Prusa i3 MK2 Clone – Electronics – 24V Heated Bed Upgrade

I have changed my mind a few times about how I plan to finish off my Prusa i3 MK2 clone 3D printer… but now I have settled on a plan! None of it was particularly complicated, but I just want to arrange things in such a way that they are safe, tidy and give me the best result.

As I plan to add a physical brace to the Z Axis frame, I want to combine that with a suitable housing for all the electronics. With the actual brace made I can start finishing off the electronics!!!

There are few items I want to do:-

  • Fix the issues with LCD corruption – presumably cause by electrical noise
  • Remove the Polyfuses and provide alternative
  • Integrate the Raspberry Pi in with the other electronics so it is a permanent feature on the printer, including power
  • Add in additional temp sensors to the electronics and power supplies that will kill the power if anything looks dodgy
  • Power the Heated Bed with 24V instead of 12V – but keep this 24V separate from the RAMPS board

The last of these is the item I am doing first – and it the subject of this video.

The links I discuss in the video are:

Below is my rough schematic showing how I will wire the RAMPS, Arduino and also a small external board that will perform the heated bed power switching. Beneath that the calculations I made to conclude that the AUIRFB8409 Mosfet would work fine:

Rough Schematic of an external board to switch power to the 24V heated bed, showing relevant parts of the RAMPS and Arduino


Main considerations in choosing the AUIRFB8049 Mosfet, with calculations


  1. In your video you had a very interesting LIVE schematic of the circuit but I had hoped to see a link to the software on this page.


  2. hello, i have a lot of Mosfet IRLZ44N
    I want connect it to heat my 24v bed
    I understand how to calculate whitout heat sink but i can not understand how to calculate with heat sink.
    Can you give me the formula to calculate with heatsink?
    Keep posted the great videos, please

    • julesgilson

      January 20, 2021 at 5:27 pm

      If you mean how do you calculate what spec of heatsink is needed for the mosfet (if any), that is a complicated topic. There are three ways I know about: 1 – try it without a heatsink and see how hot it gets (or fails), 2 – same but with a commonly available heatsink, 3 – actually work it out… The datasheet for the mosfet ( will give the data on its temperature limits (175°C) and thermal resistance – but it is not simple and would take a long time to explain. I am sure it can be Googled. You don’t want to run it anywhere near 175°C!

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