Building a bench power supply from a PC power supply is hardly an original idea, but it is a great idea. This idea isn’t even new for me. I built one before and decided I needed a second one.
Crappy bench power supplies cost around $100 on Amazon (I know I had one and it worked so badly I decided to build my first Bench PC power supply). You can build one from a PC for $10-$25 depending on how many parts you already have laying around.
If you are mainly going to be working with Arduinos you probably just need 3.3V and 5V and a PC’s ATX power supply will provide plenty of that. You can get used PC power supplies from your local used PC shop for maybe $20. Maybe you have one or more dead PCs already sitting around and you can just scavenge the power supply from it.
Besides 3.3V and 5V, a normal PC power supply will also provide 12V and -12V. A few will also provide -5V (more about this below).
Besides the published voltages, you can also get other voltages by connecting various voltages rather than the ground. The final voltage is determined by |v1-v2|. If you want negative, just swap leads. Here are the various combinations:
I decided to build a second Bench PC Power supply partially because I didn’t want to take my first out of my office and put it into the workshop. Instead, I wanted an additional power supply down there. PLUS when I built the first one I didn’t think I would need 3.3V and I really didn’t have room for the banana jack because of the way I built it, so I left off 3.3V. I would have been better off leaving off -5V or -12V!
-5V is kind of hard to find on ATX power supplies. But I really wanted it because I used it once before (OK, just once but maybe I’ll need it again). I had to do some searching to find one. In fact, I ended up buying a used version of my first Bench PC Power Supply because I knew for a fact it has the -5V line.
Any ATX power supply will provide +12, +5, +3.3, and -12V. If you, too, want -5V I can tell you this one has the -5V power rail:
It also has lots of room inside the power supply so it is possible to mount banana jacks directly to the case as the instructions will suggest.
Besides the power supply you are going to need a 10 ohm power resistor and banana jacks. These can be ordered from ebay or amazon. Further, if you want a power indicator you will need an LED and the necessary resistor to protect it. If you want a front mounted power switch, you will also need a small toggle switch.
When I built my power supply, I used these instructions:
They do a great job explaining the various steps so there is no sense in me being redundant.
On my power supply, I decided NOT to mount the banana jacks on the power supply this time. It was a pain to do that last time. Instead, I fashioned a U shaped panel out of thin gauge steel and mounted that to the front of the power supply. The banana plugs, LED, and switch were mounted to that instead of directly to the power supply.
This worked out fairly well, except bending the steel in a vise did not create a precise bend. It didn’t look too bad by itself, but once I mounted the steel to the case, it was obviously off a bit. I guess I’m going to have to invest in a cheap metal brake for whatever next project requires bending steel.
Still, the final product came out looking decent enough for the likes of me: