I have a DIY 3D printer. Everything works fine except the heated bed. When I plug my heated bed to the D8 terminal smoke comes out.

This is my third RAMPS board that I have had this problem with. After it burns the RAMPS still works but the heated bed doesn't stop to heat. I am using a 12 V 30 A power supply.

Is it something about my power supply?

Annotated RAMPS board showing hot areas

  • 1
    $\begingroup$ We will need some more details on the heated bed you're using and how it is connected. The RAMPS can only handle around 11A for the heated bed. Maybe your bed draws more than that? $\endgroup$ Commented Aug 12, 2020 at 8:57
  • $\begingroup$ It's probably not the power supply. Please measure the resistance between the two wires which lead to your heated bed - perhaps there's a short which causes an excessive current draw. It's also usually recommended to use an external MOSFET for the bed - which is easier and cheaper to replace than the entire RAMPS in case it fails. $\endgroup$
    – towe
    Commented Aug 12, 2020 at 9:10
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    $\begingroup$ my bed is 1-1,2 Ohm. Its drawin too much current for ramps. I will use externel Mosfet. Can the externel Mosfet stands my power supply? Its 30A $\endgroup$
    – turguttak
    Commented Aug 12, 2020 at 9:39

1 Answer 1


It could be a couple of issues:

  • the heated bed tries to use more power than the ramps board is capable of because the traces on the board aren't big enough to get rid of the heat.

  • the thermistor is broken / not properly connected or configured, and it keeps on heating the bed forever.

  • a short somewhere in the wiring.

My advice:

Check the wiring. If there is no short, check your thermistor. Is it reporting the right temperature? If it reports the right temperature, try using a external mosfet module for the heated bed. These are fairly cheap, and easy to connect.


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