Make Your Own Plasma Cutter

Of all the tools that exist, there aren’t many more futuristic than the plasma cutter, if a modern Star Wars cosplay if your idea of futuristic. That being said, plasma cutters are a powerful tool capable of making neat cuts through practically any material, and there are certainly worst ways to play with high voltage.

Lucky enough, [Plasanator] posted their tutorial for how to make a plasma cutter, showing the steps through which they gathered parts from “old microwaves, stoves, water heaters, air conditioners, car parts, and more” in the hopes of creating a low-budget plasma cutter better than any on YouTube or from a commercial vendor.

The plasma cutter does end up working up quite an arc, with the strength to slice through quarter-inch steel “like a hot knife through butter”.

Its parts list and schematic divide the systems into power control, high current DC, low voltage DC, and high voltage arc start:

  • The power control contains the step down transformer and contactor (allows the DC components to come on line)
  • The high current DC contains the bridge rectifier, large capacitors, and reed switch (used as a current sensor to allow the high voltage arc to fire right when the current starts to travel to the head, shutting down the high voltage arc system when it’s no longer necessary)
  • The low voltage DC contains the power switch, auto relays, 12V transformer, 120V terminal blocks, and a terminal strip
  • The high voltage arc start contains the microwave capacitor and a car ignition coil

At the cutting end, 13A is used to cut through quarter-inch steel. Considering the considerably high voltage cutter this is, a 20 A line breaker is needed for safety.

Once the project is in a more refined state, [Plasanator] plans on hiding components like the massive capacitors and transformer behind a metal or plastic enclosure, rather than have them exposed. This is mainly for safety reasons, although having the parts exposed is evocative of a steampunk aesthetic.

In several past designs, stove coils were used as current resistors and a Chevy control module as the high voltage arc start. The schematic may have become more refined with each build, but [Plasanator]’s desire to use whatever components were available certainly has not disappeared.

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Mini-VFD Clock Floats The Display Above It All

As [sjm4306] says, “You can never have too many clocks based on obsolete display technologies.” We couldn’t agree more, and this single-tube VFD clock is one we haven’t seen before.

The vacuum-fluorescent display that [sjm4306] chose to base this clock on is the IV-21, an eight-digit seven-segment display on the smallish side. The tube is Russian surplus from the ’80s, as all such displays seem to be. The main PCB sports an ATMega328, a boost converter to provide the high voltage needed to run the VFD, a real-time clock, and the driver chip for the tube segments. The tube itself lives on a clever riser card that elevates the display above the main PCB and puts it at the proper angle for reading. [sjm4306] designed it to be modular; should you want to user a bigger VFD you need only make a new riser PCB. Figuring out the proper way to space the through-holes in Eagle proved elusive, but he hacked a solution using a spreadsheet to handle the trigonometry and spit out Cartesian coordinates for each hole. Pretty neat. The video below shows the clock assembly and a test.

We really like the look of this clock for some reason – perhaps it’s the quirky nature of the VFD, or the soft teal glow of the digits. We’ve featured plenty of clocks with odd displays before: VFDs large and small, faux-NIMO, de-encapsulated LED “filaments”, and lots and lots of Nixies.

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Subaru Coils Make A Great HV Power Source

High-voltage experimenters are a unique breed. They’re particularly adept at scrounging for parts in all kinds of places, and identifying how to put all manner of components to use in the service of the almighty arc. [Jay] is one such inventor, and recently came across a useful device from Subaru.

The device in question is an ignition coil from the Subaru Outback. It consists of a pair of high-voltage transformers, connected together, in a wasted-spark setup to run four-cylinder engines. Having sourced the part from a friend, [Jay] realised that with some modification, it would make a great high-voltage power source. The first job was to figure out how to remove the internal electronics that drive the transformers. In this case, it was a simple job of hacking off a chunk of the case, removing the interfering hardware. With this done, it’s possible to directly access the transformer connections.

In [Jay]’s experiments, the device is run in an anti-parallel configuration, to produce higher than normal voltages at the output. In various tests, it’s demonstrated running from both a classic 555 circuit, as well as a ZVS driver. For future projects, [Jay] intends to use this setup to drive a large voltage multiplier, also noting it can be used with Tesla coils and plasma balls with the right additional hardware.

While [Jay] doesn’t include any specific model numbers, reports are that these coils are readily available in a variety of 1990s and 2000s Subaru vehicles. Others have used similar hardware to create high voltage projects, too – this stun gun is a great example. Video after the break.

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High Voltage Protects Low Denominations

How do you keep people out of your change jar? If you didn’t say with a 3D printed iris mechanism and high-voltage spark gap, then clearly you aren’t [Vije Miller]. Which is probably for the best, as we’re not sure we actually want to live in a world where there are two of these things.

