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June 11, 2003

New sign, posted today at Tor
Posted by Teresa at 04:46 PM *

We’ve been good.

We deserve a
Van de Graaf Generator.

And a Tesla Coil.

Comments on New sign, posted today at Tor:
#1 ::: Teresa Nielsen Hayden ::: (view all by) ::: June 11, 2003, 04:48 PM:

It's to go with the Tor Zeppelin, which we keep moored at the top of the Flatiron Building.

Claire Eddy wants a theremin for the conference room.

#2 ::: Holly M. ::: (view all by) ::: June 11, 2003, 05:26 PM:

Are these to help generate bright ideas?

(sorry)

#3 ::: Xopher ::: (view all by) ::: June 11, 2003, 05:34 PM:

You can get a theremin for just over $400 here.

#4 ::: Xopher ::: (view all by) ::: June 11, 2003, 05:35 PM:

Oh, drat. My attempt at putting in a link didn't work. It was to http://www.moogmusic.com/cgi-local/SoftCart.100.exe/products_t.html?L+scstore+gxyr6642ff749974+1055697409

#5 ::: Xopher ::: (view all by) ::: June 11, 2003, 05:36 PM:

(Also, I have one if you just want to play. I'm sure Patrick could play it; I can't even make a scale come out.)

#6 ::: Cassandra ::: (view all by) ::: June 11, 2003, 06:28 PM:

You can get a virtual desktop theremin from the BBC website.

#7 ::: Kip W ::: (view all by) ::: June 11, 2003, 06:39 PM:

A friend of mine built one from a kit. Unfortunately, the volume modulator doesn't modulate. Back to the old drawing board.

#8 ::: Stefan Jones ::: (view all by) ::: June 11, 2003, 07:06 PM:

I bet the money you'll save thanks to the tax cuts will be enough to let you buy a Tesla Coil!

Um, well, OK, maybe enough to buy some rubber-soled shoes suitable for rubbing on the carpet to generate really killer static shocks.

#9 ::: Mary Kay ::: (view all by) ::: June 11, 2003, 07:31 PM:

Erik Olson was telling me just last night in AIM that he had just built a Van de Graaf generator and was thinking about juicing it up. Maybe you should talk to him.

MKK

#10 ::: Jordin Kare ::: (view all by) ::: June 11, 2003, 10:47 PM:

I've always been fond of Wimshurst machines, myself, but I'll admit I've never thought of getting one as a reward for good behavior.

I will note, however, that if you can only have one, Van de Graaf generators pretty much have to have spherical high voltage terminals (since the top of the belt is inside the sphere) but Tesla coils are generally topped with... Toroids!

#11 ::: Erik V. Olson ::: (view all by) ::: June 11, 2003, 11:10 PM:

Jordin. You put the toroid *vertical* on the Van de Graaf. :)

Seriously. Homebrew Telsa coils are a bunch of work -- work that goes up exponetially with power. 0.01uF capacitors are cheap -- but ones that can handle 10KV aren't, 100KV are even worse -- making them is much cheaper, this involves lots of folding foil and polyethyene, and oil. Not Fun. Winding the secondary is a pain, you really need a variac to control it, and if you screw up, you die.

Desktop Tesla Coils are easier -- American Science and Surplus will sell you a lovely 50KV one for about $150, IIRC.

Wimshurst machines are way, way cool, as are dirods, but you need to be very ept with machining to build larger ones. Still, with hooking up to leyden jars, they're the fastest ways to get big bolts. WARNING. If you do not understand just how dangerous adding leyden jars is, you are in no way safe doing so. Serious. Capacitance and High Voltage are *DEADLY* if you screw up.

I'm rather fond of GT -- at a given convention now, we'll have Jeff's 400KV Tesla, Dave Johnson's 20" Wimshurst (about 200KV) and my VDG, also about 200KV right now, but we're working on that....

For Homebrew Fun, the VDG is the way to go. Only two fiddly mechanical bits -- the rollers and hooking the motor to it. 95% of the parts can be found at Home Depot & K Mart -- the only part you really need to search for is the motor. Ideally, you'll find a lovely sphere (like I just found), but you can get quite nice sparks with two mixing bowls taped together -- you'll get corona with the rims, which will limit your voltage. Belts? Latex, look for those "exercise bands" that they sell as low resistance workouts. Rollers? Lots of ideas. I built mine from bearing, steel rod, nylon spacers (for the top roller, making my VDG generate positive.) and PVC for the lower -- teflon would be better, but PVS is trivial to find. Easier? skateboard wheels, put a PVC sleeve on one of them. Will Erik build another one, with the PVC at the top, and the nylon on the base, just to have a negative VDG to match the positive one? Could be....

