In high voltage applications involving tens of thousands of volts, too often people think about the high voltage needed but don’t consider the current. This is especially so when part of the circuit that the charge travels through is an air gap, and the charge is in the form of ions. That’s a far cry from electrons flowing in copper wire or moving through resistors.
Consider the lifter. The lifter is a fun, lightweight flying machine. It consists of a thin wire and an aluminum foil skirt separated by an air gap. Apply 25kV volts across that air gap and it lifts into the air.
Lifter flying with high voltage power supply
So you’d think that the small handheld Van de Graaff generator pictured below, that’s capable of 80kV, could power the lifter. However, like many high voltage applications, the lifter works by ionizing air, in this case ionizing air surrounding the thin wire resulting in a bluish corona. That sets off a chain of events that produces a downward flowing jet of air, commonly called ion wind, lifting the lifter upward.
Having hacked away with high voltage for many years I’ve ended up using a large number of very different high voltage sources. I say sources and not power supplies because I’ve even powered a corona motor by rubbing a PVC pipe with a cotton cloth, making use of the triboelectric effect. But while the voltage from that is high, the current is too low for producing the necessary ion wind to make a lifter fly up off a tabletop. For that I use a flyback transformer and Cockcroft-Walton voltage multiplier power supply that’s plugged into a wall socket.
So yes, I have an unorthodox skillset when it comes to sourcing high voltage. It’s time I sat down and listed most of the power sources I’ve used over the years, including a bit about how they work, what their output is like and what they can be used for, as well as some idea of cost or ease of making. The order is from least powerful to most powerful so keep reading for the ones that really bite.
You’ve no doubt encountered this effect. It’s how your body is charged when you rub your feet on carpet and then get a shock from touching a door knob. When you rub two specific materials together there’s a transfer of electrons from one to the other. Not just any two materials will work. To find out which materials are good to use, have a look at a triboelectric series table.
Materials that are on the positive end of the table will become positively charged when rubbed against materials on the negative end of the table. Those materials will become negatively charged. The further apart they are in the table, the stronger the charging.
Electrospinning is a fascinating process where a high voltage potential is applied between a conductive emitter nozzle and a collector screen. A polymer solution is then slowly dispensed from the nozzle. The repulsion of negative charges in the solution forces fine fibers emanate from the liquid. Those fibers are then rapidly accelerated towards the collector screen by the electric field while being stretched and thinned down to a few hundred nanometers in diameter. The large surface area of the fine fibers lets them dry during their flight towards the collector screen, where they build up to a fine, fabric-like material. We’ve noticed that electrospinning is hoped to enable fully automated manufacturing of wearable textiles in the future.
[Douglas Miller] already has experience cooking up small batches of microscopic fibers. He’s already made carbon nanotubes in his microwave. The next step is turning those nanotubes into materials and fabrics in alow-cost, open source electrospinning machine, his entry for the Hackaday Prize.
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.
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.
High voltage is not something we usually tinker with at home. In fact, most of us are more comfortable working with non-lethal, low current, low voltage DC signals. When we do venture into the world of high voltage, we prefer to do it vicariously thru someone with more safety training and/or experience.
[Mike] shows us the inner workings of a 240VAC circuit breaker and explains how the different safety features in the device work. In proper MikesElectricStuff form, [Mike] finds out what it takes to destroy the device. Or in this case multiple devices, [Mike] uses his “Destruct-o-tron” to create catastrophic failure in more than one breaker. You can check out the video embedded after the break to learn a bit about how a circuit breaker works, and of course witness the carnage.