Regular Hackaday readers will know that [Vije] has a way of using electromechanical trickery to inject a bit of excitement, and occasionally a little danger, into even the most mundane aspects of life. His latest project is an automated change jar that uses a pinpad to authenticate users, while everyone else gets the business end of a spark gap if the PIR sensor detects them getting to close.

You can see a demonstration of the jar in the video after the break, where he shows the jar’s ability to stop…himself, from getting access to it. Hey, nobody said it was meant to keep out real intruders. Though we do think a similar gadget could be a fun way to keep the kids out of the cookie jar before dinner, though we’d strongly suggest deleting the high-voltage component from the project before deploying it with a gullet full of Keebler’s best.

[Vije] was able to adapt a printable iris design he found on Thingiverse to fit over the mouth of the jar, and uses servos in the base to rotate the whole assembly around and open it up. The internal Arduino Nano handles reading from the pinpad, controlling the stepper, and of course firing up the spark generator for 1000 milliseconds each time the PIR sensor detects somebody trying to be cute. Just the sound of the arc should be enough to get somebody to reconsider the value of literal pocket change.

Some of the design elements used in this change jar’s high voltage components were influenced by the lessons learned when [Vije] was building his plasma-powered toilet air freshener. There’s a sentence we bet you never expected to read today.

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Hold 3500 Volts Up To Your Eye

Old military equipment can sometimes be found in places like flea markets and eBay for pennies, often because people don’t always know what they have. While [tsbrownie] knew exactly what he was getting when he ordered this mystery device, we’re not sure we could say the same thing if we stumbled upon it ourselves. What looks like a vacuum tube of some sort turns out to be an infrared sensor from an old submarine periscope that was repurposed as a night vision device. (Video, embedded below.)

Of course, getting a tube like this to work requires high voltage. This one specifically needs 3500V in order to work properly, but this was taken care of with a small circuit housed in a PVC-like enclosure. The enclosure houses the tube in the center, with an eye piece at one end and a camera lens at the other, attached presumably by a 3D-printed mount. The electronics are housed in the “grip” and the whole thing looks like a small sightglass with a handle. Once powered up, the device is able to show a classic green night vision scene.

Old analog equipment like this is pretty rare, as are people with the expertise to find these devices and get them working again in some capacity. This is a great video for anyone with an interest in tubes, old military gear, or even if you already built a more modern night vision system a while back.

Thanks to [Zzp100] for the tip!

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I Love The Smell Of ABS Plastic In The Morning

One lesson we can learn from the Vietnam War documentary Apocalypse Now is that only crazy people like terrible smells just for fun. Surely Lt. Col. Kilgore would appreciate the smell of 3D printers as well, but for those among us who are a little less insane, we might want a way to eliminate the weird (and not particularly healthy) smell of melting ABS plastic.

While a simple solution would be a large fume hood or a filter to prevent inhaling the fumes, there are more elegant solutions to this problem. [Mark]’s latest project uses an electrostatic precipitator (ESP) to remove the volatile plastic particles from the air. Essentially it is a wire with a strong voltage applied to it enclosed in a vessel of some sort. The voltage charges particles, which then travel to a collecting electrode. Commercial offerings also include an X-ray generator to help clean the air, but [Mark] found this to be prohibitively expensive.

The ESP is built into a small tube through with the air can flow, and the entire device itself is housed in the printing enclosure. The pictures show the corona discharge in the device, and [Mark] plans to test it over the next few months to determine its effectiveness. He does note, however, that the electrostatic discharge creates ozone, which has its own set of problems, so he recommends against building one on your own. Ozone at least still smells like victory.

A Lot Of Volts For Not A Lot

There was a time when high voltage in electronic devices was commonplace, and projects driving some form of vacuum or ionisation tube simply had to make use of a mains transformer from a handy tube radio or similar. In 2019 we don’t often have the need for more than a few volts, so when a Geiger–Müller tube needs a bit of juice, we’re stumped. [David Christensen] approached this problem by creating his own inverter, which can produce up to 1 kV from a 12 V supply.

Instead of opting for a flyback supply he’s taken a traditional step-up approach, winding his own transformer on a ferrite core. It has a centre-tapped primary which he drives in push-pull with a couple of MOSFETS, and on its secondary is a voltage multiplier chain. The MOSFETs take their drive at between 25 kHz and 50 kHz from a 555 timer circuit, and there is no feedback circuit.

It’s fair to say that this is a somewhat hair-raising circuit, particularly as he claims that it is capable of delivering that 1 kV at 20 W. It’s usual for high-voltage supplies driving very high impedance loads to incorporate a set of high-value resistors on their outputs to increase their internal impedance such that their danger is reduced. We’d thus exercise extreme care around this device, though we can see a lot of value in his description of the transformer winding.

We can’t criticise this circuit too much though, because some of us have been known to produce far hackier high voltage PSUs.