Working with Mains Voltage: The Electrifying Conclusion!

This is the second in a two-part series looking at safety when experimenting with mains-voltage electronic equipment, including the voltages you might find derived from a mains supply but not extending to multi-kilovolt EHT except in passing. In the first part we looked at the safety aspects of your bench, protecting yourself from the mains supply, ensuring your tools and instruments are adequate for the voltages in hand, and finally with your mental approach to a piece of high-voltage equipment.

The mental part is the hard part, because that involves knowing a lot about the inner life of the mains-voltage design. So in this second article on mains voltages, we’ll look into where the higher voltages live inside consumer electronics.

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Looking Mains Voltage In The Eye And Surviving

It is often a surprise to see how other people react to mains electricity when they encounter it in a piece of equipment. As engineers who have dealt with it both personally and professionally for many years it is easy to forget that not everyone has had that experience. On one hand we wince at those who dive in with no fear of the consequences, on the other we are constantly surprised at the number of people who treat any item with more than a few volts in it as though it was contaminated with radioactive anthrax and are scared to even think about opening it up.

We recently had a chat among the Hackaday writers about how we could approach this subject. The easy way out is to be all Elf-and-Safety and join the radioactive anthrax crowd. But the conclusion we came to was that this site is a resource for hackers and makers. Some of you are going to lift the lid on boxes containing significant voltages no matter what, so we thought we’d help you do it safely rather than just listen for the distant screams.

So here follows the first in a series on how to approach electronic devices containing high voltages, and live to tell the tale. By “high voltages” we mean anything up to mains voltages, and those directly derived from them such as the few hundred volts rectified DC you’ll find in a switch-mode PSU. For multi-kilovolt EHT you’ll have to wait for another article, because that is an entire subject in itself. We’ll mention these higher voltages in passing, but their detail is best left for a Hackaday colleague with more pertinent experience.

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Colin Furze Gets Burned

Consider this a public service announcement. [Colin Furze], besides being a raging lunatic, seems to have the nine lives of a cat. Well, he’s not always so lucky, and now that we’ve recovered from being grossed out by the results, we’re glad that [Colin] posted this “fail” video.

Basically, he’s firing up one of his jet engines, and there’s a big fireball. He wasn’t wearing any protective clothing. This is hardly a spoiler — please don’t watch the video below if you’re grossed out by people visiting the doctor’s office to get their horrible second degree burns all up and down their forearm treated. You’ve probably learned the lesson already just by looking at the preview image.

Naturally, we’ve covered [Colin]’s videos before. He’s either very lucky or a little bit more careful than he lets on. We’ve seen him play with fire and not get burned, and stick a jet engine on a go-kart. We’re not gonna tell you what to do, but if that were us, we’d be wearing at least long sleeves and a helmet.

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New Research Sheds Light on 3D Printing Fumes

A few years back, there were some studies on the chemical and particle emissions coming out of the hotends of 3D printers. Although they galvanized a lot of people in the community, the science wasn’t entirely conclusive — one paper made it sound like you needed a hazmat suit for 3D printing, and the other suggested that cooking a meal in a kitchen was worse for you. That’s because they were measuring different things.

This new research paper on the emissions of 3D printers covers all the bases. They examined a variety of different materials printed in different printers. They also measured both chemical emissions and Ultrafine Particles (UFP) which can be hazardous even when the material itself is not.

We read the paper (PDF) so that you don’t have to. Here’s our takeaways:

  • 3d_printer_particles.pngThere was no significant variation across brands of 3D printers. (Duh?)
  • ABS and similar materials outgas styrene at levels you should probably be worrying about if you’re running your printer for a few hours a day in an unventilated office.
  • PLA emitted significantly less overall, and most of it was a non-hazardous chemical, lactide. PLA doesn’t look like a problem.
  • All of the materials resulted in increased UFP exposure. These levels are above normal household background levels, but lower than certain “microclimates” which (if you follow the references) include principals’ offices with carpet, automobiles, restaurants, and rooms with burning candles or running hair dryers. In short, the UFP exposure doesn’t look like it’s going to be a big deal unless you’re sitting right next to the printer and running it continually.

So what would we do? It now looks like it’s prudent to print ABS only in a well-ventilated room. Or enclose the printer in a box and vent whatever you can outside — which can also help prevent breezes cooling the piece down unevenly and adding to ABS’s warping problems. Or just stick to PLA. It looks essentially harmless.

Thanks [Jim Scheitel] for the tip!

Nanotech Makes Safer Lithium Batteries

Lithium-ion batteries typically contain two electrodes and an electrolyte. Shorting or overcharging the battery makes it generate heat. If the temperature reaches about 300 degrees Fahrenheit (150 degrees Celsius), the electrolyte can catch fire and explode.

spikesThere have been several attempts to make safer lithium-ion cells, but often these safety measures render them unusable after overheating. Stanford University researchers have a new method to protect from overheating cells that uses–what else–nanotechnology graphene. The trick is a thin film of polyethylene that contains tiny nickel spikes coated with graphene (see electron micrograph to the right).

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Powerful Crossbow is Almost Entirely 3D Printed

As it turns out, it’s not feasible to print an entire crossbow yet. But [Dan]’s crossbow build does a good job of leveraging what a 3D printer is good at. Most of the printed parts reside in the crossbow’s trigger group, and the diagrams in the write-up clearly show how the trigger, sear and safety all interact. Particularly nice is the automatic nature of the safety, which is engaged by drawing back the string. We also like the printed spring that keeps the quarrel in place on the bridle, and the Picatinny rail for mounting a scope. Non-printed parts include the aluminum tubes used in the stocks, and the bow itself, a composite design with fiberglass rods inside PVC pipe. The video below shows the crossbow in action, and it looks pretty powerful.

Actually, we’ll partially retract our earlier dismissal of entirely 3D-printed crossbows, but [Dan]’s version is a lot more practical and useful than this model. And for a more traditional crossbow design, check out this entirely hand-made crossbow.

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What Can Happen When You Do Try This At Home

In somewhat of a countdown format, [John McMaster] looked back over the last few years of projects and documented the incidents he’s suffered (and their causes) in the course of doing cool stuff.

[John] starts us off easy — mis-wiring and consequently blowing up a 400V power supply. He concludes “double-check wiring, especially with high power systems”. Other tips and hazards involve situations in which we seldom find ourselves: “always check CCTV” before entering the experiment chamber of a cyclotron to prevent getting irradiated. Sounds like good advice.

hotplate[John] also does a lot of IC decapping, which can involve both heat and nasty acids. His advice includes being ready for large spills with lots of baking soda on hand, and he points out the need to be much more careful with large batches of acid than with the usual smaller ones. Don’t store acid in unfamiliar bottles — all plastics aren’t created equal — and don’t store any of it in your bedroom.

The incidents are listed from least to most horrible, and second place goes to what was probably a dilute Hydrofluoric acid splash. Keyword: necrosis. First place is a DIY Hydrochloric acid fabrication that involves, naturally, combining pure hydrogen and chlorine gas. What could possibly go wrong?

Anyway, if you’re going to do “this” at home, and we know a bunch of you are: be careful, be protected, and be prepared.

Thanks [J. Peterson] for the tip!