Static discharge using Lasers. - Page 1
Forum section: electronics / projects

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: June 26, 2015, 10:02:14 pm
content: A while ago I was taking temperature measurements of a fast moving paper web (paper rolls unwinding, going through an oven)was just using one of those cheap laser IR temperature probes. This web was heavily static charged.anyway I received a pretty decent static shock, and destroyed the sensor (i was around 2 meters away at the time). So I go off and buy a new ir probe and straight away same thing happened :wtfI cracked the sads after the second time and just made up the reading. It hurt too much and was getting expensive.Obviously laser light can conduct electricity ??It's got me thinking about making a static discharge device for industrial applications.Maybe an array of laser diodes shining through a fine steel mesh (Earthed) then onto a static affected surface.Has any one else come across this laser light phenomenon before? Any thoughts?Cheers

author: Ian.M
author_rank: Super Contributor
timestamp: June 26, 2015, 10:24:38 pm
content: Visible Laser light at power levels that do not cause atmospheric ionisation is just like ordinary light and does not make the atmosphere conductive. It can however, also like ordinary light, stimulate photoemission of electrons from surfaces, though this effect is usually insignificant at atmospheric pressure.To discharge charged surfaces, you'd need a high intensity short wavelength UV light source and unwanted ozone production would be a significant hazard.I suspect the IR probe would have suffered the same damage if you'd stood in the same place with it switched off . . . .

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: June 26, 2015, 10:32:18 pm
content: Quote from: Ian.M on June 26, 2015, 10:24:38 pmI received shocks both times as soon as the ir laser probe trigger was pulled. I was standing on a substantial steel walkway / bridge over the web at the time.

author: Kalvin
author_rank: Super Contributor
timestamp: June 27, 2015, 08:11:17 am
content: You have invented the basics for a laser printer.Anyway, I didn't imagine that the such a low power laser beam could create such a long conductive path in free air. Interesting, yet painful, discovery.High power lasers have been tested for triggering the lighting from the thunderclouds:https://en.wikipedia.org/wiki/Lightning#Artificially_triggeredI suggest you should not try to measure the temperature of the thunderclouds.

author: TerraHertz
author_rank: Super Contributor
timestamp: June 27, 2015, 08:56:32 am
content: Maybe you were lucky it was paper, not plastic film. Have a read of this:http://amasci.com/weird/unusual/e-wall.htmlThat was in the early 1990s. Were there IR laser thermometers then? Anyway, they didn't try that.

author: DanielS
author_rank: Frequent Contributor
timestamp: June 27, 2015, 01:00:38 pm
content: Quote from: B.B.Bubby on June 26, 2015, 10:32:18 pmYour IR thermometer has a plastic body. Your own body is insulated from the walkway by your shoes' rubber soles while the thermometer's internals are insulated by its plastic housing. Your body charges up to a different electrostatic potential than the thermometer's innards from ambient static charge and when you pull the trigger, your fingers get close enough to an internal conductive surface for a spark to jump and equalize the voltage, zapping whatever else it finds in its path.

author: LukeW
author_rank: Frequent Contributor
timestamp: June 27, 2015, 01:08:53 pm
content: For this sort of effect in a laser printer with infrared or visible light you need to have that light-sensitive semiconductor material on the drum, such as selenium.This sort of static discharge is sometimes done using a radioactive source to create ionisation (like those StaticMaster brushes, etc) but it's also possible using a short-wavelength ultraviolet light, eg. from a UV laser.If a plasma channel is opened in air with a UV laser, a whole lot of power can be dumped through it quickly.https://en.wikipedia.org/wiki/ElectrolaserBut the sort of phenomenon you're talking about probably can't happen, with most materials, with a visible or IR laser.

author: TerraHertz
author_rank: Super Contributor
timestamp: June 27, 2015, 02:34:56 pm
content: This is only very faintly related, but I just came across it now, and it's cool:google plasma wakefield accelerationWhere I read of it first:http://www.smbc-comics.com/index.php?id=3780

author: CatalinaWOW
author_rank: Super Contributor
timestamp: June 27, 2015, 05:12:34 pm
content: Quote from: DanielS on June 27, 2015, 01:00:38 pmI agree, with the addition that you probably consciously or unconsciously extended the sensor toward the point you were measuring as you triggered the reading. Most people seem to do this when using these probes. I am sure it is nothing to do with the laser beam. You could test that by just getting a cheap laser pointer with a conductive case (often sold in pet stores to amuse owners of cats and dogs) and pointing it at the paper rolls.

