The Van De Graff generator is a device capable of generating potentially millions of volts of electricity which you can build in an afternoon, probably from parts you’ve got in the junk bin. This is not a fact that’s escaped the notice of hackers for decades, and accordingly we’ve seen several Van De Graaff builds over the years. So has high voltage hacker [Jay Bowles], but he still thought he could bring something new to the table.
Put simply, a Van De Graaff generator creates static electricity from the friction of two metal combs rubbing against a moving belt, which is known as the triboelectric effect. The belt is stretched between the two combs and passes through an insulated tube, which serves to “pump” electrons from one side to the other. The end result is that a massive charge builds up on the positive side of the Van De Graaff generator, which is all too willing to send a spark firing off towards whatever negatively charged object gets close enough.
The video after the break guides viewers through the process of turning this principle into a practical device, illustrating how remarkably simple it really is. A common hobby motor is used to get the belt going, in this case just a wide rubber band, and the rest of the components are easily sourced or fabricated. Even for what’s arguably the most intricate element of the build, the combs themselves, [Jay] uses nothing more exotic than aluminum foil tape and a piece of stranded wire splayed out.
Combined with the acrylic base and the purpose-made metal sphere (rather than using a soda can or other upcycled object), the final result not only generates healthy sparks but looks good doing it. Though if the final fit and finish isn’t important, you could always build one out of stuff you found in the trash.
We tend to think of electricity as part of the modern world. However, Thales of Mietus recorded information about static electricity around 585 BC. This Greek philosopher found that rubbing amber with fur would cause the amber to attract lightweight objects like feathers. Interestingly enough, a few hundred years later, the aeolipile — a crude steam engine sometimes called Hero’s engine — appeared. If the ancients had put the two ideas together, they could have invented the topic of this post: electrostatic generators. As far as we know, they didn’t.
It would be 1663 before Otto von Guericke experimented with a sulfur globe rubbed by hand. This led to Isaac Newton suggesting glass globes and a host of other improvements from other contributors ranging from a woolen pad to a collector electrode. By 1746, William Watson had a machine consisting of multiple glass globes, a sword, and a gun barrel. Continue reading “Hair-Raising Tales of Electrostatic Generators”→
What I particularly like about the Van de Graaff (or VDG) is that it’s a combination of a few discrete scientific principles and some mechanically produced current, making it an interesting study. For example, did you know that its voltage is limited mostly by the diameter and curvature of the dome? That’s why a handheld one is harmless but you want to avoid getting zapped by one with a 15″ diameter dome. What follows is a journey through the workings of this interesting high voltage generator.
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.
Good news from CadSoft this week. They didn’t miss all the complaints about their decision to use a Node Lock License for EAGLE 7. This had meant that users of the popular PCB design software would be limit on how many machines they could use the software with a license. They have removed License Management from the package (and all the citizens rejoiced).
We’re tripping over the growing pile of hardware that boast the “next-big-thing” in getting devices onto a network. That’s not a complaint at all. This time around it’s a cell chip, the U-blox SARA-U260, which can connect to 3G on the AT&T network and is just 16x26mm. They call it world’s smallest but we have no idea if that’s true or not. Anyone have a source and/or pricing for these? [Thanks Austin]
This guy loves his Nixie tube. How much? To the extent that he built up a hardware and software interface that behaves much like a pet. It’s voice activated, and the infectious delight of [Glasslinger’s] video demo is in itself worth watching. [Thanks Morris]
We know from watching Breaking Bad that you can kill power to a building by shorting the power lines outside with a huge bouquet of mylar balloons. This installation is a twist on the idea. Connecting one mylar balloon to a Van de Graaff generator and floating it next to another results in an oscillating repel-discharge-repel cycle. [Thanks filnt via NPR]
This Van de Graaf generator was built using mostly parts on hand. The only thing that was purchased for the project was the Christmas ornament shaped M&M candy tin that serves as the collecting sphere. We didn’t include the in-action shot in the banner because it’s so dark. But sure enough, this will generate the visible sparks that make the device famous.
The gist of the device is that it uses rotating belt to generate static electricity. This potential is stored in the metal collecting sphere on top until a path for discharge is provided. They’re an awful lot of fun in middle-school science class as long hair can be made to stand on end if you touch one while your body is insulated from ground. This build uses a long rubber band as the belt. The band is moved by the motor from a DVD drive tray which is housed in the PVC base. An empty prescription pill bottle bridges the gap between the base and the metal sphere.