How a Van de Graaff Generator Works

[@RimstarOrg]

Thanks! I'm glad you liked it. It was a lot of work so your feedback is appreciated. -Steve

[@rogueart7706]

Excellent video! You are the only person on KZbin who actually explains this. Thanks a bunch!!

[@6123ish]

Absolutely agree with you. I have watched many videos about this topic, no one can explain how the positive charges accumulate on the outer surface of the belt, but he did.

[@josephjoe9525]

Finally, a person who explains this in detail! I don't get why other youtubers explain the Van de Graaff generator as a machine that simply collects electrons and they leave at that explanation, which is vague and does not really makes sense.

[@RimstarOrg]

You're welcome. And thanks for you generous feedback. I'm kind of fond of this one myself but it's reassuring to hear it from others.

[@ajanki34]

I have to agree with everyone - your explanation of how the charges move and where they're coming form and going to is perfect. This video needs to be made into a section in a physics or an electrical engineering text book, seriously. Thank you for laying it out. Your video is in my play list. I'm going to make a Van De Graaff generator too.

[@mrbhave]

If you're not an educator by trade, you have certainly earned this educator's respect. Very well done.

[@RimstarOrg]

Thanks. That's a big complement indeed. I spent 13 years traveling around the world teaching for a software company, I currently teach a few times a year for an adult education program, and have done other teaching and course development over the years. I can't seem to stop myself. :)

[@mrbhave]

It's an insidious passion of mine, too, friend. Learn something new everyday, I say. It keeps Alzheimer's and boredom at bay.

[@RimstarOrg]

I'm glad my presentation helps! Thanks for letting me know.

[@Carlos2312]

Just discovered you channel. I'm a fourth semester electric engineering student from Venezuela and this is just breathtaking for me. Thank you for the videos!

[@betatester03]

Wow, this was so much more informative than I expected from a KZbin video. Excellent video!

[@RimstarOrg]

Thanks. It's a lot of fun (but also a huge amount of work) making these detailed ones. Two others which I'm proud of are How a Crystal Radio Works kzbin.info/www/bejne/Zl6zgZSoiNKqqqc and How a Wimshurst Machine Works kzbin.info/www/bejne/pHKXknaaatZ5jdU

[@learnerrahat5320]

@@RimstarOrg you didnt leave a single little question. every small details was explained. nce work. thanks.

[@sdilarasenel]

To understand Van de Graff Generator, I watched a lot of videos and this one was the most informative and useful one for me. Thank you for your effort! :)👏

[@felixmeyer1972]

Das ist eine gute "How to"-Anleitung. Interessant war die Verwendung von Isolierband für den Antriebsriemen und wie man es auf die Rollen legt. Danke für die Zeit und Mühe, diese Videos zu machen. Es hilft vielen Menschen und inspiriert sie, etwas aufzubauen.

[@davef5208]

You explain it much better than Plasma Channel

[@RimstarOrg]

Wow! You're welcome! I'm delighted you liked it so much. And thanks for saying so.

[@FANBASEALPHA2]

This is just simply an excellent description. A comprehensive class unto itself. The best on the internet. Thanks for your efforts.

[@RimstarOrg]

Yes, by sharper surface I mean smaller in diameter. Assuming 79kv between two domes, the smallest diameter dome has the stronger electric field around it. The air molecules will be repelled from the smaller diameter one, and be attracted to the larger diameter one. And you're welcome. Glad I can help.

[@RimstarOrg]

You're welcome. I'm glad you like the videos. Thanks for watching them!

[@RimstarOrg]

I'm glad you liked it, thanks. And welcome to interacting on KZbin.

[@RimstarOrg]

I'm glad to hear it. I try to leave nothing to the imagination so maybe that's why my explanation works for you. Thanks for the feedback.

[@bsshabssha]

Great Great Great. Thanks. First time in my life to understand clear easy I try many channels at you youtube but you are the best

[@RimstarOrg]

That's a perfectly reasonable question. A big use for them in the past was for generating high voltages, in the millions of volts, for particle accelerators for doing science experiments. I don't know if any particle accelerators still use them. These days they're mostly used in classrooms for teaching about electrostatics or by hobbyists who just like to play around with high voltages. Science museums also use them for demonstrating electrostatic phenomenon.

