A Tale of Two Power Supplies

Staying Safe in Your Hobby Projects

Today we diverge from our regularly scheduled PC hardware and will crack open a pair of benchtop power supplies. The reason? A common trait among PC enthusiasts is that they rarely have just one hobby, and the other hobbies often involve wires. A cheap, low-voltage power supply is a handy addition to the workshop.  But, with the modern gray market being what it is, safety concerns abound, and we have found a couple big ones in today’s subjects.

We also diverge from our standard review format and offer not one, but two convenient options for your consumption. First, we do have the usual text review and photos. But we also offer a feature-length video presentation entitled “Two and a Half Power Supplies.”  It boasts additional content, flashy visual effects, and 20% more sardonic commentary. Check out the independently produced YouTube feature for the video option, or continue reading below to do this the traditional way.

Yes, you are seeing that correctly: TR is hosting a video feature.

The TechReport’s gerbil community embraces a diverse mix of hobbies (link references a thread on TR’s forum.)  Many members are engaged in self-performed home improvements. Some have interests in do-it-yourself (DIY) audio technica, and there is also a long-running thread for remote control aircraft and related hobbies. Raspberry Pi, Arduino, and other microcontroller questions pop up from time to time. More recent topics include 3D printing and piece-wise restorations of classic arcade equipment. Photography is recurring, often intersecting with the others for obvious reasons. Some of these pursuits are benign as regards electrical safety, but others expose the user to hazards.

A TR Forum Gerbil

A TR forum member, standard model and options.

A traditional PC hobby is relatively safe. The desktop power supply is typically a certified Class 1 appliance (link references Wikipedia). That means the high-voltage bits are enclosed by a metal chassis with a dedicated safety ground wire, a kind of electrical restraining order in case a live wire has the urge to reach out and touch something. Small-form-factor and laptop power bricks sometimes have a ground wire for RFI/EMI suppression but are usually built as Class 2, or double-insulated, and can safely operate with no ground wire connection. The output side in either case is isolated from the high voltage side and operates below the generally accepted high-voltage threshold of 50 volts. As such, the user is not at imminent risk for shock or electrocution.

Power Supplies

Typical PC power supplies. What’s an “OCZ?”

Of course, there is always a way to start a fire if the user tries hard enough. As the saying has it, anything made idiot-proof only engenders better idiots. In general, though, the combining of safe power supply design with standard plastic connectors has made a DIY PC hobby relatively accessible.

Disaster Girl meme

UL Certifications? Nope, haven’t seen any.

New equipment in the US and Canada is usually compliant to the electrical safety standards of Underwriters’ Laboratories (UL) and the Canadian Standards Association (CSA), among others, and some of those labels will feature prominently. Globally, many other standards apply, and since electronic hardware is often sold internationally with universal input voltages, it’s now common to see a bevy of certification labels on electronic equipment.  Witness the awe-inspiring Rosetta Stone appearing on the side of this ordinary laptop power brick, for example:

Laptop power brick

The usual hieroglyphics found on modern, globally sold equipment.

Unfortunately, all that goes out the window when gray market hardware enters the picture. Direct-import kit is readily available from the usual online portals, and it sometimes appears in local hobby shops and other independent retailers. Direct-import kit often fails regulatory tests in the countries where it lands, even though it may attempt to comply, or display counterfeit labeling. For a little light reading, check out this very spooky UL report on counterfeit i-device chargers (link references Underwriter’s Laboratories). Gray market sources for used equipment can range from online auctions to local surplus shops and private yard sales. Whether old or new, gray market equipment can harbor serious safety problems.

In order to demonstrate the effect of all this, we will evaluate and test two useful, 12 VDC, benchtop power supplies from the gray market. 12 VDC nominal (13.8 VDC maximum) has been a standard in automotive electrical systems for more than 60 years and there is plenty of 12 VDC equipment that someone might want to test or power indoors: scanner radios, drink coolers, small tire inflators, charging devices, car A/V accessories, or even vehicle components such as lights, sensors, and accessory motors. Many LED lighting products are available at 12 VDC, too.

Computer peripherals are also commonly 12 VDC rated. Due in part to its automotive origins, 12 VDC was in wide use when IBM developed its first desktop PC and a 12 VDC rail was provided in that system to power motor loads including fans and disk drives. Desktop computers still use it today, albeit indirectly, since everything operates through switching converters. Some people have correspondingly hacked out 12 VDC bench supplies from spare PC power supplies, but with the modern ATX standard this requires managing a couple control pins.  The basic hobbyist might prefer something ready-made, but then unwittingly purchase the electrical version of Pandora’s Box.

