Saturday, July 25, 2009

Power Supply

Here's a little project that I've been meaning to get to since before the big move to the new house - building a benchtop power supply out of spare computer parts. Why build a power supply? Good question - lots of answers:
  • The only motorcycle battery I currently have is in my running Kawasaki Vulcan. I don't really want to spend time disconnecting the battery from that bike just for bench testing (there is no way that I would test stuff while hooked up to my bike).
  • I would rather not have to fool with recharging a battery just for testing
  • I've been itching to solder something and do an electronics project.
  • If I really mess something up, the power supply is smart enough to shut down rather than fry itself. If I cross the leads on a battery, ouch (I've heard that it's like crossing the streams).
  • This power supply also outputs +5v and -12v. I'm sure that will be handy for an electronics project sooner or later.
Behind every great project (and even mediocre ones like this) is usually list of semi-willing contributors:
  • Chris H for providing phone support while in Radio Shlock picking up parts (the power resistor worked like a champ).
  • Tim M for providing the donor power supply.
  • Ulysses and Wendy for the gift certificate that bought the heat shrink tubing.
  • Mr Barrowman for letting me play with breadboards in Technology class during the formative years.
Turning an ATX power supply into a benchtop power supply has been done many times by people who take much better pictures than I would, so here is what I used (there are many available online, but this is what I stumbled on):
  • This was a nice simple post on to build the unit. It even had some notes for making a more simple setup (no switches, LEDs, etc).
  • Instructables via Make - This was an okay set of instructions, except for a few key issues (the plan was more complicated than I wanted - I just wanted to plug it in - no switch necessary). More importantly, the plan called for a fused ground (readers tore the author a new one for that in the comments). That's not a safe / cool way to fuse a circuit, so I didn't do that.
Things I Learned
I always learn something from these projects.
  • I really need a better soldering iron. I still have my old nasty 30W pencil from Radio Shack. Specifically, I need something that I can rank up the heat on for soldering larger gauge wires. Make has had a lot of articles about just this sort of thing lately.
  • I need a better soldering station. I'm using an old sponge for cleaning and a screwdriver rack to hold my iron. It's neither safe or efficient.
  • Heat Shrink tubing is just cool as hell. It really makes a project look nice and neat. I think that it's a bit more robust than electric tape as well.
  • I should have drawn the circuit before I started. It was a dirty simple setup, but drawing it out would have saved some unbundling of "unused" wires. My workbench is a whiteboard, so there's no excuse there.
  • I should have saved the rest of the computer that I pulled the power supply from. It had handy things like LEDs that would have made the project look a little more nifty. Although it should be noted that it's pretty obvious when the power supply is on because the fan is louder than hell.
  • Wearing eye protection while drilling isn't as dumb as it sounds. My drill bit caught and spun the power supply around while the wires whipped around and broke one of my favorite Coke glasses. Darnit.
It looks like the "cool" way to build the unit is to stick the fan on the outside of the power chassis. I didn't really need any extra room on the inside, so I just left it where it was (the wires for the fan were pretty short anyway so this was the lazy option).

Now I can get to work on getting some of the basic electronics kicking on the bike (signals, brake lights, etc).

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