author: Siwastaja
author_rank: Super Contributor
timestamp: June 27, 2015, 05:44:06 pm
content: Quote from: Kalvin on June 27, 2015, 08:11:17 amNo, that's not how laser printer works.Indeed, the surface of the drum has a static charge, which is locally removed by using a laser.But the laser itself doesn't conduct; instead, the drum is coated with a light-sensitive material (traditionally, selenium; I don't know if they have come up with new materials) which starts to conduct when exposed to any light. The exposed parts conduct the static surface charge to the grounded drum itself. Before laser printers, traditional (analog) optical photocopiers simply projected the image to the drum by using a simple light source and lenses.OP could easily just turn off the laser pointer feature, these IR temperature probes do not work by lasers by any means, although people always make that assumption. The laser pointer is there just to make aiming easier, and can be turned off (or if not, covered by tape).

author: LaserSteve
author_rank: Super Contributor
timestamp: June 27, 2015, 10:18:20 pm
content: One, I've actually been in the room where the lasers pump a trial accelerator similar to what is in that linked cartoon.That said, get rid of the static by classical means. The pulsed laser you need for air breakdown over a tiny path costs 55,000$ and up just for the laser. That's not counting the means you need to have to sweep the beam back and forth etc. You cannot do it with a continuous wave laser, and it is hugely impractical to do it with a pulsed laser. Reason being is the practical laser can only zap a cubic millimeter at most at one time. If you have really specialized optics, you might ionize a two cm long thin thread at best. That's not going to help you clear a calendaring roll in a machine. Even if you scan the beam, you'd hit repetition rate issues with available lasers.Conductive materials, Antistatic Materials , changes in calendaring roller tribology, humidifiers, neutralized ion sources, pre-spaying an opposite charge, atmospheric pressure plasma machines etc ...ALL of them work far, far far, far, far better then a laser induced breakdown for this task.I do photonics for a living. One of my concerns used to be air breakdown on the faces of glass optics and non-linear crystals. I've sat and watched a tiny plasma ball form on my dead skin more then once. I know the mechanism quite well. This is not a cost effective means to use a nanosecond, picosecond, or femtosecond pulsed laser.This is state of the art, made using several graduate students, probably upwards of 100,000 USD worth of technology, and several man-years of work.https://youtu.be/AoWi10YVmfEIt clearly would not cover a high speed calendaring roll.Steve

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: June 27, 2015, 10:22:43 pm
content: Quote from: CatalinaWOW on June 27, 2015, 05:12:34 pmI'm certain the Laser did cause the discharge path. I did pretend to be Dirty harry whilst using it - but there was still a steel walkway between me and the web.I've done some thinking and googlingI don't think it was the actual paper web that was the source of the static discharge but more so its surrounding air.The paper is dried by large gas fired ovens and low pressure high volume air in a very very dusty environment.could have something to do with ionized air / dust and very low humidity?Anyway - I know a few teachers, may be able to borrow a Van De Graaf generator, if so ill try to replicate the conditions at home and do the experiment.Cheers

author: LaserSteve
author_rank: Super Contributor
timestamp: June 27, 2015, 10:37:59 pm
content: You wont see static reduction with any laser you can hold in your hand. Period.Steve

author: Kalvin
author_rank: Super Contributor
timestamp: June 28, 2015, 03:08:59 pm
content: This clearly calls for documented re-run of the experiment. Just set up a few video cameras (or cell phones with full hd or otherwise good quality video cameras) to film the test from different angles when firing the laser. After that, let's analyze.

author: Ian.M
author_rank: Super Contributor
timestamp: June 28, 2015, 03:14:24 pm
content: Video cameras in Faraday cages, otherwise the likely outcome is a big pile of dead electronics. Also, its likely to be highly dependent on ambient humidity, so time of day and weather conditions will be important for reproducibility.

author: LaserSteve
author_rank: Super Contributor
timestamp: June 28, 2015, 05:35:55 pm
content: And remember to run the test again and again, also with the laser in your hand but no beam emitted.Trust me, there is no way a 5 mW red or green laser aiming beam initiated a Townsend discharge or Leader Stroke in air to start a static discharge.Steve

