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[GUIDE] Install a mosfet between the power supply and the heated plate

Why install a Mosfet

If you’re new to 3D printing and you’re deciding to buy a printer, or you’ve just finished assembling it, you’ve surely heard of the Mosfet, and you’re wondering: Why should I install a mosfet?

The basic idea is quite simple. The power consumption used to heat the dish goes all through the motherboard, and it’s not a good thing. All the power needed to heat the bed must pass through a single connector. This unique connector must also serve all other parts such as the hotend, steppers and logical drives. The standard connectors are then not sized and designed to be crossed by the energy needed to heat a 30×30 plate to 110°C. So if you want to deal with long prints with the hot plate or you are equipped, or sooner or later you will have to deal with a small fire.


Luckily when it happened to me, the fire extinguished itself. I wasn’t near the printer and there was nothing I could have done. Anyway after this experience I immediately wanted to install a mosfet to my printer!


Install a mosfet Install a mosfet


I talk of heated plate because it is the bed that requires most of the energy. The heating cartridge of hotends normally reaches 40w, more rarely 60w. The board as a whole needs another 50/60 w to power the microcontrollers and the display. Once the set temperature is reached, the energy required by the heating cartridge becomes intermittent and then decreases again. This brings the average consumption of a printer to work with the plate off to about 80/90 watts/hour. If our power supply is 360w (average size), then we see that more than 250w are hot bed paneling.

So by removing the bed current from the motherboard, you significantly reduce the stress on the motherboard connectors. If wanted we could install a mosfet for the Hotend even if with such low consumption I do not know if it is worth it.

Material required for this purpose:

Install a mosfet

For the installation you can certainly start by printing a special bracket to mount the mosfet attached to the card or separate. You can find lots of them on Thingiverse

NOTE: always check the polarities + and – on the cards.
* RED = + (on psu marked as + V)
* BLACK = – (on psu marked -V or COM)

Now act as follows:

  1. Disconnect the printer power.
  2. Remove heated bed power cables from the motherboard and connect them to the output power of the MOSFET unit.
  3. Connect the 2 wires from the motherboard bed output to the MOSFET control input.
  4. Connect the 2 wires from the PSU to the power input of the MOSFET unit.

Double check the diagram!

Even if the signal is said that it is not important the polarity does not cost anything to put it right, sometimes some mosfets are sensitive to polarity.

I hope that this mini guide has clarified some doubts both on the usefulness and on the installation of the mosfet. Electricity is no joke!

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