Disclaimer & Warning

Only a qualified person, meaning someone who has the correct training and tools to work on high-voltage equipment and assumes the risks of doing so, should be opening or modifying the equipment discussed in this article. Neither the author nor the Tech Report warrants this information for accuracy or completeness. We do not encourage you to open or modify mains-powered equipment and will only do so here for investigative purposes. The data and techniques reviewed in this article are for informational purposes only, and you alone are responsible for anything you do with them.

With that said, let’s look at two common options and assess their hazards. Next stop: Power Supplyville, population: Us.

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Aaron Vienot

Engineer by day, hobbyist by night, occasional contributor, and full-time wise guy.

35 Comments
    • cegras
    • 3 weeks ago

    Great article!

    Reply
    • LiquidSquid
    • 3 weeks ago

    Thanks for the trip down memory lane. I have a few of these 13.8V supplies around (Car battery voltage for running HAM equipment and other car related crap)
    What is cool is a tiny SPS wall-wort for $10 can have more output power than one of these behemoths, and is much safer and far more power efficient. However, the SPS will also be far more noisy as far as electrical noise.

    Reply
      • ludi
      • 3 weeks ago

      Indeed, although the attractiveness of a bench supply is that the power switch and terminals are Right There for attaching whatever. The coworker I referenced in the video segment is squarely in the millennial generation and had somehow turned up one for hobby use, so that’s a pretty good sign that these things are as popular as ever among the DIY crowd.

      Reply
    • dragondaddybear
    • 3 weeks ago

    I love the dual post style. Also, I really love the humor.

    Reply
      • juzz86
      • 3 weeks ago

      Me too! Good job ludi, a great read mate!

      Reply
    • continuum
    • 3 weeks ago

    Slightly off-topic question, what’s with the grey text in parenthesis after the links? Is it some attempt at WCAG 2.0 compliance without proper tags in the CMS? Or some attempt at footnotes without actually doing footnotes? Just curious since I’ve never seen a site do that before…

    Reply
      • Ben Funk
      • 3 weeks ago

      It seems to be a way to differentiate a real link from an automatic one.

      Reply
        • ludi
        • 3 weeks ago

        Bingo. It also gives mobile users an easier way to determine if they want to visit the link, since mouse-hovering isn’t implemented as conveniently on a touchscreen.

        It may or may not be used [ever again / by any other authors / cheese ], but I thought I would try it out as an experiment.

        Reply
    • willmore
    • 3 weeks ago

    Before anyone says it again, at the voltages you’re going to find in low voltage sides of these boxes, the caps aren’t going to give you any shock at all. Now, in a modern switching mode power supply, the front end caps can have more than 2x peak AC voltage on them which is around 340V. That will gladly kill you.

    Reply
      • ludi
      • 3 weeks ago

      Yep. And as it happens, both designs in the article (and all three designs shown in the video feature) are constructed such that they bleed down pretty quick when shut down. Since neither I nor the TechReport could invest the proper resources to discuss all possible hazards illustrated in this review, we opted to cover it with multiple, plainly-worded, “don’t try this at home” disclaimers.

      Reply
    • willmore
    • 3 weeks ago

    Can you get some close up shots of the control board and pass transistor for the older power supply? We can probably pull some date codes off of there. Can you see what value the large resistor on the output is? It’s likely a shunt for overcurrent protection. I’d be the control board has an LM723 on it.

    Nice teardown–now on to the new design…

    Reply
    • DPete27
    • 3 weeks ago

    “See how I just nonchalantly fingered the solder terminals on the bottom of those larger capacitors without verifying that they’re discharged (or stating this step had been done prior)…don’t do that”

    I applaud the video content and i think it’s a strong start in the right direction. If I can offer any constructive criticism (no offense intended) it would be to spice up the delivery of the [admittedly dry] review content from the speaker. The effects were a welcome addition to keep things lively, but [IMO] the idea is to make this [boring] power converter sound like the coolest/funnest thing on the planet.
    Obviously most of us Millennial+ viewers are turned off by the LTT-style of delivery, but remember that Gen-Z is responsible for probably an order of magnitude more views and likes comparatively. I’d say that LTT generally doesn’t have the most in-depth or insightful content, but their STYLE of delivery is what attracts views in droves.
    I don’t have the answer whether to go full psycho on the video content in order to cater to the younger crowd while allowing the written content to continue drawing readership from the older generations, or if there’s a happy medium that can be struck.

