I’m not a big fan of computer power supplies but I had so many extra parts from building my other power supplies, I thought I’d give this a try. The only thing I needed to purchase was a couple of switches. I thought I could pull this off without any assistance but I seem to have run into something that don’t make sense.

I didn’t want to build your typical ATX power supply so I de-soldered all the output wires and only kept the wires I needed – 3.3V, 5V, 12V and ground. Here’s a rough wiring diagram.

PC PS 1 (resized).jpg

My plan was to run the three voltage wires to a 3 position rotary switch then connect the switch output to a terminal on the case front.

The voltages were a little low but I read that I need to add a 10 ohm – 10 W resistor to the 5 volt line. That worked fine as I now have the voltages I need.

The problem occurred when I tried to connect the rotary switch. When I switch from 12V to 5V or 3.3V to 5V the power supply kicks off. If I start at 5V it’s fine but when I switch to 12 or 3.3 it kicks off. If I disconnect the 5V wire and just have 12V – space – 3.3V it works fine. The switch is a “make before break” so I thought that might be the problem. So I opened the gap between the connectors but that didn’t help. The switch is a 4 pole so I moved the 5V wire to another pole and connected the 2 output terminals together. That didn’t help either. I have another switch (4 position – 3 pole). I connected that switch and still get the same results.

I’m out of ideas. Anyone have any suggestion?

Thanks

Bob

IMG_3357 (resized).JPG

IMG_3375 (resized).JPG

IMG_3380 (resized).JPG

switch (resized).jpg

pc box (resized).jpg

Thanks Mac, but I really wanted to use the switch. That's what makes it a little different and also will allow me to use the meter.

Wiz,

I did a bunch of test today. I’m sure my switch is the problem (make before break). If I just strike two power leads together I get the same results (power supply kicks off). I’ll order a new switch tonight.

I added a 10 ohm 10 watt resistor to the 5 volt power lead. That seemed to stabilize all the voltages.

Tony,

That’s a neat power supply. I saw it before. As a matter of fact that’s where I got most of my ideas for building mine. But I don’t like all the extra wires bundled together. I de-soldered and removed all the un-needed wires. I also connected the green wire directly to ground and use only one switch to turn on the AC power (through a fuse). I also don’t like all the power jacks. I know that limits me to just one voltage at a time but I don’t think that will be a problem. And I don’t like the looks of the ATX power supply box so I’m going to put mine in a plastic case.

Bob

That takes all the fun out of building a power supply.

My new switch came in today. This is what I ordered:

ebay.com link: 4 Pole 3 Position Rotary Switch Non Shorting RBS1 4

The ad says "non-shorting" but when I hooked it up it shorted my power supply - just like my other switch. I took it apart and I don't think it's "non-shorting".

IMG_3400 (resized).JPG

Looks like the wipper would connect two points at the same time.

I tried to open the space between the contact points (see the top of the wafer) to make it non-shorting but I don't think I should trust it.

This is the next one I ordered.

ebay.com link: Alpha 4 Pole 3 Position Premium Rotary Switch 1 Deck PC Mount USA SELLER

This look like it has insulators between the contact points. Hope this works.

My new switch arrived the other day. I hooked it up temporarily and it worked great. The new switch IS non-shorting. I decided to make a small PC board to mount on the back of the switch to make it easier to connect all the inputs and LEDs. It would also eliminate a bunch of wiring. After I etched the board, I tested it. It worked fine. Now all that’s left is the meter, power switch and assemble the box.

IMG_3415 (resized).JPG

IMG_3419 (resized).JPG

IMG_3422 (resized).JPG

IMG_3423 (resized).JPG

I finished up the ATX power supply and it works and looks great. Not your average looking computer power supply.

IMG_3433 (resized).JPG
IMG_3435 (resized).JPG
IMG_3441 (resized).JPG
IMG_3442 (resized).JPG
IMG_3443 (resized).JPG

On the scope it looks like a pretty steady voltage.

pic_68_1 (resized).jpg
pic_68_2 (resized).jpg
pic_68_3 (resized).jpg

In case you’re interested this is how it was made. Last winter I built a power supply especially for testing MPU boards. This is the build for that project:

https://pinside.com/pinball/forum/topic/meteor-resets-with-rottendog-solenoid-driver-board

So I had a bunch of parts left over.

Lately I’ve been messing with Arduino’s and they are mostly 3.3 volts and 5 volts. I had an old Dell power supply so about the only parts I needed were a couple switches. I didn’t want to use the metal ATX box so I made my own enclosure from some white Plexiglas I had. I removed all the unnecessary wiring to clean it up. I added the USB power ports for Arduino’s. The LED power indicators were completely unnecessary but they add a custom look.

IMG_3347 (resized).JPG
IMG_3361 (resized).JPG
IMG_3369 (resized).JPG
IMG_3371 (resized).JPG
IMG_3391 (resized).JPG
IMG_3393 (resized).JPG

This was a fun project – after I got the non-shorting switch worked out.

Thanks for the compliment and thanks for posting. I was beginning to think no one was watching.

It was a fun project. I really enjoy building stuff like this.

Bob