Dual Van de Graaff Generator
Nickel, Mon Mar 19 2018, 10:54AMSince seeing Nickademus's VDG many moons ago, I've gone rash and built a pair of them for my own amusement. I've taken dozens of pics of parts in the making and will be happy to answer any questions.
It is also my first attempt at taking video using my phone. (Galaxy S2) A bit shaky at first, until I put the phone on top of my lathe head-stock, being the nearest safe place for it.
Have a look, see what you reckon!
Re: Dual Van de Graaff Generator
Nickel, Thu Mar 22 2018, 09:36PM
I have now tried the pair of them together, but not getting the result I'd hoped for. With the domes 12" apart, they just sit there sizzling like two angry demons, occasionally 'popping'. With the domes 18" apart, they just sit there sizzling, occasionally 'popping'.
Am I expecting too much? I know they are both generating the max for 12" dome, ie +450kV, but no nice big fat snapping sparks.
After a bit of thinking perhaps this is the trouble:
The terminal capacitance for each unit is ~17pF.
I am trying to put two of them in series, so total capacitance is 8.5pF
With a potential difference of 900kV, as soon as the air-gap starts to break-down, there is insufficient capacitance to sustain the plasma, and the voltage drops sharply, so no "big bang".
I've left them alone in the Wshop for a while, because the radio was getting nervous and upset and kept changing channels; also my RS485 link controlling the solar MPPT/PV kept dropping off, and upsetting the PC indoors.
If anyone has any bright ideas (Finn?), please let me know, otherwise they go in a box until my enthusiasm peaks again!
Nickel, Thu Mar 22 2018, 09:36PM
I have now tried the pair of them together, but not getting the result I'd hoped for. With the domes 12" apart, they just sit there sizzling like two angry demons, occasionally 'popping'. With the domes 18" apart, they just sit there sizzling, occasionally 'popping'.
Am I expecting too much? I know they are both generating the max for 12" dome, ie +450kV, but no nice big fat snapping sparks.
After a bit of thinking perhaps this is the trouble:
The terminal capacitance for each unit is ~17pF.
I am trying to put two of them in series, so total capacitance is 8.5pF
With a potential difference of 900kV, as soon as the air-gap starts to break-down, there is insufficient capacitance to sustain the plasma, and the voltage drops sharply, so no "big bang".
I've left them alone in the Wshop for a while, because the radio was getting nervous and upset and kept changing channels; also my RS485 link controlling the solar MPPT/PV kept dropping off, and upsetting the PC indoors.
If anyone has any bright ideas (Finn?), please let me know, otherwise they go in a box until my enthusiasm peaks again!
Re: Dual Van de Graaff Generator
Sulaiman, Fri Mar 23 2018, 09:28AM
Does one vdg produce a positive voltage and the other negative ?
If not then I would not expect inter-vdg arcing :)
Sulaiman, Fri Mar 23 2018, 09:28AM
Does one vdg produce a positive voltage and the other negative ?
If not then I would not expect inter-vdg arcing :)
Re: Dual Van de Graaff Generator
Nickel, Fri Mar 23 2018, 11:16AM
Yes; one VDG positive terminal, the other negative terminal. The bottom charge-combs are connected together and to ground. This gives +450kV on the positive terminal with respect to ground; ie electron starved.
The negative is at -450kV with respect to ground, ie electron surplus.
The potential difference between the two terminals should therefore be 900kV with respect to each other.
I have noticed that when a spark occurs, it does not go the whole distance between the globes, but appears to spark to an invisible sphere surrounding the electron-surplus globe. This happens with both of the units; the electro-negative sphere develops it's outer charge-sphere that the electro-positve sphere sparks to.
Where the spark meets the charge 'sphere' it stops and becomes a mauve cloud of what I assume to be corona discharge.
Next job is to build a pair of 5 gallon Leiden/Leyden jars to up the capacitance of the system.
Nickel, Fri Mar 23 2018, 11:16AM
Yes; one VDG positive terminal, the other negative terminal. The bottom charge-combs are connected together and to ground. This gives +450kV on the positive terminal with respect to ground; ie electron starved.
The negative is at -450kV with respect to ground, ie electron surplus.
