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Over the last couple months I've shared some nuggets of information here, on Twitter, and on Instagram, about my dc power distribution for my on-going shack build. I promised some more details, so here they come!
Pretty early on in the design of my shack, I knew I wanted to have a 12v power distribution arrangement of some type. The most obvious reason was because that's what most of our gear runs on, but secondarily, I wanted to make sure that some of my task lighting and other shack "appliances" are also 12v, so that I would have the option of some solar, battery-back up, etc. in the future. This dictated my basic requirements for dc distribution - a hefty power supply and/or batter charger, fuses or breakers for the different 12v circuits, and some basic control options (relays or switches) to turn stuff on and off.
Step 1 in this process - figure out what to mount all the stuff in! I personally like the look and workmanship of a proper cabinet and din rail. What I ended up using for the box was something re-purposed. I used to lug around some work equipment for training purposes, but with changes in products, and some abuse from being on so many planes, some of the equipment needed to be scrapped, so after gutting, I kept one of the back-boxes. To meet my power / future battery charging needs, I ordered a 75amp power supply/charger, and started with that:
While I can't help you out with sourcing a back-box exactly like this, I can share a link for the power supply. I chose the IOTA DLS-75 because they can be had relatively inexpensively, and for a large switcher, they seem to get pretty decent reviews from other hams in regards to being RF quiet etc. The model I got is a combined power supply / batter charger, so it will also cover me for future battery-backup when I'm ready to add it.
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This is the exact model that I picked up. You can click on the picture to grab one from Amazon, or if you're lucky like me, you might be able to snag one from ebay for a little bit cheaper.
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Next in line (because I like the tidiness that can be created using din-rail stuff) I ordered up some din rail and some DC breakers. To start, I grabbed a 63 amp breaker for the "main" a 25 amp breaker to power the main rig, and a 20 amp breaker to wire up misc. 12 v lighting etc. I also grabbed some bus-bar, and these nifty little din-rail mount plates to hold a raspberry pi and a couple arduino uno cards. The plan for these was to build in some power monitoring and logging. I also picked up a little arduino hat that breaks out screw terminals for the input and output pins, to make it easier to wire up sensors. It also gives a small prototyping area in the center, which may or may not be useful :-)
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Once I had this stuff and started wiring things up, I realized pretty quickly that I had a noisy fan in the power supply I got, so I ordered a replacement fan. At the same time, I ordered a couple other tidbits:
The little green thing on the right is a din-rail mount dc current sensor, good for up to 100 amps!
There's still a lot of bits I need to add, and wiring to tidy up as I do it, but as I started piecing things together, this is what it started to look like:
Wiring up the DC current sensor was pretty easy - feed it power with anything from 8 - 35 volts, and then read the voltage output from the sensor connection terminals. 2.5 volts is 0 amps, and up or down from there gives your your current in either direction (after throwing it into a quick formula to convert the voltage to current). Since this measures current in both directions, you could easily use this to monitory battery charging/discharging as well!
To monitor the main voltage, I just whipped up a little voltage divider to feed the arduino. Rather than use something specified somewhere, I just sat down with this calculator, and the pile of resistors in my junk-box until I found a combo I had that worked well. I then wired up the resistors into a harness, so the voltage divider is now in-line in the wiring between the the arduino and the bus bars where I connected to sample the voltage.
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With basic power and sensors wired up, I mounted up the front panel of the box, which has the display for the Raspberry Pi mounted to it. (If you missed it, I shared some info when I did that several weeks ago - you can check out the details here.)
Next, I whipped up some code! To save time for those who may feel this post is already getting a little long, I'll share the details on that code another time, but if you're super interested, drop me a note and I will send you copies to do with as you please. The quick summary is that I have the Ardunio reading the voltage and current sensors, and it dumps that data out of it's serial port. I then have the raspberry Pi running a LAMP stack. A Python script running on the Pi reads the serial data and stores it in a mySQL database so I can explore and manipulate the data it captures using all the mySQL stuff I'm accustomed to. I also whipped up a little PHP web site (only accessible on my local network at the moment) that displays the data. I have the display on the front of the power box showing the page in full-screen mode all the time, and I can also pull it up on my browser any time I want as well - it's fun to pull it up and make contacts while watching the numbers change :-)
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So there you have it - the shack power distribution update! There's still a lot of work to do on this, but at the moment I have functioning power for the rig and some task lights, and I'm recording data about my power usage. This means that when I get ready to drop some big back-up batteries on this situation, I'll have a good idea of what size of batteries to shoot for.
73 for now!
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