Replacing the PSU wires on a Prusa i3 MK3S

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I bought a 3DUPFitters acrylic enclosure for my Prusa i3 MK3S in an effort to make it a little safer. Even though I print with PLA, it can still release fine particles and VOCs that I’d like to avoid. The power supply that’s normally attached to the frame is sensitive to heat, so some users recommend detaching it and keeping it outside of the enclosure to extend its life. However, the wires that come with the printer are fairly short, which puts the PSU in an awkward position and prevents it from using the gaskets in the enclosure for routing wires.

So, I decided to double the length of the wires. Unfortunately, I made many mistakes when planning to extend the wires: I bought the wrong spade connectors (twice) and the wrong gauge of silicone wire. I hope this guide helps someone avoid the mistakes I made.

Materials

There are 3 wires between the PSU and the Einsy controller on the printer: two pairs of power wires and a power panic cable. To replace them, buy the following parts:

And have on hand the following tools:

PSU wires

Cut the 2 red and 2 black silicone wires to equal lengths, enough to reach from the Einsy board to the PSU through the enclosure. Unplug the PSU and unscrew the existing connectors from its terminals, removing the screws, and unclip the power panic cable. Make sure the #6 spade connectors fit on the screws and in the terminals, and then crimp two of them to the silicone wires. The side of the connector with the seam in the metal should be against the cavity of the crimp tool. Screw the spade connectors into the PSU, with the red wires on the positive terminals and black on the negative and the flange of the spades facing away from the terminal. Open the Einsy controller box and unscrew the PSU wires from the terminals on the lower-left hand side of the board. Make sure the #4 spade connectors fit on the screw terminals and then crimp them to the silicone wires. Run the wires through the removable gasket from the enclosure. Connect the pairs of red and black wires to the Einsy at the bottom terminals, making sure that the first and third wires from the PSU are connected next to each other. The flange of the spade connector should be facing up, towards the head of the screw.

Power panic wires

Crimp two Molex socket adapters to the two 22 AWG wires. Molex socket crimps have two sets of wings that wrap the wire: one for the insulation and another for the conductor. Crimp the conductor first and ensure the connection is solid by orienting the crimp with its wings facing the cavity of the crimp tool. With the wire and connector in place on the tool, press firmly to create a secure crimp. Only a wire’s width of conductor should extend past the wings. Use the smallest cavity on the tool that fits, in order to let the crimped wings wrap around the wire, instead of just its edges. Once both the black and white wires are crimped, slide the crimped wires into each Molex housing until the tab on the sockets snap into place. The white wire should be left of the housing when the plastic housing detent is facing down. Twist the white and black wires around each other to form a single braid of wire. Cut the wires to the same length as the PSU wires, and repeat the crimping process on the newly-cut ends. Route the wire through the removable gasket and plug one end of the wire into the Einsy board and the other into the PSU.

Cleaning up

Make sure the power cables function properly and run the printer through a heating cycle to make sure it can draw enough current through the wires. Feel the wires and make sure they’re not hot while in use. Remove the old cables and replace the cable management zip ties while incorporating the new wires. Make sure the new wires don’t interfere with the motion of any axis and that they’re not being crushed by the frame of the printer.