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: June 28, 2015, 09:59:04 pm
content: Quote from: LaserSteve on June 28, 2015, 05:35:55 pmyeah but.... I still want to trywas thinking about setting something like this up.controlled room / chamberan earthed laser mounted in an earthed Faraday cage / remotely triggeredair con on to dehumidify the airportable gas stove on as a source of CO and any other combustion byproductsthe wifes hairdryer for some heat / maybe two of themvan de graaf generatorion discharge device (can maybe get an AC generator from work + 1M bar) would like DC + / - but we don't use them.A source of fine non explosive powder to float though the air ??A metal halide lamp mounted from the ceilingWould a neon globe in series with the lasers earth wire illuminate on a static discharge?Cheers

author: CatalinaWOW
author_rank: Super Contributor
timestamp: June 28, 2015, 11:35:12 pm
content: I'll have to temper my previous answer. It is often through something weird like this that "new physics" are discovered. So the experiment is welcome. Just recognize that if you find something, it will be totally unexplained by current models of how a 5 mW red laser interacts with air and charge.

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: June 28, 2015, 11:54:40 pm
content: Quote from: CatalinaWOW on June 28, 2015, 11:35:12 pmIf we are talking about triggering events that are chain reaction-ish, (https://en.wikipedia.org/wiki/Electron_avalanche) why does the power rating of the laser matter? isn't a photon a photon ie all photons of the same frequency have the same energy. It would only take one chance photon to trigger an event - just the chances are much less with a low power device?

author: LaserSteve
author_rank: Super Contributor
timestamp: June 29, 2015, 02:07:43 pm
content: The power level of the laser matters because it has to impart enough energy to overcome a high very threshold. It then has to create a long enough stream of electrons and ions to sustain a conductive path. This has to stay for a long enough time for the metal emitting the spark to achieve a very hot temperature in a very localized spot. Otherwise electrons will not "boil off" to sustain the discharge. Arcs need a huge amount of free electrons in a very short time. This calls for either Field Emission, which needs a sharp, nano-sized metal point to emit from, or a enough current for a red hot Cathode Spot to form.The Mean Free Path for a Red Photoelectron in air is less then 100 nanometers. It simply cannot bridge the distance.Nor could the 5 mW typical beam heat a localized spot of metal hot enough to initiate the arc emission. Certainly not in Air.The red light is also unlikely to overcome the "Work Function" required to liberate copious free electrons from any metal surface that would not oxidize immediately in air. Your not talking about a Sodium or Potassium photocathode material where red light could easily knock off a P or S orbital electron. Your talking about a iron or aluminum metal where the outer orbital shells are tightly bonded, mostly filled, and have very high bonding energy as they are far from the nucleus. So its safe to assume very few photoelectrons are liberated.If your aiming beam had any where near the legal maximum of 5 milliwatts for a class IIIA laser, that field would have been spread over a elliptical spot size of probably two millimeters in diameter. That fact, coupled with the fact that structural metals do not emit copious free electrons, ensured you never created a hot enough localized field to trigger an event. Period.Laser triggered spark gaps are used, but they require very high peak power, Q-Switched, Pulsed, lasers to trigger. They deliver the energy in about 7 nanoseconds, so the peak field strength is huge. You simply do not have the high peak field from a red pointer.I could do all the math to prove this, but I simply do not have the half day required to document the problem and look up the equations, constants, and materials properties.You observed a coincidence where you possibly squeezed the trigger right at the instant that a discharge was forming by other means.Steve

author: CatalinaWOW
author_rank: Super Contributor
timestamp: June 29, 2015, 05:05:03 pm
content: Quote from: LaserSteve on June 29, 2015, 02:07:43 pmWhen and if the experiment is duplicated, it will demonstrate that "something" is going on. All of the above correctly describes why it is highly unlikely to involve the laser. So, if the discharge can be repeatedly demonstrated you need to start doing things to isolate the true cause. Since the OP believes it is the laser the tests should start with things to sort that out. Simple things like moving the laser far away and coupling the beam to your test set up with mirrors. If the power of the beam is a concern in this test just add power at the input.Other obvious tests include turning the laser off and repeating.And if, after extensive attempts to prove that nothing else is going on, and various methods to prove that the laser is indeed the triggering event, WOOHOO, you will set off a flood of people trying to figure out what is going on. It might even prove to be important and lead to new technology applications, but even if real it is more likely to be a curiosity.