Right now, with the motor now 1-2 belted, not direct, I'm getting 150uA, at about 200KV, and tons of corona off the bowls. I love the smell of Ozone in the morning. As soon as I get the hole cut and peened in the sphere, I think I'll be able to store about 350 -- and new bearings in the top roller means I should be able to run a 1-3 gearing -- putting the top roller at about 5000rpm, current over 200uA. Whee! I briefly hooked up my Foredom motor, at 15,000 rpm, for about 30 seconds, it was amazing. Then the main belt broke. Oops.

I'm considering grabbing a ionizer rig from Goldmine Electronics -- a lovely 7.5KV DC source, complete with brush. Charging with a DC source is much more reliable than counting on the triboelectric series, but has hazards. Still, DC charging is how the really big VDGs and Pelletrons work.

#12 ::: Lois Fundis ::: (view all by) ::: June 12, 2003, 01:29 AM:

Crossing threads: How about a theremin for your kitchen? It might not cook the food but it would give you something to play with while it's in the oven.

Erik seems to be having a similar idea with the Van de Graaf generator: "you can get quite nice sparks with two mixing bowls taped together".

(You can get quite nice sparks by putting a fork in the microwave, too, of course, but this is Not Recommended.)

#13 ::: Paula Lieberman ::: (view all by) ::: June 12, 2003, 02:42 AM:

One of my college professors described being stuck inside a Van de Graaf generator when someone who didn't realize that there was someone up in the ball. It didn't hurt him, but....

=============

It's been a long time since I was an college undergraduate doing undergraduate research at the Magnet Lab. One of the professors there got known as the only person in the world who could weld concrete -- somethng about a resistor buried in the concrete floor, and arcing Bitter plates on Alcator 1, with some number of kilovolts at kiloamperage on it. ZAP!!! Then there there was Versator and the banks of thyristors or whatever hooked up to an impressive array of large capacitors.... the only lab accident fatality I remember hearing about on campus while I was there was a grad student from India who had the lack of sense to be standing in a a puddle of water when working with live high voltage on terminals of a high power laser or some such in the basement of building 4 or 2 or 6.

#14 ::: Ray Radlein ::: (view all by) ::: June 12, 2003, 06:17 AM:

It occurs to me, without looking around to verify, that this quote must originally taken the form of a series of tiny signs held up by Nicole Hollander's cats. Am I right?

#15 ::: Erik V. Olson ::: (view all by) ::: June 12, 2003, 11:48 AM:

The deeply cool VDG at the Museum of Science in Boston -- largest air-insulated in the world, cranking out 2.5MV at huge (for VDG) currents -- use to be two seperate terminals, charged opposite, allowing a potential of 5MV. The bolts would fire at a target between them, and were monitored from the lab stations. Where were the lab stations?

Inside the spheres. With HV, you get the skin effect -- the charge is repelling itself (like charges repel) and tries to get as far away as possible. As far away on a sphere is the outside of the sphere. This is the same principal that makes the VDG work, makes Faraday Cages safe, and makes your car a safe place during a thunderstorm -- provided you have a steel body, not fiberglass. You can even touch the inside of the cage/sphere, at full charge, with no risk. Demonstrators at the MoS do this -- and most of them have let thier fingers slip through the bars, to the outside of the cage. Ouch!

To get real voltages, you have to beat two problems -- charge migration on the belt, and corona breakdown in the atmosphere. National Electrostactics Inc. makes research machines, under the brand name Pellotron. They use nylon chains with conductive strips, rather than belts (the chains can be drive much harder and faster, as well) and they immerse the whole thing in something with a higher breakdown voltage than air. At first, pressurized air, now they use various things like Sodium Hexofluoride. These machines can generate, oh, 25MV, at near 1A. Don't play with these. Spinning the belt doesn't really raise the voltage (Voltage is limited by how much you can store on the terminal) but does raise the current, and I've seen Pellotrons that are moving 6" wide chains at 30K RPM -- through a liquid. Fierce beasts, but one of the more effective ways to get very high voltage DC.

#16 ::: Erik V. Olson ::: (view all by) ::: June 12, 2003, 11:49 AM:

+5 points for Ray. Exactly right.