[@RimstarOrg]

Thanks! And thanks for the feedback. It's good to know the explanation works.

[@RimstarOrg]

Yes, the effect only charges the inner side of the belt. But the main reason is that the charge on the inner side of the belt is spread out over the larger inner area of the belt. The roller, however, has a smaller surface area and so the charge is more compact, the voltage is higher. So we use that higher voltage to pull more charge onto the outer surface of the belt. As a result, the outer surface of the belt has more charge than the inner surface. It's that larger charge that we're after.

[@imanultrastarwarrior801]

I gotta say you really did well on explaining this device, and even the effects that happen on the machine

[@reverseengineering1931]

Best video to clarify all doubts about Faraday cage etc.

[@RimstarOrg]

Thanks. The section explaining how the Faraday cage works is a little contentious since I wasn't using the standard approach to explaining it with just fields. But I really wanted to do it at the electron and proton level; more tangible, and also consistent with the rest of it. Have fun making your Van de Graaff generator. Be sure and check out my videos on that topic and ask questions if you run into problems.

[@deepshabad]

This is the best video I have seen for some one who wants to understand the Van De Graaff generator. Thanks Rimstar.

[@RimstarOrg]

You're welcome. Thanks for the feedback.

[@RimstarOrg]

Yes. Air contains a number of different atoms. One I know for sure gets ionized negatively is oxygen, which can then attach to an O2 molecule to produce ozone (O3). I'm don't know offhand which ones get positively charged. I talked about atoms becoming ionized in the video but molecules (which are made up of multiple atoms) can also become charged.

[@RimstarOrg]

Thanks. I tried to make it as complete as I could for the popular types of Van de Graaffs at least.

[@RimstarOrg]

Not usually. The electric field and resulting current flow are usually too weak. However, you can sometimes replace the regular multimeter probes with a high voltage probe to measure weak electric fields - by contact with the affected surfaces. You can see one of these probes in action in yet another of my videos :) "High Voltage Probe How-to with Fluke 80K-40".

[@RimstarOrg]

Yes, you can use the same materials with a small homemade van de graaff. In fact the small one I show at 2:12 in this video has a Teflon roller at the bottom and a metal roller at the top and uses a rubber band for the belt. Using metal for the top roller is less effective than using something that's triboelectrically positive with respect to the belt material but the teflon and rubber band combination works so well that the results are still very good.

[@nguyenthanhat3547]

my bad at english and your good at presentation make my mind blow :)) ho ho ho thank you. Such a good guy. Spend a lot of his time to help people :D

[@pedropalhari7849]

even though I do not know English, the video is so didactic that I understood, thank you very much!!! from Brazil, translated by google translate hehehe

[@Kr3sk1n]

I searched hours for this explanation.. THANK YOU

[@RimstarOrg]

Thanks. I'm glad it helped. Yeah. as long as the connection is to the inside of the dome then you're okay. Connecting to the outside makes it much less efficient.

[@RimstarOrg]

(... continued) The same for a capacitor. The more charge you put on the cap plates, the stronger the electric field between the plates, the higher the voltage. The VDG dome and ground can be considered a capacitor. Pressure is sometimes useful analogy for voltage. By pumping more charge onto the dome you've built up the pressure. Bring a grounded ball close to the dome and the charge on the dome rearranges closer to the ball. The pressure may increase until the charge bursts across the gap.

[@RimstarOrg]

Voltage is measured between 2 things. Example, my big VDG is rated at 500kV with respect to Earth ground since the lower brush is wired to Earth ground. To measure the voltage, use a HV probe. Connect the HV end of the probe to the dome and the other end to ground. The probe will feel the effect of the electric field between the dome and ground. The electric field strength is determined by the amount of charge. Picture one field line between each dome charge and a ground charge. (continued...)

[@RimstarOrg]

The upper brush is connected to the inside of the dome. Is that what you thought, or did the video somehow lead you to think it was connected to the inside? If so, which part of the video made you think that?