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: June 30, 2015, 07:25:12 am
content: Ok how about this as a theory as to what may have happened... ( doing google research, cause i'm obsessed with this)We have a surface that is statically charged.we have a gas region around this surface (boundary layer) - this gas is full of ionized air and byproducts of methane gas combustionalso in this gas are fumes from the ink drying process. Volatilized organic solvents. Precursors to organic semiconductorsOrganic semiconductors do shed electrons when exposed to low power visible light. + other weird stuff i do not understand.https://en.wikipedia.org/wiki/Organic_semiconductor#Charge_transport_in_disordered_organic_semiconductorsmaybe something like this is the air surrounding the ionized paper (released from the ink during drying)https://en.wikipedia.org/wiki/Anthracenealso see herehttps://en.wikipedia.org/wiki/PhotochemistryCheersSimon

author: LaserSteve
author_rank: Super Contributor
timestamp: June 30, 2015, 04:13:06 pm
content: If you have hot, ionized, air, that greatly lowers the threshold for the arc to span a given distance. Especially if it has combustion products in it. Flames conduct electricity very well, as there is a readily available supply of free ions. The laser light did not cause the threshold event. Something ELSE did, such as ignition of a thin streamer of Methane.Conversely if I have methane around, in flammable concentrations, I'm not going to be playing with high voltage, lasers, or other spark sources such as switch contacts arcing, even in low voltage circuits. Fuel Air explosions are amazingly powerful and dangerous. Not something you ever want to toy with in uncontrolled circumstances.Once you've seen a live FAE, you shudder at the thought of seeing another. They are highly efficient at creating energetic shockwaves.Steve

author: Ian.M
author_rank: Super Contributor
timestamp: June 30, 2015, 05:24:34 pm
content: There's also the paper dust issue. Without any methane or solvent vapours, is still a serious explosion hazard:https://en.wikipedia.org/wiki/Dust_explosionMaybe the answer is to install a large enough industrial humidifier to both cure the static problem and remove any risk of a dust explosion?

author: wiss
author_rank: Frequent Contributor
timestamp: June 30, 2015, 07:26:29 pm
content: How can IR-lasers be used to measure temperature?

author: LaserSteve
author_rank: Super Contributor
timestamp: June 30, 2015, 09:32:07 pm
content: Its not an IR laser in a common non-contact thermometer.A Pyroelectric detector is used to determine the temperature by looking at the 8 to 12 Micron wavelength FAR IR emission from the object being measured. With some mathematic corrections applied, its intensity is somewhat proportional to the object's temperature.A red aiming laser is used to show the user where the center of the instrument's field of view is located.Steve

author: wiss
author_rank: Frequent Contributor
timestamp: June 30, 2015, 10:23:51 pm
content: That's what I thoughtNo way this is related to the 5 mW diode laser.

author: Wim_L
author_rank: Regular Contributor
timestamp: July 01, 2015, 12:41:58 am
content: I agree such a small laser isn't likely to cause that.Do you notice significant airflow where you are standing? If that's ionised air, it could be charging insulators (such as the plastic parts of the thermometer).

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: July 01, 2015, 10:15:57 am
content: Quote from: Wim_L on July 01, 2015, 12:41:58 amThere could have been a sheltered area that allowed a big build up of ionized air - My memory fails me though.I'm not dismissing ideas like this, as on face value they are probably the most logicalIt's just that in all of my 20+ years working around industrial machinery that processes paper / plastic webs I've never had a random shock caused from static - except for when i took those two stupid temp measurements. I am sure the static discharge occurred the very moment the laser trigger was pulled.Anyway - why is some photo electric affect involving a low power laser (low power but still relatively high light intensity transmitted in a tube / conduit shape) so unbelievable ? We are not talking about shedding electrons from a metallic source, but rather shedding electrons from already heavily charged organic molecules or dust particles. I'm quite sure science backs this up. (i'm not a scientist's / physicist's arse hole, I just google stuff)I'll do the experiment. If i can repeat the results, cool, if not, meh.... I can only prove the effect exists not that it doesn'tI'll post a video either way.CheersSimon