    Reply
      • ludi
      • 3 weeks ago

      If that’s what you think people want, I’ll wait for you to make that video 🙂 It’s harder than it looks.

      Reply
        • DPete27
        • 3 weeks ago

        I absolutely agree.

        Reply
    • chuckula
    • 3 weeks ago

    Bonus safety tip since I see a nice big blue capacitor in there: Capacitors often hold substantial charge if you turn off the power supply without discharging them.

    So you need to watch out for a scenario where you run the power supply, fully disconnect it from the wall, and still have to worry about the potential for getting a nasty shock if you open it up to do work without making 100% sure the Capacitors are discharged

    Reply
      • dragondaddybear
      • 3 weeks ago

      When I was younger that was an evil trick I would do. I’d hand a charged cap (using a transformer and a battery to charge it) to someone and shock them. It was a take on the sock box I did in school. Very appropriate/fun/evil way to learn electron flow, basic circuits, and transformers.

      Reply
        • crabjokeman
        • 3 weeks ago

        We used to play “pass the capacitor” in lab, where we’d soft toss around an electrolytic capacitor and try to catch it by the cover to avoid getting shocked.

        Reply
    • chuckula
    • 3 weeks ago

    Sweet article and finally some subject matter on TR that can get you killed if you don’t do it right!

    Reply
      • Krogoth
      • 3 weeks ago

      “Our shilling can’t repel potential of this magnitude!”

      Reply
    • Krogoth
    • 3 weeks ago

    Unlimited Power!!!!!!

    Reply
    • redocbew
    • 3 weeks ago

    OMG WHO IS THIS WTF SO SAD

    Reply
    • usacomp2k3 (AJ)
    • 3 weeks ago

    Enjoying the read so far. Does Aaron have a forum handle that we recognize?

    Reply
    • In the video he clarifies that he’s ludi—as well as in the comments yesterday where he accidentally doxed himself, lol.

      Reply
        • ludi
        • 3 weeks ago

        Aaron? Never heard of him. *flips trenchcoat and scurries off*

        Reply
        • Can one of the mods ban this joker for running multiple accounts? 😉
          Seriously though, thanks for your work on this, it could be life-saving information and will directly impact my future purchasing decisions (in a good way).

          Reply
          • usacomp2k3 (AJ)
          • 3 weeks ago

          Great job sir! I really enjoyed the rest of the read. My dad’s dad was a big electrical hobbyist (worked for Ma Bell back in the day) and while the curiosity is genetic, the skill is not. It’s still somewhat black magic to see someone understand what’s going on.

          If you’re even in the Orlando area, you’d love Skycraft (https://www.skycraftsurplus.com/). They have all sorts of vintage electronics like old Agilent Oscilloscopes.

          Reply
            • ludi
            • 3 weeks ago

            Thanks!

            My dad is a lifetime electronics technician and also a hobbyist. I had the early advantage of learning a lot from him early in life, including proper soldering technique, and then went deep into DIY audio around 15 years ago. There are also a lot of good YouTubers that enjoy delving into electrical equipment, which is a great teaching shortcut that didn’t really exist 10+ years ago.

          • Mr Bill
          • 3 weeks ago

          Well written, useful, interesting, and humorous… [quote]We thought about doing so as a side-feature for this review but didn’t want to risk being stoned to death with Mountain Dew bottles.[/quote]
          You should write reviews more often.

          Reply
            • ludi
            • 3 weeks ago

            Sadly, I don’t tax my computer hardware as much as I used to, and that gives me less relevant material in which to geek out. The video editing and encoding for this review was the hardest I’ve worked my main desktop system in over a year, and my last from-scratch system build was a low-end Skylake HTPC nearly three years ago.

            If TR sticks around for a while and I find something interesting, I’d be open to doing it again.

          • Aether
          • 3 weeks ago

          Great lunchtime read; thanks!

          Reply
    • Captain Ned
    • 3 weeks ago

    The traditional “brand name” for inferior Chinese-sourced components is “Yum-Cha”.

    Reply
      • ludi
      • 3 weeks ago

      Interesting. I’ve been heavily into DIY electronics for a while and hadn’t heart that slang yet.

      Reply
        • ludi
        • 3 weeks ago

        *heard

        Reply
        • GhostofNappa
        • 3 weeks ago

        I’m not sure what this Yumcha is, but it sounds like a Raditz to me.

        Reply

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