The potential difference between the two terminals should therefore be 900kV with respect to each other.
I have noticed that when a spark occurs, it does not go the whole distance between the globes, but appears to spark to an invisible sphere surrounding the electron-surplus globe. This happens with both of the units; the electro-negative sphere develops it's outer charge-sphere that the electro-positve sphere sparks to.
Where the spark meets the charge 'sphere' it stops and becomes a mauve cloud of what I assume to be corona discharge.
Next job is to build a pair of 5 gallon Leiden/Leyden jars to up the capacitance of the system.
Re: Dual Van de Graaff Generator
Sulaiman, Fri Mar 23 2018, 11:23AM
I imagine that you are producing some kind of continuous discharge between the two vdg. that reduces the available voltages.
Try larger and smaller separation ?
Sulaiman, Fri Mar 23 2018, 11:23AM
I imagine that you are producing some kind of continuous discharge between the two vdg. that reduces the available voltages.
Try larger and smaller separation ?
Re: Dual Van de Graaff Generator
Conundrum, Fri Mar 23 2018, 11:39AM
Maybe use a properly shielded camera? S2 isn't bad but I've had problems with EMI on these.
I came up with a variant of this using a camera such as the u1010 which has a metal shield so in theory should be far less susceptible to EM related problems.
Conundrum, Fri Mar 23 2018, 11:39AM
Maybe use a properly shielded camera? S2 isn't bad but I've had problems with EMI on these.
I came up with a variant of this using a camera such as the u1010 which has a metal shield so in theory should be far less susceptible to EM related problems.
Re: Dual Van de Graaff Generator
Nickel, Fri Mar 23 2018, 12:42PM
Sulaiman, I think you are probably right about the possible continuous discharge. At the moment I try to keep my workshop at 40% RH or below, to protect my tools and machines.
I'll try moving them further apart, to see what happens. It seems that the electron-cloud that surrounds the negative terminal is big enough to bleed voltage down to ground and surrounding earthed machinery, as well as any objects nearby. If I stand within 3 feet of either terminal when they are running individually, I get charged up either way, + to the point that sparks sneak from my feet, through the sides of my boots to the workshop floor. Amusing and tickling, but not what I set out to do.
The next thing to try is corona-reduction at the entrance holes to the terminals. I have experimented with 22mm copper central-heating pipe, but that is still work in progress. I've wasted a lot trying to achieve a re-entrant curve, so there is only cable-sheathing split to go over the edges of the hole.
Until I do a bit more shielding of electronic stuff, I have put a hold on operations. I have a roll of 2" chicken-wire fence to make temporary earthed cages around the more expensive stuff.
In the meantime, here's a lower spray comb:
Nickel, Fri Mar 23 2018, 12:42PM
Sulaiman, I think you are probably right about the possible continuous discharge. At the moment I try to keep my workshop at 40% RH or below, to protect my tools and machines.
I'll try moving them further apart, to see what happens. It seems that the electron-cloud that surrounds the negative terminal is big enough to bleed voltage down to ground and surrounding earthed machinery, as well as any objects nearby. If I stand within 3 feet of either terminal when they are running individually, I get charged up either way, + to the point that sparks sneak from my feet, through the sides of my boots to the workshop floor. Amusing and tickling, but not what I set out to do.
The next thing to try is corona-reduction at the entrance holes to the terminals. I have experimented with 22mm copper central-heating pipe, but that is still work in progress. I've wasted a lot trying to achieve a re-entrant curve, so there is only cable-sheathing split to go over the edges of the hole.
Until I do a bit more shielding of electronic stuff, I have put a hold on operations. I have a roll of 2" chicken-wire fence to make temporary earthed cages around the more expensive stuff.
In the meantime, here's a lower spray comb:
Re: Dual Van de Graaff Generator
Nickel, Wed Mar 28 2018, 08:47AM
I had a play outdoors last night with the positive unit in the semi-dark. This has shown up where my losses are going. As many have found before me, the entrance to the top sphere needs to be a re-entrant curve to stop corona losses.
Outside in the dark, the base of the dome shows a continuous weak 'spark' pointing towards the ground. After 1 inch, this becomes a mauve 'cloud' about 2-3" diameter, 6-8" long pointing ground-wards.