[@RimstarOrg]

The charge is deposited using the triboelectric effect. When two particular materials make contact and then break contact, their molecules interact such that charge is exchanged while they are touching but doesn't get restore when the separate. The belt and rollers are constantly making and breaking contact. And yes, we are transporting the protons and electrons exactly like transporting materials on a simple conveyor belt. See my video Triboelectric video, see link in this video's description.

[@RimstarOrg]

The charge would accumulate on their surfaces with most of it on the areas that face each other. As more and more charge accumulates, the electric field between them would become stronger and the air would start to ionize until finally it becomes conductive and an arc would occur between them. At that point the domes would no longer be charged and the whole process would start over again.

[@RimstarOrg]

The motor has a power chord which is plugged into the wall socket to power the motor. That power chord has three wires: a black wire, a white wire, and a green wire called GROUND. That green ground wire goes through the wall socket and eventually to a metal rod in the ground in the backyard. That green ground wire is the one you see in the video at 2:04. The brush and the green ground wire are both connected to the metal case so they are connected together. Let me know if that doesn't help.

[@taquenos]

Thank you for the video, it's the best explanation I found on Van Der Graaf generator, now I can build my own knowing how it works and why.

[@egr8735]

Thanks! During the last days I have been trying to make my own generator without success. Your video helps me a lot to see why my attempt didn't work. Now I *finally* understand why there is some charge accumulation at all (ie, which is the origin of the first charge gradient).

[@RimstarOrg]

Glad to hear it helps! Know how it works makes all the difference between engineering and guesswork. Let us know how it goes.

[@RimstarOrg]

You're welcome. I hope my answers helped. Cheers.

[@RimstarOrg]

Sorry, I don't know of a good website off-hand. I used my old high school physics textbook to double-check my knowledge of this. My approach was to first make sure my understanding of the relationship between electric fields and voltages was right. They're proportional to each other, denser e-field = higher voltage. Then I reminded myself that a charged VDG dome is a capacitor, with the room being the other plate. Since voltages are the same, e-field is the same, affect on ions is the same.

[@RimstarOrg]

Actually, the photoelectric effect may happen with the positive brush (the bottom one) but I'm not sure that it does. With the negative brush (the top one) the electrons near the brush spread outward more and so the photoelectric effect plays a bigger part in contributing electrons to the corona.

[@ishitasagar8909]

The triboelectric effect's video really helped.. Thanks a lot for helping and clearing my doubts :)

[@poojakulkarni9175]

its the best video on van de graaff generator..thanks for uploading it

[@RimstarOrg]

You're right hat rubber is an insulator but that just means it's a poor conductor of electricity. It doesn't mean you can't deposit or take electrons away from it and that's what's going on when the rubber makes and breaks contact with the rollers. Then, instead of the charge conducting along the belt from one roller to the other roller, we move the belt. By physically moving the belt from one roller to the other we physically move the static charge too.

[@RimstarOrg]

If you have an ice pail with a large enough opening, you could put the terminal of an electroscope inside and the electroscope leafs wouldn't repel each other. If you're not familiar with electroscopes, see my video "How to make an electroscope (DIY)" (to help you find is it's one of my oldest videos.)

[@RimstarOrg]

Off-hand I don't know. The faster it turns, the more charge you'll pump, so as high a gear ratio as you can do is the most I can suggest. It does depend on a number of things, probably the main one being how wide the contact area is where your belt contacts your roller, since that's where the charges are separated. The wider that is the slower you can turn and get a decent amount of charge.

[@sipos66]

Very informative. I wondered how they worked. I just wanted to see how the dome was constructed and attached to the circuit. Thanks.

[@RimstarOrg]

You can use a cylinder as long as one end is closed. So one end is open for the top part of the Van de Graaff and the opposite end is closed. Make sure to avoid having sharp edges though, as they'll decrease the output.

[@RimstarOrg]

Both of my VDGs in this video were bought, I didn't make them from scratch. The big one was from amazing1 dot com. They don't sell the domes separately. A lot of people make the domes by attaching two steel salad bowls together at their open ends and cutting a hole in the bottom of one. After you make the cut, smooth out the edge; sharp edges reduce the voltage. Note that VDGs produce high voltage but not a lot of energy; the current is very small.

