Astro Pi Power Bank

This battery box is my solution to portable astrophotography. It is designed around a 12v 180x175x75 mm, 240AHr LiFePo4 battery. It is design to hang by the carry handle under my telescope mount.

The large (28mm) circular holes are sized and spaced for standard switches and accessories sold for cars and boats. You can fit what you like. My setup is the following:

The front panel

• RPi4
• 3x DC 5.5mm power sockets (8mm diam)
• Voltage display
• USB power sockets

The rear

• Main switch to isolate all electronics from the battery.
• 12v Socket - for charging the battery and as a DC power port.
• 2x fuse holders
• Accessory power switch
• Raspberry Pi Power Switch

I have allowed for two fuse holders, I only use one, the second holds a spare fuse. 

There is a drive bay enclosure on the top of the box to hold a portable SSD. The bay is a separate item and could be replaced by a simple handle.

Materials

• Box Top and Bottom: PETG recommended (I used PETG-CF) PLA will work but is brittle.
• Top drive bay SSD enclosure: PETG - I used transparent PETG so I can see the SSD drive light flashing.
• Strap and Peg : TPU 95-A. 

Construction

The top and bottom parts slide together. The battery is heavy so for security I use 4x M3 nut and 16mm M3 bolts to clamp the two parts.  If the nuts are loose, fit the nuts, thread in the bolts and then fill the side holes with hot-glue.

The front panel is bolted to the case using 5x M3 inserts and 5x M3 6mm bolts.

The drive bay is bolted to the top case with 4x M5 16mm bolts and 4xM5 nuts. The nuts should push-fit into place but if they are loose use some hot-glue.

To fit the carry-strap, push it into the slots of the drive bay and then push the TPU peg into the slots of the strap. If you don't trust TPU for the pegs you can use a zip strap.

There should be 3-4mm spacing around the battery, fill it with some packing foam.

Printing

I don't think it is critical but I used 0.28mm layers, 4 walls for the box and 15% infill. The strap was printed with 10% infill.

This box is about as big as my build plate will allow. The edges of my build-plate are a little cooler so I used a brim to make the corners stick down well.  After printing I sanded the tongue and groove features to make sure the top and bottom pieces slide smoothly. Its designed with 0.3mm gaps.