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Medium sized Van de Graaff generÃ¡tor

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omegalabs

Fri May 02 2014, 04:30PM

Registered Member #1521 Joined: Thu Jun 05 2008, 10:46AM
Location: Hungary
Posts: 128

It's almost complete. A customer asked me to build a VDG to make classical physics demonstrations (especially hair lifting), so I decided I'll make about a 1m tall generator, with a 120mm acrylic tube. The motor is 24VDC, controlled by a simple 555 PWM circuit. The belt is from physicsplayground, I believe it's latex, 0,5mm thick. Top capacitor: stainless 300mm diameter sphere. And the most important things are the rollers, especially the materials. I thought a lot to decide which material can be used and where. I belive there is 2 methods to make the VDG work, one is to have the top and bottom rollers at the opposite end of the triboelectric series, and the belt is between them in the middle. The other one is to have one roller at one end of the triboeletric series, and the belt the opposite end, and the other roller should be metal.
So I made the bottom roller from polyoxymethilene, and the top is from teflon. Maybe poliurethane would be better instead of POM, but it works nice with this setup, so I'll try it next time with different roller materials.
It gives 35cm sparks, which hurts a lot. I can feel the electrostatic field from 1,5m, and it's a rainy day, so the humidity is probably very high. I'm going to test it when the humidity is lower, I think the output would be much better.

Video

HV Enthusiast

Fri May 02 2014, 07:59PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Very nice! VDGs are awesome!

Thanks for sharing!

omegalabs

Fri May 02 2014, 10:03PM

Registered Member #1521 Joined: Thu Jun 05 2008, 10:46AM
Location: Hungary
Posts: 128

Thanks!
I made another video of the sparks, it's hard to record it, because they're thin and short, unlike tesla coil sparks.
Video 2
These sparks stimulate my muscles in my arm, so it's not really comfortable to touch it.
I think I'm going to make a bigger version in the future.

I measured the charging current, it's 10uA at max RPM.

omegalabs

Mon May 05 2014, 06:51PM

Registered Member #1521 Joined: Thu Jun 05 2008, 10:46AM
Location: Hungary
Posts: 128

I made one picture of the sparks, with a high iso & exposure setting. In dark, the plasma is visible to the eye, looks really nice.

Mads Barnkob

Sun May 11 2014, 02:42PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Nice VDG.

Do you have any pictures of hair lifting?

I have had a large, 100cm diameter topload made for a VDG laying around for some years, got the tubing too, I think I will persue to build it when I am done with my large DRSSTC :)

omegalabs

Fri May 16 2014, 04:58AM

Registered Member #1521 Joined: Thu Jun 05 2008, 10:46AM
Location: Hungary
Posts: 128

Mads Barnkob wrote ...

Nice VDG.

Do you have any pictures of hair lifting?

I have had a large, 100cm diameter topload made for a VDG laying around for some years, got the tubing too, I think I will persue to build it when I am done with my large DRSSTC :)

No I don't know anyone with long hair unfortunately. 1m sphere? It would make bigger sparks than the drsstc

Mads Barnkob

Fri May 16 2014, 06:14AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

omegalabs wrote ...

No I don't know anyone with long hair unfortunately. 1m sphere? It would make bigger sparks than the drsstc

It is not a sphere, its half toroid on the bottom with the hole and the top of a sphere on top as a dome, if that makes sense :)

I am going to try with nylon and teflon roller and a rubber belt. Pretty thick, 1,5mm, as it was free. Perhaps add a 4kV source if its not fast enough, I still need to find a motor, what speeds do you normally run your motor at?

omegalabs

Fri May 16 2014, 05:08PM

Registered Member #1521 Joined: Thu Jun 05 2008, 10:46AM
Location: Hungary
Posts: 128

Mads Barnkob wrote ...

It is not a sphere, its half toroid on the bottom with the hole and the top of a sphere on top as a dome, if that makes sense :)

I am going to try with nylon and teflon roller and a rubber belt. Pretty thick, 1,5mm, as it was free. Perhaps add a 4kV source if its not fast enough, I still need to find a motor, what speeds do you normally run your motor at?

Yeah, I don't have a corona shield at the bottom of the sphere, but combined with a toroid it's even better than a single sphere.
Instead of nylon I suggest POM or polyurethane, these are way better for the roller material, however PU cost a lot more.
I had a hard time with the motor, I asked a few company here for a 24VDC 200W motor, and one of them had a price for 300euro. Then I decided to buy one of from ebay, mine is a roller motor: Motor
200W should be enough even for bigger VDGs. Their RPM is 2500 at max torque, and 3500 with no load. I made the drive to almost double this speed at max PWM setting, so the driver roller's RPM is a maximum about 5000 RPM. The roller diameter is 20mm.
Even at the lowest RPM setting it's charging to around 50kV, with max setting it produces almost 50cm sparks in every 4 sec if the humidity is low. And I think the 555 PWM is not really a good choice for motor control, it's not linear, and can't turn completely off. I won't change it on this one, but next time i'll use a small pic for this job.

1400260070 1521 FT162864 Triboelectric Polymer

omegalabs

Fri May 16 2014, 05:28PM

Registered Member #1521 Joined: Thu Jun 05 2008, 10:46AM
Location: Hungary
Posts: 128

I quickly welded a discharge wand, now I don't have to use my hand as a spark plug.
And a few long exposure photos too.

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob