Prusa XL heatbed MCU cooler - Programmable - STEP file included

This is a programmable heat bed MCU cooler.

This addresses a Prusa dev team design flaw for the Prusa XL. Once the printer is placed inside the enclosure, all kinds of issues comes with it. Extrusion issue and this MCU max temp  error that causes the printer to stop the print job. 

For those who didn't purchase the Prusa XL enclosure from Prusa, you will have to upgrade the following parts and print them in PC CF to prevent extrusion issues.

Idler lever A and B, idler nut, and idler swivel.

Next is where this MCU cooler come in. This keeps the MCU from over heating. Though Prusa's 6.0.4 firmware only addressed this issue with only a warning, but the location of the MCU directly under a heat bed is just begging for over temp errors.

update - 9/30/2024: Now includes STEP files

update - 7/30/2024: cleaned up screenshots and corrected wiring diagram

BOM: 

1x M3x40mm or longer screw

2x M3x25mm screws

3x M3x16mm screws

1x M3x6mm screw

2x M3 washers

1x Thermostat controller this link

1x 5015 blower fan this link

1x 14mmx14mmx10mm heatsink this link 

1x 25mmx50mm piece of kapton tape this link 

2x #8 spade connectors - best to have two different colors similar to this link 

1x 14ga wire about 18" (45cm)

1x 6" (15cm) heat shrink tubing for 14ga wires, electrical tape can be use instead

Tools:

Soldering iron, flux and solder

Wire cutter and wire striper

Heat gun (if heat shrink tubing is used)

Additional item: patience :)

Print the controller cover with paint on supports as shown.

Break off these 3 supports

Using 40mm M3 screw, attach the M3 nut to the end as shown and push the nut down into the M3 nut cavities.  Then unscrew the M3 screw once the nut is in place. Repeat for all 6 M3 nuts.

Place thermostat inside the cover as shown, secure the board using the M3x6mm screw. DO NOT over tighten the screw, then remove the protective film from the display.

Install the 3 M3x16mm screws then install the push buttons. 

Attached the main cover, then carefully flip the whole controller over and tighten the 3 screws (DO NOT over tighten)

Insert M3 washer through the M3x25mm screw then into the blower fan, rout the wires as shown and secure the screws

Wire preparation

Cut the wires for the blower fan approximately 7cm from the connector as shown

Cut the thermal probe wire approximately 10.5cm from the probe

Cut the wire of the thermal probe approximately 10.5cm from the connector

Insert heat shrink tube over the wires and solder the probe wires back together (wires are not polarized). 

Thread the thermal probe from the connector through the main cover and plug it into the controller board. Push the wire into the wire channels. 

Place the kapton tape over the probe to cover the metal part of the probe and trim off excess as shown.

Gently insert the probe into the main cover probe holder.

Attach the two spade connectors to the end of the 18" (45cm) 14ga wire, and solder a 2" (5cm) jumper wire to the end of the negative side of the wire. 

Solder the positive wire from the blower fan to the positive wire of the wire above.

Install the positive wire to the + terminal on the board and the other end secure it to the + terminal on the MCU's 24VDC terminal block. 

Solder a jumper wire to the negative wire, then Install the negative wire to the - terminal on the board and secure it to the - terminal on the MCU's 24VDC terminal block. .

Install the jumper wire to one of the load terminal on the board

Install the negative wire from the blower fan to the remaining load terminal on the board

Installing the MCU cooler

Power off the printer and disconnect the power cord

Install all 4 green retainers for the Z axis as shown

Remove heat bed and hang it on the left side of the heat bed frame

Remove original cover, loosen both positive and negative terminal screws.

attached the heatsink to the controller in the middle of the MCU board as shown

Attached the positive wire to the positive terminal, then re-tighten the terminal screws of and repeat for the negative terminal.

Install the MCU cooler cover with the same screws securing the old cover. Make sure not to pinch any of the heating tile cables. 

Reattached the heat bed, and REMOVE the four green stoppers.

Power on the printer, make sure the newly installed thermostat controller powers on.

Run Z-Axis calibration.  

Followed the included instructions for the thermostat to set your desired on and off temperature thresholds. Personally, I would recommend to 

Please note, there is a good chance this will void your warrantee, but you will have successful prints without dealing with MCU over temp errors. :)

Happy Printing :)