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VoltMeister 100: Bench Power Supply - Part 2

26 November 2014

In Part 1 of this article I’ve discussed the design and PCB layout for my VoltMeister 100 project. I’ve converted an ATX power supply to a safe-to-use bench power supply. Although not ideal for anything serious, it’s a great way to actually get started and complete a project.

This is Part 2 of a two part write-up of how I designed and built my first bench power supply.

The enclosure

I think that in a professional design process there is some tension between the PCBs you design, the components you use and the enclosure you need to all fit it in. I tried to be smart and opted to buy a ‘universal enclosure’ that would fit my ATX power supply and leave some room for a small PCB.

Because of the dimensions of the ATX power supply (roughly 140x50x80mm), I needed something that would fit that. Note that most dimenstions specified when shopping for enclosures are outside dimensions.

In the end I opted for a nice Hammond enclosure, large enough to fit my power supply snugly and not too expensive. It even has nice aluminium front and back panels. For those wondering, it’s the 1598ESGY from Hammond.

Another thing I learned is to take a detailed look at the specification drawings.

Notice the two supports circled in red? Yeah, those are used to screw the top and bottom parts of the enclosure together. And guess what, my ATX power supply does not fit between those two supports and is now protruding about 10mm from the back. Booh!

This is really a problem. I don’t want to have an ATX power supply hanging out of the back.

At first I thought of just buying a larger case, but I would not be that easily defeated.

Because I’m curious by nature, I opened up my ATX power supply to see what’s inside and remove some of the cables I would not need.

The PCB for the ATX supply is pretty tightly packed, but I noticed that transformer on the side was not mounted on the PCB. There was a nice cutout on the PCB to allow room for the transformer.

Putting one and one together I decided to remove the ATX enclosure and see if I could fit the PCB in my small Hammond case. The transformer could be moved just a bit so it would not interfer with the support inside the case.

This worked brilliantly. All I had to do was make cutouts for the powercord and 120/230V selector.

The only reason I did this is because there is a clear separation between the high voltage parts of the supply and the control (for the fan, I presume). Because the orientation was just right, it would also shield my own PCB nicely.

The build

Here you can see the inside of my bench power supply.

The bottom half is filled with the ATX PCB. You can see the ground wire floating around, this has been connected properly tot he front and back panels.

The transformer is leaving a bit of a gap and has been placed just on the other side of the support.

On the top you can see my PCB with the ATX connector attached to it and wires going out to the LEDs, the power switch and the different output voltages.

The result

And, this is the end result. Suffice it to say that my precision drilling skills need some more love. But other than that, I’m quite happy with how it turned out. It’s my first project, after all.

Conclusion

Building an ATX-based bench power supply like this is nice. If you need a stable and reliable power supply, you’re probably better off buying a cheap linear power supply online for like € 50.

I did this project to learn something. And I did. I learned how to SMD solder components, I learned what to look out for when selecting an enclosure for your project. I also learned about ATX power supplies and how you don’t want to mess with them. These units handle pretty beefy currents. If you don’t know what you’re doing you could end up hurting yourself.

What’s next? The VoltMeister 200, of course!