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Bed not getting hot enough.

Discussion in 'Troubleshooting' started by tonycstech, Aug 2, 2014.

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  1. tonycstech

    tonycstech Active Member

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    Need it to get up to 110 or higher, maybe 115 for ABS prints to stick and prevent curling up at the 1st layers (you know :) )
    But it gets up to 102 very very slowly and cant get higher.
    It would drop down to 100 and slowly climb to 102-103 and drop again.

    Does that mean power supply cant handle it ?

    My Filastruder seem to have same issues, designers picked PowerSupply exactly to meet their needs, never 1 step above. Robo i suspect to be the same but i dont know.
     
  2. SteveC

    SteveC Well-Known Member

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    Tony, do you have the stock MOSFET on the RAMPS board? I swapped out mine for one with a much lower Ron and my bed will maintain 112C no problem with no print fan. The print fan will make it drop a few degrees but I usually don't use it because it frequently messes up the ABS anyways. See http://forums.robo3dprinter.com/ind...t-heat-bed-cutting-out.1299/page-4#post-23768 . I don't think mine can maintain 115C consistently though.

    I bed these bed temperatures depend a lot on the ambient temp (winter vs. summer) and if your printer is enclosed or partially enclosed. When printing with ABS I usually block the back of the printer with a metal box. Blocking the back may increase the thermal resistance enough to get your's up over 110C. Blocking the front will help even more.
     
  3. tonycstech

    tonycstech Active Member

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    i dont know what is MOSFET. Do you have a picture of it ?
    And can u give me full name so i can find it on ebay or something.
    Thanks !
     
  4. SteveC

    SteveC Well-Known Member

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    It's a type or power transistor that drives your bed heater. The replacement one is part number IRLB3036PBF. See the picture in the datasheet enclosed. In the RAMPS schematic it is called Q3:

    You can get it at Digikey or Mouser:

    Before replacing it make sure your RAMPS fan is working and air is flowing over Q3 and the yellow fuse next to it. If Q3 overheats it won't be able to maintain the bed temperature. I find that the new transistor barely gets warm. If you do decide to replace it let me know if you need advice on removing the old one.
     

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  5. tonycstech

    tonycstech Active Member

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    Awesome. Thanks !
    I have everything i need to get it replaced :)
     
  6. Mike Kelly

    Mike Kelly Volunteer

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    The issue isn't the power supply but rather the resistance of the bed. It only has 130w of power do it can barely reach 110c depending on your ambient temp
     
  7. tonycstech

    tonycstech Active Member

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    So changing the MOSFET thing wont help ?

    I wonder. Temp limit set to 120 or something by default but why if it cant get that hot to begin with.
     
  8. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Yes, it will help. Note @Mike Kelly said it can "barely" reach 110c (but it can reach it). If the MOSFET/s are acting up you will not even get close.
     
  9. Mike Kelly

    Mike Kelly Volunteer

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    Probably not. They just matter if they're tripping. The max temp is determined by the available power which is directly related to the resistance and voltage
     
  10. elmoret

    elmoret Filastruder

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    Correct, but with a lower Rds on the MOSFET, then you get a slightly higher voltage across the heater - so a little more power.
     
  11. Mike Kelly

    Mike Kelly Volunteer

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    That's a fair point. I should have taken that into account. Do we know the difference in resistance between them?
     
  12. SteveC

    SteveC Well-Known Member

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    • Stock STP55NF06L RDS(on) = 20mOhms Max at 25C, 5V GS
    • IRLB3036PBF RDS(on) = 2.8mOhms Max at 25C, 4.5V GS
    So that is about 7x more resistance at room temp. This normalized resistance versus temperature for the STP part looks a bit strange to me but the change over temperature looks like about 2x.


    upload_2014-8-3_22-39-52.png


    The IRLB3036PBF RDS(on) below might double over temperature too.

    upload_2014-8-3_22-41-42.png
     
  13. Island Bill

    Island Bill Active Member

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    Does the necessity of upgrading the MOSFET apply to the R1 shipped in August (all metal head, auto bed levelling)?
     
  14. Mike Kelly

    Mike Kelly Volunteer

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    I wouldn't say it's necessary, but if you're trying to push the limits of 12v might give you a bit more power output.
     
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