[@JamHir01]

It's my first time to log-in my account to KZbin. To like and comment to your video. Very informative, thank you very much! :)

[@WhakyD]

Going to have to watch this many times. Very detailed. Thanks!

[@RimstarOrg]

Funny. You asked the same question in the comment to my How to Make a Van de Graaff Generator video. I replied there (the answer was yes, and I suggested you watch this video which I guess you didn't since the answer's in it :)).

[@ecrouch77]

Could you use a negative ion generator to enhance the demonstration?

[@RimstarOrg]

Definitely not a stupid question. I wonder this myself. The only answer I can come up with is that most easy to do ways of making physical contact with the belt will wear down the belt over time. I've done this by having my ground wire touching a rubber belt. The wire scraped away the belt surface; there was rubber powder all over.

[@RimstarOrg]

I don't have a video on that. Though if you look at my "How to make an electroscope" video it's the same thing that makes the leafs inside the jar spread apart. If the VDG dome is positively charged then the hair is also positively charged and since like charges repel each other, the hairs all repel, getting as far apart as they can. Similarly if the VDG is negative then the hair is negative and repels.

[@RimstarOrg]

Charge leaks more easily to the surrounding air from sharp edges. Charges bunch up more at sharp edges creating a strong electric field which interacts strongly with the surrounding air. See 5:18 in the video. Now a large dome, by definition has a very smooth surface, no sharp edges. The larger it is the less round it is at any point. So you get less charge bunching up and weaker electric field. The charge stays on the dome instead of leaking to the air. That means a higher voltage. continued...

[@cynthiasathees9220]

your video is amazing it really helped to understand what a van de graaf genarator is

[@RimstarOrg]

You're welcome! I'm sure the little ones will be delighted. Have fun!

[@darkcnotion]

Best explanation and the questions give better insight, thanks

[@RimstarOrg]

The voltage is limited by the size of the dome. Try to go higher and the charge just leaks off. So a larger dome would increase voltage.

[@daddy7973]

Super great explain. I was not knowing earlier, I am not knowing now how it works. There are thousands of conflicts in my mind.

[@RimstarOrg]

Thanks. I'm glad to hear it helped.

[@pomme4682]

The short explanation is that charge is sprayed onto the moving belt due to the action of the lower points. This charge is then carried up into the hollow metal dome. Faraday's ice pail experiment shows there can be no charge inside a hollow conductor so the charges migrate to the outside of the dome. The potential builds up until the air breaks down in a spark discharge . The energy for all this comes from the work done against the repulsive forces as the belt moves upwards.

[@RimstarOrg]

It should work if you connect the brush to the INSIDE of the leydon jar, not the outer cylinder. It has to use the faraday ice pail effect. Avoid sharp edges on inside cylinder of the leyden jar if you can.

[@RimstarOrg]

By the way, which Myles? There seem to be two of them depending on if you include user in the URL.

[@RimstarOrg]

@lx0199 I purchased the generator years ago as a whole from Information Unlimited (I'll put the link to their website in the video description.) The unit itself is made by Science First (again, link in the description or just search for their name) and was a slightly different positive charge version of their # 615-3145. I don't see any spare rollers for sale on either of their websites, though Science First does sell the belts. Contact them to find out what the belt is made of.

[@MrJamaal11]

amazing. your better than my physics teacher who went to oxford!!!

[@RimstarOrg]

Oh good. I wasn't sure I'd understood your question correctly. Thanks for letting me know.

[@RimstarOrg]

...continued. If you compare the two domes at 14:58 in the video you'll see the one on the left has a "sharper" surface than the one on the right. The one on the left can reach only 80kV because at that point the electric field around the dome is so strong that any more charge just leaks to the air. The one on the right is supposed to be able to reach 500kV before any additional charge leaks to the air. Let me know if that didn't clear it up.

[@RimstarOrg]

If you connected the battery to the outside of the sphere you wouldn't get any additional result. The sphere would just be at the voltage of whichever battery terminal you connected it to. Even if you connect it to the inside, the battery would need a circuit to conduct.

