Improved Prusa XL Heat Bed Controller Cover - UPDATED V2

04/05/2025: Updated with a location to install a KSD9700 thermal switch to automate turning the fan ON/OFF as required.



09/06/2024: V2 now updated with sacrificial built-in supports to stop warping on the overhang while printing and added tips for multi material supports.

If you enclose your XL and/or live in a hot climate, it's only a matter of time before you hit a “MCU in Modular Bed is overheated.” error.

The MCU will error if it exceeds 100°C. It will pause the print and wait until the MCU temp drops below 82°C. When it does resume, a layer shift generally occurs, ruining your print.

When printing high temp materials with a bed temp of 100°C or more, my heat bed MCU would regularly see 86-96°C. Sometimes I would hit the ‘overheated’ error.

I live in Australia and my print room often exceeds 42°C in Summer. I have the awesome enXLosure from @Voxel3D , but any enclosure is going to create the same issue.

The ambient air temp in the enclosure doesn't get past ~40-50°C, so there is plenty of headroom for heat exchange.

Additionally, heat is the enemy of electronics, so the cooler you can keep them; the longer they will last.

I decided to add a heatsink and a heatsink to the MCU and 5015 blower fan. I remixed the original bed controller cover as the stock cover has very restricted/limited ventilation.

Hexagons were absolutely essential in the design, because everyone knows hexagons are bestagons!

Now when I print with a bed temp of 110C, my heat bed MCU doesn't get past 42C.

I have also added the option to print the numbers in a different colour that is flush with the face.

Printing:

UPDATE: I originally said that PETG is fine for this print. Additional testing has proven it is not. :(

A high temp material like ASA/PC, etc is required for this print due to the heat soak through the aluminium frame that the heat tiles are bolted to.

Load the XL Heatbed Cover 5015.3MF  file in the slicer and then right click on the model and select Add part>Load and select Support 1.3MF. Repeat this step for Support 2.3MF. You will see two ‘legs’ added to the overhang. These will stop the overhang warping at the end of the print. They get cut off with flush cutters when the print is done.

0.4mm nozzle
0.20mm layer heights
Classic perimeter generator (I love Arachne, but it sucks for thin walls and text)
4 perimeters
5 top and bottom layers
10% infill

5mm brim is strongly recommended to help with warping.

Paint on supports as show in the screen capture. Yes, you need the tiny bit of support exclusion (red) on the underside. It stops crazy supports being generated.

For best results, use the material you are printing the part with as the support material, but use TPU 95A or harder as the support interface material and set the Support material settings as per the screen capture. You supports will come off effortlessly and the underside of your part will look like it was printed on the print bed.

Turn on ‘Interface shells’ under Print Settings>Multiple Extruders>Advanced

If you want to print the numbers flush and in another colour, bring the cover into the slicer and then right-click on it and select Add Part>Load and select the Text.3MF file. Then all you need to do is select you need to do is set our extruder.

It helps to change the external perimeter width to 0.42mm and set a Speed modifier on the text and drop it to 25mm/s. This gives the best results for the qualtity of the text. Given where it is located, it doesn't matter too much if it isn't perfect and the defaults work fine.


BOM: 

• 1 x 24V 5015 blower fan
• 2 x 3mm fork red crimp terminals
• 1 x RPi/stepper driver style heatsink with a base of around 9x9mm to 9x13mm)
  e.g. 'Type B' from this link:
  https://www.aliexpress.com/item/32954848967.html
• 2 x M3 nuts or nyloc nuts
• 2 x M3 washers
• 2 x M3x22 or M3x25 bolts (If you user M3x25, you will need to print two of the spacers to stop the tip of the bolts sticking out the back of the mount, which will stop the mount from sitting flat)
• *Optional* KSD9700 40°C metal 5A NO (normally open) thermal switch. This will cycle in at 40°C and cycle out at around 30-35°C.
  https://www.aliexpress.com/item/1005005664797170.html
   

Assembly:

1. Turn the printer off.
2. Remove the stock cover.
3. Give the MCU a quick wipe with some IPA and then install the heatsink.
4. It is best to cut the wires for the fan short (just long enough to go into the cover) and then solder on larger gauge wire to make crimping the fork terminals on easier. You are looking for a total cable length of about 160mm.
5. If you are using the thermal switch, solder it in-line on the POSITIVE wire and then slide it into the retainers.
   
6. Install the fork terminals.
7. Insert the M3 nuts into the holes on the back of the new cover.
8. Pass the cabling through the hex hole below the fan mount.
9. Bolt on the fan with the M3 bolts and washers (and spacers if you are using M3x25 bolts), taking care to make sure it is hard against the side of the cover and is centred over the outlet hole in the cover. I deliberately used M3 fasteners to allow some wiggle room to achieve this as there appears to be a big variation in the accuracy and quality of mouldings 5015 fans.
10. There is 24V available directly on the modular bed card. Use the one labelled 10A. It make life easier insert the fork terminals if you remove the 10A fuse during assembly. Back the terminal screws most of the way out - they don't need to be removed completely. It is a little fiddly to get the fork terminals between the heatbed ring terminal and the washer - you just need to hold your tongue in the right position. ;)
11.  Tighten the terminal screws down and reinstall the fuse.
12. Install the new cover reusing the original bolts.
13. Job done!

As with all my designs, there are no affiliate links, etc. I get nothing out of them other than the satisfaction of helping the community and some Prusameters if you are kind enough to give my design a LIKE. :)

Happy printing and be sure to check out my other XL mods.

https://www.printables.com/@IPIND3D/models

1. Significantly improved ventilation. 
2. Added a mount for a 5015 blower fan. 
3. Added the option to print the numbers in a different colour/material
4. Fixed a bunch of jank geometry and poor face alignment. Seriously Prusa?!