Electronics Box for Original Ender 3 motherboard and BTT 24V UPS v1.0 with ON/OFF switch

Background:

I thought I had damaged the BTT E3 Turbo board in my original Ender3 printer, by repeatedly printing models in ASA with the printer zipped into an enclosure.   (As it happens, I later traced the problem I was having with Klipper shutdowns to a different source, so the Turbo board is probably now a viable “spare”.)

I have “killed” several BTT boards over the years, always from a TMC motor driver failure, and usually traceable to an aluminium heatsink coming loose (unnoticed) from the driver chip.  

This time, rather than risk damaging the replacement BTT SKR Mini E3 v3.0, I committed to moving the electronics remote from the printer and so created this box to install the new board under the IKEA table on which the enclosure stands.  

I seized the opportunity to also install the BTT UPS in the same box.  Then I added an SPST ON/OFF switch, so that I can disconnect the UPS when I want to cycle power on the printer (e.g. for flashing firmware).  I already had one of these switches on-hand that I bought in error for a previous project, so I designed the box cutout to fit.

Since I run my original Ender3 on Klipper with a 7" tablet and Klipperscreen, I decided to abandon/retire the original 12864 screen.  That gave me the freedom to mount the electronics and Meanwell PSU under the table.  I “just” extended the printer harnesses (heater cables, thermistor cables, motor cables) enough to reach their destinations inside the box. 

WHICH BOARDS DROP-IN TO THIS BOX?:

I spaced the installation standoffs precisely per these BigTreeTech diagrams for the two PCBs:

1. BTT E3 SKR MINI V3.0_SIZE_20220301.pdf
2. BTT UPS 24V V1.0 Manual-2019-11-29.pdf

Any board designed to drop into the original Ender3 box should also therefore fit into this box. [e.g.  I know that my “ex” BTT SKR E3 Turbo fit and that was a bit over-sized, compared with the stock Creality board and the BTT SKR Mini E3 v 3.0.]

THERMAL INSERT TIPS:  

All of the standoff holes - and the four tabs that hold on the box lid - are designed to hold M3x4.2x6 or M3x4.2x4 brass thermal inserts like these.

I am no expert with thermal inserts, but I have posted pictures showing my technique, and I did succeed by building my own box this way.

1. Install a bolt of the same length into the insert, before placing the insert into the target hole, to prevent molten plastic from pushing up into the insert when you push the insert into the standoff.
2. If you are using a soldering iron to heat the insert, be sure that the tip fits into the hole in the top of the bolt, and is tightly fixed to the soldering iron, so that you can maintain a light vertical pressure on the insert.
3. Just as the plastic starts to melt, the insert may start toppling over, rather than descending quietly into the hole. Be both patient in easing the insert into the hole and alert enough to pull back and readjust, if it starts to topple.
4. Lower the insert until the bolt head reaches the top of the standoff.  Then remove the heat.
5. When installing the boards and lid, be gently when torquing the bolts, to avoid placing unnecessary stress on the insert.

[NOTE: My printer may not be perfectly calibrated to print holes precisely enough.  I had to ream out the mouths of my post holes with a 5/32" (3.97mm) drill bit, to be able to stand the 3.7mm inserts vertically in the post holes, so that I could use my hands to hold the box and the soldering iron.]

SOME BOLTS REQUIRED:

I have a box of M3x6, M3x5 and M3x4 bolts, with which to install the boards.  If your shortest bolts are M3x8, you might want to increase the height of the mounting posts in the .f3d file (e.g. to 9 or 10mm.  If you choose to do that, remember to also offset the USB and SD card slots an equal amount higher from the bottom of the box…)

If you prefer to use M2.5 bolts and inserts, you will want to resize those post holes to a smaller diameter, by 0.6mm.

WIRING TIPS:

I took time to loom the wires inside the box, so that they run either side of the mainboard and do not cross in front of the fan, as they always did in my original printer box.   I was planning to use that spiral conduit to hold the harnesses, but instead resorted to using tie-wraps.  Not sure whether that was a better choice.

FAN TIPS:

The integral air grills - placed at the motor driver side of the box and at the UPS end of the box - also help the new 6020 cooling fan to keep the relocated system very cool.   [I feel a cold draft coming from the box, when I am sitting in front of the printer table…]

I tried installing the 6020 fan inside the box, but found that the fan body actually fouled the aluminium heatsinks on my old E3 board.  Rather than press the fan up so tightly against the board, I elected to mount the fan outside the box, blowing inward.  If you choose a 6010 or 4010 fan, you could consider putting the fan inside (or you could make the box taller, or make the lid deeper…)

NOTE:  The 6020 fan in my design is so over-powered that when it was triggered based on bed temperature, it drove the MCU temperature below 10 degC and shut down my print. 

I have since added a lid remixed for 40mm fans, in case you prefer to go that way, as did I.  

I configured Klipper to use my fan to maintain a target controller mcu_temperature of 35 degC, as follows:

[temperature_fan controller_fan]
pin: PB15
sensor_type: temperature_mcu
min_temp: 5
max_temp:100
target_temp: 35
control: watermark

NOTE: I deliberately installed the fan nuts to hang outside of the box, just to mitigate the risk that one or more nut might someday vibrate loose.  At least this way, it will not go unnoticed.

BOX MOUNTING TIPS:

The four tabs on the “bottom” of the box, are designed to let me screw the box - upside down - to the bottom of the table.  [Based on the fan noise that is now transmitted to the table, I suspect it should be mounted with silicone spacers or a sheet of fun foam, to make it a bit quieter…]

I was initially inspired by the design of this box: https://www.printables.com/model/198257-ender-3-electronics-box-for-btt-skr-mini-v2-and-ra, but you will notice that there is not much in common between that model and this.  

I designed and modelled this box from scratch, in Fusion360.  I have uploaded the .f3d file to support anyone who wants to customize this design to their own taste/requirements.