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 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.
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.
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:
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.