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A benchtop power supply is a handy piece of equipment to have around if you do a lot of electronics or other powered projects on your bench and need a reliable source of power at different voltages (+5V, -5V, +3.3V, +12V, etc). One option is to roll your own, using an ATX power supply yanked out of an old PC. There are a number of how-tos online for doing this. Several of the more popular ones are outlined below. If you want a truly safe, reliable, current-limited supply, a benchtop workhorse, you're best off buying a commercial unit. If you're just looking for 5V and 3.3V for the breadboard, the Maker Shed sells an awesome kit for $14.

Turn an ATX power supply into a lab PSU

Jason wrote: With a couple hours of work, it's pretty simple to pull the power supply from an old PC relic and turn it into a pretty decent bench system for powering your electronics projects. The standard ATX power supplys that you find in desktop computers have regulated 5 and 12 and 3.3 Volt outputs with sufficient power for most small project needs. You probably have a few of these just collecting dust in the basement, which means you could have a test bench PSU for quite a bit less than the 80 bucks you'd drop for one on
eBay.

WikiHow and Instructables both have a decent howto on the subject. As always, be careful when working with high voltage electronics. Nobody wants "almost saved $80" on their epitaph, so mind those capacitors.

Convert a Computer ATX Power Supply to a Lab Power Supply
ATX -> Lab Bench Power Supply Conversion

Here's the original article that inspired the WikiHow Power Supply.

Alden Hart, of Dorkbot DC and HacDC, has built a number of these ATX-based supplies. He writes: The ATX power supplies can be useful - 10s of amps of 5V and 12V, also 3.3V, -5V and -12V, if you need it. Plus, they usually come with a fan. But you may have plenty of these around the space already. You have to mod them to work in the absence of being plugged into a motherboard. There's a voltage sense line that's usually connected to a 3.3 V (or sometimes 5V) that needs to be connected, and they like a load on the 5V (10 ohm, 10 watt power resistor).

I don't usually bother with the binding posts and just leave the wires as long as I can and terminate in whatever power connector the project requires (usually the 4-pin floppy disk drive Molex connectors (+5V, +12V) because these can also be easily harvested and are cheap as connectors go).

If you want to buy a commercial benchtop unit, I know a number of people who swear by the models sold by Circuit Specialists. I haven't bought one of these PSUs from them, but I've bought other electronics equipment and have been very happy with their products and service. Two of my Dorkbot DC cohort have the same CS Lab Bench Power Supply.

Tim Slagle writes: I initially bought some ~$70 18V 3A power supplies with LCD meters on eBay (search for HY1803D) that were really too cheap.  They had a single-turn pot adjustment for the voltage that wasn't sensitive enough and would jump around as the voltage was adjusted.  And one of the three had problems with the current limiting, but the seller refused the package after I paid to ship it back.  I also found the 18V top end limiting as I had some LED lighting that needs 24V.

For the next round, I bought a 30V 5A supply.  The same one was available from different OEMs, but I wound up buying it from Circuit Specialists, the CSI3005X5, for $129 This supply is pretty nice, it has a 10-turn pot to adjust voltage, screw terminals for more permanent installations, and a bonus 5V@1A output on the back.  The current limit adjustment is a little awkward and isn't as fine as I'd like, so it isn't good for testing LEDs for example (I use the HY1803D for that). I also bought a 120V@1A supply from the same series which I haven't used as much.  It doesn't have the 5V@1A output.  I wish it went up to 160V or higher so I could use it for testing Nixie tubes.

BTW: Circuit Specialists has a long-standing deal where you can get a free DMM, plier set, or other swag with your first order. The MS8264 DMM is actually pretty nice as well, worth the $25 or so. [Gareth writes: I got this same DMM, free with a CS order. I thought it would be crap, and it sure feels cheap, but since one of the input terminals broke on my old meter, I've been using this one exclusively, and it's a lot better, more reliable than I thought it would be. The power of low expectations, I guess.]

DC-area artist, programmer and Dorkbot DC co-overlord Alberto Gaitán has the same CS unit as Tim. He writes: The CSI3005X5 Dual Output Bench Power Supply worked great for me when I needed a DC regulated supply to provide variable power to three stepper motors and three servos powering peristaltic pumps for 6-hours a day over four weeks for my Remembrancer (2007) installation. I also use it for 5VDC (fixed) applications on my workbench. I plan to be using it in this fall for another installation and this one will require it to run every day for up to six weeks.

Plug-in Bread-Board Power Supply

This power supply module plugs straight into common bread boards, allowing you to cleanly and easily power your board with a wall wart plug or with wires into screw terminals. It features a variable voltage regulator that can be set to output 3.3 or 5V with a jumper, or any voltage if a potentiometer is added. The input has a rectifier that accepts AC or DC (polarity doesn't matter)--just make sure the input is about 2V greater than the output you want. Skill level: beginner.

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More:

• Toolbox: Portable lighting
• Toolbox: Portable workbench
• Toolbox: From "miserable old box" to workshop showpiece

In the Maker Shed: Plug-in Bread-Board Power Supply