author: LaserSteve
author_rank: Super Contributor
timestamp: July 01, 2015, 06:07:23 pm
content: Let me put it this way. The US Department of Defense, The Russian MOD, The UK MOD, Big Defense Contractors, Lots of Inventors, No doubt the Aussie MOD, and Evil Minions everywhere have put Hundreds of Millions of Dollars, Rubles, Pounds, Yuan, etc into attempting laser guided electrical discharges.None of them have ever published results using a CW laser of low power. If they could have, they would have, and we civilians would have known about it by now.Steve

author: Ian.M
author_rank: Super Contributor
timestamp: July 01, 2015, 07:32:04 pm
content: Which of course doesn't actually rule it out, it just makes it vanishingly unlikely, a bit like the odds of someone flying for the first time finding the only winning ticket to a British national lottery rollover on the floor of the Aukland airport transit lounge after their plane was diverted there due to an in-flight emergency. Long odds, stacked up many times in a row . . . .

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: July 01, 2015, 10:11:38 pm
content: Quote from: Ian.M on July 01, 2015, 07:32:04 pmYou can travel around the universe with that sort of logichttps://en.wikipedia.org/wiki/Technology_in_The_Hitchhiker's_Guide_to_the_Galaxy#Infinite_Improbability_Drive

author: schopi68
author_rank: Regular Contributor
timestamp: July 02, 2015, 07:38:40 am
content: What type of laser IR temperature probe has this been? Almost every one i know has an isolated plastic case, so this devices do not have a direct ground path or many isolating barriers between the laser-diode and earth.

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: July 02, 2015, 08:43:33 am
content: Quote from: schopi68 on July 02, 2015, 07:38:40 amYeah, just a mid range generic plastic unit.

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: July 02, 2015, 12:30:46 pm
content: Another laser phenomenon that may have been a contributing factor -http://www.chem.scphys.kyoto-u.ac.jp/nonnonWWW/watanabe/studies/photophoresis/index.html.enGetting motivated to start experimenting.Any one got a van de graff generator I can borrow?

author: Wim_L
author_rank: Regular Contributor
timestamp: July 02, 2015, 08:28:17 pm
content: Another thing to consider is this: if you were grounded on a metal walkway, and there is highly charged material passing nearby, you will have a strong field between you and that material. If you extend your arm towards the charged material to point the thermometer at it, you'd focus the field at your hand and can get some strong field gradients there.

author: abebarker
author_rank: Contributor
timestamp: July 02, 2015, 09:10:20 pm
content: I met a guy that said he and some class mates observed, pretty much, the same phenomena. I don't know how reliable of a source the guy is but I found the report interesting and have really wanted to test it.The guy said they had a Tesla coil in their class when they shone a laser pointer of 633nm next to it, the discharges would be conducted down the beam. They had other laser pointers of different wavelength but only the 633nm laser would work.Again, I don't know how credible the story is. I do find the idea intriguing though.

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: July 03, 2015, 09:29:31 am
content: Quote from: Wim_L on July 02, 2015, 08:28:17 pmYeah I can see how that would work, I've been over that walkway hundreds of times - but only twice did i reach over the railing with a thermometer gun in my hand doing really bad Danny Glover impersonations.

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: July 03, 2015, 09:30:36 am
content: Quote from: abebarker on July 02, 2015, 09:10:20 pmCan you remember any more about the conversation?

author: Ian.M
author_rank: Super Contributor
timestamp: July 03, 2015, 09:53:28 am
content: Running the numbers on the maximum possible surface power density in the laser spot, I get 1.59KW/sq m, which is only about 50% more than the power density of tropical noon desert sunlight. This makes the observed discharged vanishingly unlikely to be a electrooptical effect as unless its highly frequency sensitive or requires a coherent light source, such behaviour would be common knowledge, and a known design issue for above ground HV electrical distribution systems.

author: schopi68
author_rank: Regular Contributor
timestamp: July 03, 2015, 09:57:08 am
content: I am shure, if it would work to discharge static electricity via a laser beam, humans would no longer have trouble with thunderstorms.

author: Ian.M
author_rank: Super Contributor
timestamp: July 03, 2015, 10:16:06 am
content: Actually, you can (at least theoretically) trigger lightning 'on demand' by laser provided the correct type of charged culminonimbus cloud is overhead. See:http://iopscience.iop.org/1367-2630/4/1/361/fulltext/However they used a 50MW pulsed UV laser not a 5mW continuous visible red laser . . . .

