My Custom Power Supply (is complete!)
2018-10-18 18:29 - Making
You might not truly be an electronics nerd until you build your own power supply. Either way, I've finally passed that threshold. As I've mentioned previously (and previouslier), I've been working on mine — very slowly, off and on — for most of a year. The bare start came with a guide posted to Hackaday about using nichrome wire to heat and bend acrylic plastic in straight lines, to make cases.
I previously failed to bend the top correctly, and broke it in the process. I took more time, and made sure the folds-to-be were more thoroughly melted before pushing this time, and it came out almost perfect. There's one line in the top left where I melted the plastic enough to make a visible mark in the non-bent bit. (This is a fold down of the side. The holes on the top attach the side piece through this small folded piece.) I might have been able to avoid this, but it's only a small cosmetic issue, and more visible in pictures than in person.
The bottom needed work. I trimmed off bits of the sides to get the front lip to fold in, and later I ended up needing to cut off most of that lip. Some detail didn't go quite right in the planning and design. Worse, I got it left-right backwards. I chose plastic with a matte finish, but it is matte only on one side. I put the wrong side up (out) when cutting, so to get the matte surface on the outside, everything was flipped. This worked out mostly okay, but the (perhaps unnecessary) fan is blocked more than I would have hoped, and I had to extend some wires inside to make everything reach where it's supposed to.
The worst issue with the case is that I had barely experimented with the plastic folding, so I had to guess in a few places and didn't get what I'd have really liked. Some of the parts are located too close to the edge, causing a fold to warp or stretch inelegantly. I had to mostly guess about where the various surfaces would end up relative to each other to get things like screw holes to align. On the inner half, I made the screw holes elongated to cope with this, which ended up helping a lot later on!
The custom circuitry is really just this rectifier board. The diodes are tacked on the back — their leads are too thick to fit through the holes. The other side is stuffed full of capacitors, and another rectifier for the lower voltage half of the circuit, hooked to (I think) the transformer's center tap. That transformer was salvaged from a failed UPS. It's supposed to handle 1200 watts, so although I don't know its precise specs, I'm comfortable with what use I'm putting it to, here.
Things are getting more assembled here. The transformer is in place, and the rectifier board is nestled right next to it. On this side, it's brimming with capacitors (and one inductor) to smooth out the rectified AC voltage. There's hot melt glue everywhere. The fan is tucked behind the transformer, and at the left you can see the back of the plug/switch/fuse. I've been careful to heat shrink and/or hot glue exposed conductors. The bottom has slots for air intake, and you can see the extra cuts I've made, where things didn't fit quite as planned. After this point there was a significant delay as I decided to pause, to get black nylon (non conductive!) screws to assemble with. Then did it again when, only after receiving them, I realized the ones I ordered were too short to work for this.
The left picture above is near the final stage of assembly. In addition to two main front end units, I've also got a USB supply in here. It and the fan are driven from the lower voltage middle tap of the transformer. I tried my best to plan the mounting holes (on the top) and connector holes (on the side), but I was way off. At least one layer of plastic moved around in late design tweaks. So I ended up with these four little 3D printed brackets. Each is screwed into the USB supply board, dropping it quite a bit lower and moving it back a smidge, and those get screwed into the top of the case. This unit displays the voltage (not so useful unless you're drawing so much current it sags?) and the current being drawn. And it constantly flips back and forth. I was concerned that the blinking would be annoying. I tried to address that by sandwiching in a smoke-colored only-mostly-transparent piece of acrylic between it and the world. Due to these brackets, it ends up only being visible from just the right angle, so the blinking display will not be an issue!
Here's the final product. There's two RD Tech 5005 (50 volt, 5 amp max) units on front. Each is wired to a pair of both binding posts and banana jacks, so I can hook pretty much anything up. The fan exhausts out the back, next to the power plug, with switch and fuse integrated. On the right side are the USB connectors which took those brackets to line up, here a fan is plugged into one of the two ports. If you look down from the top, you can see the USB supply's display, in this case showing half an amp being drawn by the fan.
The top clearly doesn't line up perfectly with something else, so it's bowed a bit. Assembling the case, and getting all the screws to line up and mate with the nuts inside was very difficult, so I'm not going to open it up and try to fix this unless something worse than cosmetics goes wrong. Look closely around the power plug, and you can see that I bent the edge out from beside it, because the hole was too close to the edge being bent. A bunch of extra hot melt glue helps the plug stay put, as a result. The same sort of (unavoidable, in this case) thing happened at the front: the supplies each have a USB connector beside them, which can be used to log data and set settings via a computer. The hole for the connector must be right next to the mounting screw holes, and so each of them ended up puckered along the folded edge.
I'm really happy with the angled front, which makes the displays very readable from a normal sitting position. And I'm extremely happy that I've finally taken this project through to completion! Learning how to melt and fold acrylic opens up all sorts of opportunities.
