteer Moderator
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    Hadn't occured to me but that is most likely the issue lol. I had assumed it worked fine prior to the SSR and after the SSR it did not...reading is hard lol.
     
  7. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Actually that is a good point, make sure that the input to the SSR is GONE (no volts) once the bed gets to temp. Maybe the SSR is stuck? That would be an easier fix :)
     
    #7 mark tomlinson, Jan 17, 2019
    Last edited: Jan 17, 2019
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  8. Erin-Ellen Winfree

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    Sorry for being unresponsive guys. I've been super swamped lately. What is the SSR? I googled it and got Solid State Relay, but I don't know where that is.
     
  9. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    @Erin-Ellen Winfree They are talking about the MOSFET, which is used as a solid state relay.
     
  10. Erin-Ellen Winfree

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    I suspected as much, but I didn't want to guess.
     
  11. Erin-Ellen Winfree

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    So I'm finally back at it. I've been through a few surgeries recently and haven't been messing with this printer much in the downtime.

    I finally decided to take another crack at it and just pulled the MOSFET entirely and connected the wiring back up normally. I'm still getting runaway temps on the bed though. The thermistor is reporting the temp correctly in Octoprint, it just doesn't stop at the set temp. I also noticed that when the print finishes and Octoprint reports that the bed and hot end are off the bed stays hot until I physically turn the printer off.

    Is this not some sort of software thing? I'm determined to get this thing back to normal this time, any help is appreciated.
     
  12. Erin-Ellen Winfree

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    Sorry to double post.

    I just read back through the thread and sure enough, as soon as I power the printer on the bed starts to heat up. SOOO, I guess that means that it's the RAMPS board? Did I maybe flash the firmware wrong to cause this? Or is this just a crap shoot when it comes to getting a good/bad board? I know they're cheap, but I seem to just keep needing more of them.
     
  13. Erin-Ellen Winfree

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    Ha ha, PID tuning fixed it. Pay no attention to me, I'm a big dummy.
     
  14. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    That is odd, because the output for the bed should not be enabled just on power on -- the slicer/lcd has to turn that one with GCode.
    Still, glad you got it sorted.
     
  15. Erin-Ellen Winfree

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    I imagine I did something stupid when I installed the firmware. Just turned it on again and I am not getting immediate heat on the bed. Thanks for all the help. I'm sure I'll break it again soon. ;)
     
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