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: July 03, 2015, 10:27:33 am
content: Quote from: Ian.M on July 03, 2015, 09:53:28 amExcept for some important differences...We are talking about a beam of light not randomly scattered wide area lighting (day light)a beam provides a conduit for the effect (if it does exist) ie: if particles can become trapped in this beam, they're all in a line and can interact and behave very differently than a mass amount of randomly scattered particles, it doesn't matter how bright that light is.. just the shape of this light.Could also have something to do with the monochromatic nature of the laser?There's at least one other bloke in the world who may have observed the effect...CheerSimon

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: July 03, 2015, 10:43:59 am
content: Quote from: Ian.M on July 03, 2015, 10:16:06 amDifferent things, I'm talking about a small 5mW laser being able to trap already ionized particles in its beam and use these particles as a discharge path. or the small laser is able to shed electrons from already heavily ionized air / dust / organic matter particles, this shedding could start an avalanche / chain reaction along the beams length, maybe instigated at millions of points simultaneously.Well that's what i think is happening -notthat a 5mW laser can ionize normal air to create the discharge - but if the atmospheric (charge) conditions are right, with the right sort of particles in it, than yeah maybe it can provide a discharge path, indoors, short range etc.

author: wiss
author_rank: Frequent Contributor
timestamp: July 03, 2015, 09:30:55 pm
content: Normal 5 mW lasers are less intense than sunlighy, after the the colimating lense.

author: TerraHertz
author_rank: Super Contributor
timestamp: July 04, 2015, 03:27:21 pm
content: Quote from: B.B.Bubby on July 02, 2015, 12:30:46 pmNo, but I do have a 0 to 200KV regulated power supply. SouthWest Sydney area.I've been trying to get around to setting up the Faraday cage it needs around it (to be safe to use in my small workshop) so I can try some experiments related to something else (that LED sparkle ball thing from another thread.) The cage will be soon; I'm not doing anything fancy, probably just chicken wire (ha ha very appropriate.)What occurred to me to try, related to your laser scenario, is to put two sphere electrodes spaced JUST far enough to not ark over in air. One of them with a small hole through it, so a laser can be shone between the two at closest distance. So, a relatively short distance, like 6 inches to a foot will do for the experiment. 200KV - can do.The idea being if the air gap is only just not quite arcing, then any tendency of the laser at all to initiate an arc actually will. If it does, the spheres can be moved apart till nothing happens. That will show what degree of effect the laser has.Only guessing about mechanism, but if it does work I think it will be due to the laser stimulating photoelectric emission from the surface, (in the high E field). Excess ions near a point on the surface will accelerate in the field, and form a leader cascade 'point', concentrating the field more as the leader point extends. Possibly with the laser beam assisting further ionization at the point, since there there's a zone where the air is reaching breakdown point anyway, and any extra energy (the photons) will kick it over. So there'll be a kind of guiding effect. The laser couldn't do it by itself, but it can steer the much greater energy available in the electrostatic field.I'd guess it will only work in E field gradients not far below arc-over levels.Your moving film/paper might build up charge to just below arc-over level, but self-limit there due to volume corona effects draining the charge before it gets to breakdown at any point. Until someone shines a laser at it...

author: abebarker
author_rank: Contributor
timestamp: July 04, 2015, 05:07:50 pm
content: Quote from: B.B.Bubby on July 03, 2015, 09:30:36 amThere isn't much more to tell. He said they would shine the laser across the room onto a wall. The Tesla coil was closer to the wall than it was to them. The discharges from the coil would travel down the laser beam toward the wall. He was adamant that the discharges would only travel down the 633nm laser beam and not the beam of other wavelengths.I believe he said he went to school in Tooele Utah (pronounced TOO-WILL-AH). He said that he was a Cobra pilot in Desert Storm but that is irrelevant.

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: July 05, 2015, 10:50:40 am
content: Quote from: TerraHertz on July 04, 2015, 03:27:21 pm0-200kV power supplyI'm half way through building a 40cm van de graaffHopefully I can start trying out a few things in the next few days.