#17 ::: Teresa Nielsen Hayden ::: (view all by) ::: June 12, 2003, 12:52 PM:

Huh. You're right. It does sound like Nicole Hollander, though it's actually me.

Yesterday at work was one of those days that's like scuffing your brain on the carpet over and over, until by late afternoon you have sparks popping out of it. That's when I put up the sign. It's separated into three parts to leave room for torque.

#18 ::: Tim Kyger ::: (view all by) ::: June 12, 2003, 01:22 PM:

What you *really* need is a Jacob's Ladder.

"It's *ALIVE!* Bwa ha ha ha!!!"

#19 ::: Erik V. Olson ::: (view all by) ::: June 12, 2003, 01:36 PM:

Jacob's ladders are easy -- Neon sign transformer, coat hanger. But! Jacob's ladders are also very, very dangerous. Think of them as bug-zappers, optimized for 6 year old kids.

#20 ::: Claude Muncey ::: (view all by) ::: June 12, 2003, 01:42 PM:

Many years ago, in a galaxy far, far away . . .

Well, at Merced High in 1972 . . .

We had a brand new physics teacher that year, and one of the projects we had was building as big a Tesla coil as we could, and drive a really nice spark gap. No, I don't remember how big or powerful (which might be a side effect of the coil -- hmmm . . .) but I do remember the lovely things it did to the florescent lights one night, and (I swear) the quiet inquiry we got from the local Air Force base. It seems that the electronics warfare officers on the B-52's coming in on approach over the school could pick up the rig when it was running and just wondered . . .

#21 ::: lightning ::: (view all by) ::: June 12, 2003, 04:35 PM:

Tesla coils are only difficult if you try to get fancy. Neon sign transformer, spark gap (two quarter inch bolts in a fuse clip), capacitor (glass, aluminum foil, tape), primary coil, secondary coil. The secondary coil is the only really hard part -- we used a lathe at very low speed and a lot of magnet wire. Biggest problem is insulating the secondary, so your discharges are at the end instead of along the coil.

Side effect is that radio and broadcast TV stop working anywhere near you when you turn it on.

Have I mentioned how much fun my high school electronics class was?

#22 ::: Erik V. Olson ::: (view all by) ::: June 12, 2003, 04:40 PM:

Tesla coils, being very high frequency (100KHz is not uncommon) AC sources (Well, HF compared to wall current), drive fluorencent tubes quite nicely -- Neon, Argon and Krypton tubes are fun. So do plasma globes, which also have high frequency AC, do as well. Be careful, though, not to touch *metal* to the globes -- you can quickly get a nasty RF burn.

Telsa coils are pulsed -- they build a charge in very large capacitors (not a lot of capactiance, mind you, but stunning breakthrough voltage) and fire that off. The problem is that there aren't many switches that can handle that kind of power, and cycle fast enough. The easiest to build is a spark gap -- when the voltage reaches a certain point, it arcs over.

Spark gaps were also the very first radio transmitters. As transmitters, they're illegal -- they "transmit" over a vast frequency, saturating it with noise. I'm not surprised an EW airplane noticed a running coil -- electromagnetically, it's shouting "HERE I AM" in a loud voice.

VDG's aren't as fun with tubes, since there DC, but they do flash nicely.

#23 ::: Claude Muncey ::: (view all by) ::: June 12, 2003, 05:31 PM:

Especially, Eric, as 52's were concerned not only with the more conventional pulsed microwave radar, but with some of the older Soviet low band CW systems that weren't very precise, but could work over longer distances (forward scatter), as well as Soviet countermeasures. A good spark gap looked like a fairly crude jammer . . . because it was.

The interesting part was that because there are multiple EW antenna sets and the BUFF is big, they were easily able to figure out where we were.

#24 ::: Bill Higgins ::: (view all by) ::: June 12, 2003, 07:25 PM:

Erik, I had no idea you were building a VdG. Should have spent more time talking to you last weekend.

Not long ago I moved to a new office on the second floor of the Linac gallery at Fermilab. Directly underneath me is a big metal room holding a 750,000-volt Cockroft-Walton accelerator-- a cousin of the Van de Graaf. (Uses a voltage-multiplier circuit, rather than a moving rubber belt, to attain high voltages.) Within its dome is a little bottle of hydrogen, where our protons start their journey.

Every so often, something goes wrong and it sparks. Usually two or three times. It's like hearing gunshots go off downstairs. One gets used to it.

