Help with Van De Graaff Generator Build

[pianomanjcb]

Greetings,

I am building my own van de graaff generator and have run into a problem: No charge.

My bottom roller is a PLA-3D Printed spool wrapped with many layers of Teflon Plumbers Tape.
My top roller is a Borosilicate Glass Tube I bought off Amazon (https://www.amazon.com/gp/product/B07YZ69Y4Q/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1)

My belt is tan natural rubber I bought off McMaster Carr (https://www.mcmaster.com/6856k11)

I thought these materials would work well, but does anyone see why these materials wouldn't play well together?

Pictures of my van de graaff generator are here: https://drive.google.com/drive/folders/1Do202KY-32-uGZIv8u-y8K7p_Y3Rfrl3?usp=sharing

There will eventually be a dome on top, but right now I don't have that installed. There was still zero charge build up at the top.

Your help is appreciated.

[johnf]

What electron spray are you using onto the belt??
what do the charge and discharge combs look like??

How fast is your belt moving??
: note ideal speed is 70km/H ie 40 MPH

[pianomanjcb]

John,

I am using metal wire cup brushes for both combs: https://www.amazon.com/gp/product/B001GM1HAI/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

My belt is powered by an electric scooter motor... it's not slow, but it's definitely not going 40MPH. I will test my assembly with a faster motor and see if that produces different results.

As far as electron spray goes, I have no active design for that. The teflon becoming negatively charged and drawing positive charges from the comb onto the rubber belt was the plan.

Thank you,
Jordan

[haversin]

Nice build. Several things come to mind.

1) I couldn't tell in your photos if the lower brush has a ground connection. If it doesn't have one it needs one.

2) Teflon tape does not charge like pure Teflon. In tests I've done Teflon tape charges positive against PVC pipe (pure Teflon should charge negative) and charges negative against latex rubber. Triboelectric tests are notorious for being very sensitive to surface conditions, however I've done this test several times and always got the same result.

3) Glass is prone to charge leakage. You might try cleaning the glass upper roller with rubbing alcohol and drying with a hair dryer.  You also might try using a hair dryer on the VDG belt and column. I've had to do this to get a VDG working after I cleaned the belt with soap and water.

4) The upper brush has so many corona points that it may be difficult to tell if it's charging. This will not be an issue with the enclosing top dome because of the Faraday ice pale effect. If you have meter, trying attaching it between the upper and lower brushes to see if you have any DC current in the uA range. The old rule of thumb is 50 square inches per second of belt gives 1 uA of current  for a self-charging VDG.

[pianomanjcb]

Hello Haversin,

Thank you for the advice. Silly me forgetting to add a ground connection to my lower brush. I grounded that brush and charge began building on the top brush. That being said, I still aim to improve the design further.

Would you recommend using a different material for the top roller? A material that might not be so prone to charge leakage? Like Nylon?

My current plan was to have a large PVC coupler (8in diameter) enclose the top roller area. I was going to 3D print some mounts to hold the coupler to the main PVC tube and then have a metal dome sit on top of the coupler (the metal dome being attached to the upper brush via a strip of brass foil). Do you think this would be an acceptable substitute to enclosing the top roller area inside the metal dome?

Thank you for the advice,
Jay

[haversin]

Hi Jay,

The fact that your upper corona brush is getting charged is a good sign! I would say not to change the rollers and go ahead with you build. Did you get a chance measure the short circuit current ? The level of this current is a good indicator of how well the charging system is working and allows for easy evaluation of different roller surface materials.

It's very important that the top terminal of the VDG fully enclose the top roller and corona brush. It's the Faraday ice pale effect that allows the VDG to attain very high voltages. If your married to the coupler idea I guess you could try lining the inside of the coupler with aluminum foil and then connect the foil to the top terminal. You will then have to deal with the corona leakage from bottom edge of the foil at the coupler.

Russ

[pianomanjcb]

Hey Russ,

I have not checked the current yet. I tried but the value was fluctuating because my device shakes when it runs (I'll fix that).

I am not stuck on the coupler idea, it was just a solution that didn't involve cutting into my IKEA bowls.  What do you think about using a metal paint can to enclose the top roller and brush, and then mounting the dome to the can? You can find a picture of this idea here:https://drive.google.com/drive/folders/1Do202KY-32-uGZIv8u-y8K7p_Y3Rfrl3?usp=sharing. It's the picture called "paint can idea". I would just need to find a way to prevent (as best as possible) discharge from the bottom edge of the can.

Here is the link to a can I can get a home depot just for reference: https://www.homedepot.com/p/BEHR-1-gal-Metal-Paint-Bucket-and-Lid-96601/100038785

Thanks for your help,
Jay

[haversin]

Jay,
  It's funny you mentioned IKEA bowls, I have two 14 inch IKEA bowls just sitting for the same reason.
I like the paint can idea, the bottom edge of the can will limit the dome from reaching it's full potential
(very bad pun intended). A toroid with a smooth surface could be placed at this edge and it wouldn't have to made of metal, it could be made of wood or non-conducting material coated with conductive paint. Probability not a good idea to draw sparks from it however.

Nice drawing of the paint can idea what software did you use to make it?

Russ

[pianomanjcb]

Russ,

I am using two 11" IKEA bowls for my generator. If this generator works well I may upgrade to a larger bowl like 14". I will design a 3D printable toroid to place around the rim of the paint can. I am curious, what is the reason the toroid needs to be coated with conductive paint? My initial reaction would have been to insulate the rim as much as possible.

Thanks, the software I use to model is Solidworks. It helps me plan my build out beforehand and i can 3D print custom parts which is so convenient.

-Jay

[Mads Barnkob]

I am following your project and will use some of your ideas and solutions in building my own

I like the idea of 3D printed parts and the brushes, is the ends sharp/pointy enough to be used as spray?

To get an idea of my project, I got a large top terminal about 80 cm in diameter, spun aluminium "toroid" shaped as a mushroom.

[Teravolt]

if anbody is interested they have large stainless garden orniment spheres on ebay. I found two that are about 400 mm on ebay. I also googled it to. they are a little pricy but I was able to stack 2 of them and get 3ft arcs. you can get them relitively cheap for a table top VDG

[Mads Barnkob]

if anbody is interested they have large stainless garden orniment spheres on ebay. I found two that are about 400 mm on ebay. I also googled it to. they are a little pricy but I was able to stack 2 of them and get 3ft arcs. you can get them relitively cheap for a table top VDG

They are called "gazing balls" or "pond balls" if anyone is wondering how to find them

[haversin]

Jay,
Covering the edge with a better insulator than air is certainly an option. It's been my experience with the VDG that increasing the effective radius of curvature of the edge works better. However I'm not an expert in HV insulation. Wood works for the toroid because at the HV and low current the VDG produces most types of wood act like a conductor.

To get an idea of my project, I got a large top terminal about 80 cm in diameter, spun aluminium "toroid" shaped as a mushroom.

Wow that's going to be a monster!
Where did you get this terminal from?

[pianomanjcb]

I am following your project and will use some of your ideas and solutions in building my own

I like the idea of 3D printed parts and the brushes, is the ends sharp/pointy enough to be used as spray?

To get an idea of my project, I got a large top terminal about 80 cm in diameter, spun aluminium "toroid" shaped as a mushroom.

Hey Mads,
I'm glad to be of some inspiration! The brush has many sharp ends and the entire brush is made of metal, I believe it will perfect for spray. With a terminal at 80cm you'll make Zeus jealous.


Russ,
That makes sense. I'm going to print a toroid and cover it in aluminum tape. And an update, the paint can design is working out very well.