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: July 05, 2015, 11:02:53 am
content: Quote from: abebarker on July 04, 2015, 05:07:50 pmThanks mate, weird how they didn't follow up on it.

author: TerraHertz
author_rank: Super Contributor
timestamp: July 05, 2015, 11:29:53 am
content: Quote from: B.B.Bubby on July 05, 2015, 10:50:40 amPity about those flanges on your top ball... uh, two bowls. Those will corona discharge away and cut your top achievable voltage down a lot.Where are you? If Sydney, I have a few spare metal donuts if you want one.Last year I found a tossed out exercise treadmill. The track is about six foot long, big rubber belt with motor drive, rollers, etc.I grabbed it thinking wow, possible huge Van de Graph generator. But I haven't come up with anything insulating (I can find for free) to replace the steel side frames. Needs to be solid. Big fat fiberglass bars, or something like that. Wood is not suitable. PVC piping not strong enough. Though, now I come to think of it, *large* PVC pipe would probably work.Hmm. Also I could slit the belt and use a narrow width. That would fit inside a large tube. Also it would give me spare belts.

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: July 05, 2015, 11:44:45 am
content: Quote from: TerraHertz on July 05, 2015, 11:29:53 amThanks for offer, I'm in Melbourne.so you be looking for a globe about this size for the tread mill beltI'll try taping the lips, if that's not enough i'll go hardcore with an angle grinder -- and some aluminium tape to join themIf all else fails, its off to IKEA for some lip less salad bowls (google is awesome - they seem pretty popular for home made VDG';s)

author: TerraHertz
author_rank: Super Contributor
timestamp: July 09, 2015, 01:32:19 am
content: Quote from: B.B.Bubby on July 05, 2015, 11:44:45 amHeh, taping the lips, with what?Save yourself some time learning about very surprising insulating material punch-through, (or trying to make clean angle grinder cuts on thin curved metal) and go get the rimless salad bowls. Or, leave it as it is till your VanDeGraph is running, then you can swap the sphere later and see what a difference it makes.Some interesting reading:http://4hv.org/news.phpHigh voltage forumhttp://www.coultersmithing.com/Similar, but with a fusion focus.

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: July 09, 2015, 05:09:15 am
content: Took your advice - two bowls from ikea for $23but the steel's too thick for my tin snipsSo now I need an $89, 100mm hole saw from bunningsscrew you buddy!

author: B.B.Bubby
author_rank: Regular Contributor
timestamp: July 11, 2015, 09:13:44 am
content: Just in case anyone else ever wants to build a van de graaff generator, pretty much all the Triboelectric charts on the net are crap!!!!however, this one is good -https://www.trifield.com/content/tribo-electric-series/Bloody internet regurgitators!

author: TerraHertz
author_rank: Super Contributor
timestamp: July 12, 2015, 02:06:26 am
content: Quote from: B.B.Bubby on July 09, 2015, 05:09:15 amHeh. The travails of trying to build stuff with improvised parts. Story of my life.But you don't need the hole saw. A compass to scribe a circle, a small drill (lots of holes along the line) and a file will do the job. Just take a bit longer. Or for the lazy, a small round grinding stone bit with a drill.Large dia. hole saw won't work on thin metal anyway. The center hole edges won't have enough strength to hold the outer hole saw centered. Unless you use backing sheet of wood or something. Have fun clamping the bowl to it.Edit:Wait, why are you concerned with surface friction charge transfer for a VanDeGraph?You don't need to be. At the lower belt roller you transfer charge to the belt surface with a corona discharge, using a HV DC supply like from a photocopier, and a line of corona points or thin wire. Ground the metal roller, have the corona points outside and close to the belt. You can make this supply + or -.Due to the high local field strength at the points, lots of charge transfer, and it gets stuck on the non-conductive belt.Up inside the top shell, there's no E field since it's a Faraday cage. A conductive brush or roller allows the charge to escape from the belt surface, to the shell. The whole point of a VanDeGraph is to mechanically carry the charge on the belt, up through the main E field (which wants the charge to go the other way.)How you get the charge on the belt at the bottom, and off the belt inside the top shell, isn't important and can be done various different ways.Pretty much any insulating material will do for the belt. I've seen plans for a VanDeGraph built using pumped oil in plastic tubing as the charge carrier - an idea I'd like to try someday, but probably won't.