#25 ::: Erik V. Olson ::: (view all by) ::: June 12, 2003, 07:53 PM:

Erik, I had no idea you were building a VdG.

Sigh. The Mark I version was in the GT suite...

#26 ::: Jordin Kare ::: (view all by) ::: June 12, 2003, 10:41 PM:

Erik: National Electrostactics Inc. makes research machines, under the brand name Pellotron. ... These machines can generate, oh, 25MV, at near 1A.

That seems a bit excessive, since that would be near 25 MW of electric power. Do they really have a 40,000 horsepower motor driving a Pellotron? 25 MV at 1 mA I'd believe...

Also, you mention sulfur hexafluoride insulation, which for no obvious reason makes me want to come up with a molecular group named "whatthe", just so I could synthesized whatthe hexafluoride.

#27 ::: Bill Higgins ::: (view all by) ::: June 12, 2003, 10:45 PM:

Oh. That was *your* machine?

It was late. I was tired. I'd done too much programming.

Frankly, I didn't think of you as the kind of techie who builds such a thing. Which is, of course, an excellent reason to do so. Gotta keep 'em guessing.

It was fun to watch you playing with it. When are you bringing it to the Flatiron Building?

#28 ::: Scott Lynch ::: (view all by) ::: June 13, 2003, 03:01 AM:

My junior high school science teacher, the immortal Bob Schumacher, had a handbuilt Tesla Coil that he used to cause full-scale evacuations of the building twice during my eight-grade year (the fire alarm system was, in his words, "a real oversensitive sissy").

The previous year, he had been a high school science teacher. His demonstration of the principles of combustion involved a two-liter container of what he claimed was "hair gel," a fifty-foot waterproof wick, and the stately pond in front of the high school. This device threw a twenty-foot geyser of water into the air (and sent every fish in the pond to Icthyoid Heaven) just as the Assistant District Superintendant and the Principal came out of the front of the building on their way to lunch.

The next year, he was teaching at the junior high. Coincidence? I don't know. Bob's benevolent disregard for the unwritten laws of civilized Tesla Coil use sure made him a tough act to follow, though.

#29 ::: James D. Macdonald ::: (view all by) ::: June 13, 2003, 08:47 AM:

Here's workshop instructions on building a Van de Graf generator from a tin can.

#30 ::: Bruce Arthurs ::: (view all by) ::: June 13, 2003, 09:47 AM:

I guess this is the difference between working for a science fiction publisher and working for the Postal Service. If a sign like that went up at my substation, it would probably ask for strippers and a couple of kegs.

#31 ::: Erik V. Olson ::: (view all by) ::: June 13, 2003, 12:29 PM:

That seems a bit excessive, since that would be near 25 MW of electric power. Do they really have a 40,000 horsepower motor driving a Pellotron? 25 MV at 1 mA I'd believe...

I swear, there was a m in that there...

Here's a huge pelletron, 25MV, housed in a 100' tall pressure vessle, filled with SF6 at ~70 PSIG. Theye. They mention that a spark firing from this beast has an energy of 200KJ, implying a steady state current in the range of 1mA. They work very hard to keep that beast from arcing.

#32 ::: Kip W ::: (view all by) ::: June 13, 2003, 07:42 PM:

Someone needs to do an analysis of whether it's cheaper to have a Van de Graaf generator, or simply to take advantage of the present supply of Van de Graafs.

Also, I think Tesla shuffled off the coil some time ago, alas. My old electronics teacher was convinced that Mr. Tesla had made a device the size of a pack of cigarettes that you could keep in your shirt pocket that would generate a force field which would keep anybody from touching you.

The same teacher also used to regale us with tales of a lake, way up in Canada, surrounded by chain link fence and security. This lake would periodically emit a circular energy disk that would rise up and eventually go into space. If a plane got in its way, it would simply push the plane aside.

I liked him. He told some good stories.

#33 ::: LauraJMixon ::: (view all by) ::: June 17, 2003, 10:59 PM:

You also need a toroidal (sorry, I couldn't help myself) fusion generator.

#34 ::: clew ::: (view all by) ::: June 19, 2003, 04:50 PM:

I must recommend the Instrument Room at the Teyler Museum in Haarlem.

The instruments are, startlingly often, those built by or for the people they're named for - Wheatstone's own bridge, etc. They're even more beautiful than they need to be, because they were demonstration instruments when that was a fashionable entertainment.

There's a modest little case with sections from the whole phylogeny of undersea cables.

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