[@RimstarOrg]

Oh, interesting idea, twisting the belt! I'm not sure if the Van de Graaff dome would still charge up but it might accumulate more on the rollers. Hmmm. Regarding no external power source, it wouldn't. You need an external power source and you can't accumulate energy more than you use.

[@RimstarOrg]

I'd love to do a video explaining how a tesla coils works. I looked around and saw the same thing you did. However, I don't have the same level of background with tesla coils as I do with Van de Graaff generators. For a tesla coil that would mean building a few different tesla coils, which I'd like to do but haven't had time yet. It's on my todo list but it'll take a while.

[@RimstarOrg]

@JeanAlex23 Glad to hear it, thanks.

[@RimstarOrg]

Oh good, glad to hear it helped. Thanks.

[@catherinefei6629]

Such a nice video to study for Physics Exam!! Thank you!

[@RimstarOrg]

I've never looked for teflon material so I don't know how costly it is. I usually just use a plastic of some kind. It won't be dangerous. The voltage is high but the current is very small.

[@RimstarOrg]

@daytonharmon94 Thanks, and you're welcome. I do the best I can.

[@RimstarOrg]

There are different ways to explain things, and at different level. My explanation was as a very low level. Maybe they're really both right. What was different in his explanation?

[@rohanjaiswal8582]

how does the inner surface of the belt become negatively charged rather than being neutral while returning to the lower roller?

[@RimstarOrg]

Good point. The positive charges on the inner surface of the belt on the way up would attract at most and equal negative charge from the roller but not more. So on the way down the inner surface of the belt would either be less positive than it was on the way up or it would be neutral.

[@HoorGuvLabs]

Man's replaying to comments 10 years later

[@h7opolo]

12 years later, too.

[@RimstarOrg]

You're welcome. I'm glad I could help.

[@daytonharmon94]

Wow this is an amazing video. I love learning things like this thank you so much for helping me understand better

[@bobthetiger11]

AMAZING!!!!! BEST EXPLANATION I HAVE SEEN!!!! THANKS SO MUCH!!

[@RimstarOrg]

I don't understand it fully enough at that level to say for sure but I think it's atomic. When the materials come together, chemical bonds form between atoms in some areas. When the materials are pulled apart, some atoms have a tendency to keep shared electrons and some have a tendency to give them away.

[@drbobhacker1803]

Awesome work! Now I understand it! Too bad this was not around when I was a college student.

[@IAmKoach]

this is brilliant! I learned a lot from this video. can I make a request? can you make a video explaining how a tesla coil works? the other videos about the tesla coil doesnt a good explanation or is plain boring.

[@debistutisaha4170]

Minute attention to every small steps of the generator and detailed description of its working... Really makes worth watching the...Really made the things so much easy and interesting...

[@RimstarOrg]

If they're both at the same voltage then the effect on ions in the air would be the same. To have a voltage they must have a voltage with respect to something. Let's say the domes are at 79kV w.r.t. the room. Having the same voltage means the electric field lines are equally dense around both. Since one dome has a larger surface area, it must have more charge for there to be the same number of e-field lines as the smaller dome. With the same e-field density, the effect on ions is the same.

[@Jeplans]

Great stuff, I always enjoy your videos.

[@MrElapid]

You gave a great explanation thanks for putting this up! Was horrified at some of the comments below the primary grades K-12 sure aren't what they used to be. Having fun printing conductive PLA and making little induction machines and also just finished a VDG using a printed sphere. Awesome retirement fun as I can now make conductors in most any shape within reason. Did a 200mm. sphere with the bottom curving gently up to the top end of the tube, looks a little like a torus from the bottom. Or a sphere that somebody sat on. Results v. good. Sounds like you're having fun with this me too it's interesting stuff.

[@dhanunjaynaidu2900]

It's great explanation 👍

[@tiarne_i_think7537]

Thanks so much! This has helped my physics revision improve SO WELL x

[@RimstarOrg]

Thanks! That's high praise; that's a good school.

[@RimstarOrg]

@sanches2 Thanks! My pleasure.

[@yellow6ird]

Awesome awesome video, thank you so much! Answered a lot of my questions I couldn't gets my heads around!