Building a Power Box for a Telescope

The more automated my setup has become, the more cables it requires and it has now got to a point where I want to simplify my set-up. The first element is therefore to build a future-proof power unit to mount on the scope and power my focuser, cameras and USB hub, all of which run off 12v. I also want to power my Canon DSLR, which runs at 8.2v, off the same unit. The whole system needs to be light enough to mount onto a scope and not affect the weight. I also need to design and 3D print a mounting system for each of my scope tubes.

Tools:

  • Soldering iron and solder
  • Pliers
  • Drill and appropriate bits
  • Cable stripper and crimper

Parts:

  • Weatherproof junction box (200mm x 120mm x 175mm)
  • Universal blade fuse 6 way box
  • GX16-2 Aviation 2 pin Connectors (5A rated)
  • Buck converter to step down voltage
  • 16 AWG wire
  • 12 AWG wire
  • 5.5mm x 2.1mm Male and female DC Power Plug and connectors
  • Heatshrink Electrical Sleeves
  • Electrical crimp connectors
  • 20A Bus bar power distribution

Skills:

  • This involves a fair amount of soldering so knowing how to solder well and efficiently is an advantage. 
  • You also need patience – test everything twice before moving on. The whole project probably took me around 6 hours.

Process:

I mounted all the components I needed into the junction box using plastic spacers and superglue, ensuring that there was room for the wires and that I always had a clear idea of the flow of current through the circuits. The 12v input went straight into the 5A fuse box before running 5 outputs to the aviation 2 pin connectors. I opted to keep left positive (looking from the outside into the female connection) – and then ran the outputs of each of those connectors onto a bus bar before connecting back to the DC output (another aviation plug).

Components in place
The buck converter is on the right (with the heat sinks); the fuse box is on the left at the back (no blade fuses in yet). I added the full bus bar in at the end of the project (where all the negative cables are joined on a single bolt for testing).

The 6th output from the fuse box went into the buck converter to step down the voltage from 12v to 8.2v to match the Canon’s power requirements. It is worth spending a little money on this buck converter as you don’t want it fail! The output for the DSLR is a more simple 5.5mm x 2.1mm power plug.

At every stage, I tested the circuit using a multimeter to ensure that I wasn’t mixing up any polarity or pushing out too many volts. Only once everything was tested and re-tested did I make up the cable lengths I needed to connect to my 12v items. I used the 16 AWG wire for this as it will easily deal with any current – on one end I put a DC power plug, and on the other a male aviator plug that can screw into the connectors on the box.

Internal wiring
Here we have all the internal wiring complete, and ready for testing with the multimeter.

For the DSLR, I had an existing dummy battery from an AC/DC power unit that I simply cut and attached a DC power plug onto. I again re-tested this before putting into the camera for a test.

DSLR test
A successful test on the DSLR powering up!

I have 3D printed a mount for one of my scopes to allow me to attach it using velcro, and have also used velcro to attach my Moonlite focuser control, and a 7 way USB hub, to the outside of the box.

Each of the connections is fused at 5A to protect against surges – there are more fuses at the power end of my system for redundancy. The next step will be to connect up all items on my scope and run a full stress test, using a power meter, to see how much current is being drawn. I estimate even with the TEC cooling running to keep the camera -30c below ambient, the power box will draw less than 5 amps total. 

power_box_wiring
The completed circuits inside the box. The input connector is on the right hand side. The bus bar is now in place front left.
power_box_finished
The finished box with a pen for scale

Currently I will power this via a cigarette-style 12v plug (as seen on the power cable). Eventually, and depending on the maximum amps drawn, I might remove that and connect to the 13.8v DC bench tester itself via a second buck converter (to reduce down to 11.8v). 

Once I finalise my mounting options, I’ll update with more images.

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