A PC-PSU (ATX) based lab power supply, the umpteenth version... - Page 1
Forum section: electronics / projects

author: kjs
author_rank: Regular Contributor
timestamp: March 03, 2015, 06:45:49 am
content: Power supplies seem to be always in short supply and here it isn't different. That's why I needed yet another power supply (one? NO: 4!) and as I didn't want to buy these really low end Chinese ones (low current and quality?).To keep the expenses low I decided to modify an ATX PC-PSU as it would give me the most used voltages (-12, -5, +3.3, +5 and +12V) at decent current levels to also use it for designs with high power requirements. Best thing is that I have several of these on the shelve which are no longer good for the power hunger today’s PC's and graphic-cards develop. There are multiple instructions on the web how to do it but I made it a bit different which is the reason I post it here. I just didn't like the idea of a separate box or the binding posts directly in the PSU case without fuses. Cheap doesn't mean that it is allowed to be dangerous or not practical.....This may also make a nice project for someone with little money in need of a decent power supply with multiple voltages.Note: some PSU's designed to the latest specs no longer provide the -5V. Just check on the label and you will know. The white wire however will still be there so don't rely on that......The outputs are all via individual fuses with failure indicator LED's, the output is switched and there are LED's for ON and standby. Everything is on an add-on front panel mounted with standoffs to the PSU. The unit also has an extension connector which I will use in the future.All parts can be found for cheap on ebay or aliexpress. The worst part of building one is to wait until the parts not in stock arrive via snail-mail from China (usually 3-8 weeks)....... That much for a quick and dirty solution!In case the PSU fails in the future it's an easy task to transplant the entire front panel onto the next one (I still have seven out of old PC's on my shelve. Tendency: growing).As posting the complete write-up here would be too much hassle especially due to the many pictures I made a PDF from it and host it. You can find it here:http://www.pinzi.us/RS-E/download/RSE-PSU-LAB.pdfIf you have any questions please feel free to ask! I'm not here every day, some work gets into the way of pleasure, so please be a bit patient (or try my email)......A short explanation why the write-up is on “company paper”: when we build something for internal use it gets a part-number and the “how-to” is stored on the server. When someone wants their own they know where to look and don't have to bother you. Plus if a customer insists to get one of these “few-offs” (most likely not in this case) we already have some paper we can hand out. As I also wanted to post it here I wrote it a in a different style than usual but it still serves the original purpose. It's also hosted on my private site in addition to the "official one"....

author: paulie
author_rank: Frequent Contributor
timestamp: March 03, 2015, 04:33:12 pm
content: Very nice. I've always liked the 2nd front panel approach but took it a bit farther by using a motherboard connector so there are no modifications needed to the PSU at all. Saved having to build a new unit when accidentally shorting the wrong wires. Those fuses don't help at all there.Another difference, in addition to bringing out the voltages I use a $2 Ebay adjustable buck-boost for 0-40v at couple amps. Also previously a $1 three digit voltmeter but now use one of the 5 digit ($3 and change) switchable for precision volts and current. No op amp or costly shunt required thanks to the higher resolution.

author: kjs
author_rank: Regular Contributor
timestamp: March 03, 2015, 07:19:45 pm
content: the buck boost is already done but needs a bit more testing. That's why this thing has the extension connector. I'm also at a version which has a USB interface but that won't be done in the next few weeks due to other priorities.In my case the fuses helped already (I used fast blow ones). Without them I am sure one of the PSU's would already be blown instead of just the fuse. It may also well be the type of PSU and I am sure that there are many which are build pretty lousy.I thought about using the connector but the wires are that long that the front panel would have to be on 20" extensions.