My tube-bending skills are not up to crease-free bends for tight radii, so any ideas or sources for a corona-prevention torus would be appreciated.
Nickel, Wed Mar 28 2018, 08:47AM
I had a play outdoors last night with the positive unit in the semi-dark. This has shown up where my losses are going. As many have found before me, the entrance to the top sphere needs to be a re-entrant curve to stop corona losses.
Outside in the dark, the base of the dome shows a continuous weak 'spark' pointing towards the ground. After 1 inch, this becomes a mauve 'cloud' about 2-3" diameter, 6-8" long pointing ground-wards.
My tube-bending skills are not up to crease-free bends for tight radii, so any ideas or sources for a corona-prevention torus would be appreciated.
Re: Dual Van de Graaff Generator
Nickel, Sat Nov 17 2018, 04:35PM
I've been doing a lot of thunking recently, and intend to resurrect my project. Research on electrostatics shows there will be a field-concentration where the column enters the top sphere. The cure is to form a re-entrant curve to the dome at the column entry point.
After many failed attempts to make this using assorted bits of pipe, The answer leapt out at me from the window of a catering supply shop of all places!
It's called a 'Bundt pan/tin', 'Savarin mould', or 'Kugelhopf pan'.
A lot of them are fluted, which is no good at all.
The one to look for is a plain one, available in all sorts of sizes, with one for everyone's application!
A simple hemispherical bowl inverted on top of it will provide exactly what is needed:
Google
Nickel, Sat Nov 17 2018, 04:35PM
I've been doing a lot of thunking recently, and intend to resurrect my project. Research on electrostatics shows there will be a field-concentration where the column enters the top sphere. The cure is to form a re-entrant curve to the dome at the column entry point.
After many failed attempts to make this using assorted bits of pipe, The answer leapt out at me from the window of a catering supply shop of all places!
It's called a 'Bundt pan/tin', 'Savarin mould', or 'Kugelhopf pan'.
A lot of them are fluted, which is no good at all.
The one to look for is a plain one, available in all sorts of sizes, with one for everyone's application!
A simple hemispherical bowl inverted on top of it will provide exactly what is needed:
Re: Dual Van de Graaff Generator
Nickel, Tue Nov 20 2018, 09:37PM
I've just found this lovely machine on the youtube:
Well worth a look if you are a crackle-addict!!
Nickel, Tue Nov 20 2018, 09:37PM
I've just found this lovely machine on the youtube:
Well worth a look if you are a crackle-addict!!
Re: Dual Van de Graaff Generator
Nickel, Thu Dec 13 2018, 09:17PM
I built myself a Leyden jar over the last 2 days. It's a spaghetti container from Asda's for £3.75 or so. 3M Ali tape from Lidl £2 a roll. Orfcut of welder cable, bit of 20mm electrical conduit, bit of 15mm copper pipe, all out of the scrap box, and 32mm cabinet knob from Screwfix £3.79 for two in a bag. Several yards of duct-tape over the outside to protect the foil.
I bought two spag-jars, intending to make a pair. They are polystyrene, so I don't know how well they'll work. if it doesn't, then the other one will get used for spaghetti.
Why the thick cable says you?
To get thicker fatter sparks, you need bigger currents. This cable keeps the ESR down, so currents of many tens of amps are possible, even if only for a fraction of a microsecond. The individual strands are distributed over the outer surface of the thing to suck as much current as possible.
Dimensions: 11" x 3,3/4". Both foils stop 5" from the top, so flash-over distance = 10"
Testing is the usual affair, balance everything on wobbly bits of wood and rolls of tape, experiment with distances and gaps etc.
Testing today is using the negative unit because it was nearest.
At some stage I'll put a video on the tube.
It is loud, and probably V - dangerous. (keeps one hand in pocket all the time when powered up due to dodgy ticker)
Curious effect happens when discharging the top sphere using the earth-wand/globe, I took a screen-shot from a slowed-down video; it shows streamers going up the inside and outside of the container.
Any suggestions to cause/reason?
Nickel, Thu Dec 13 2018, 09:17PM
I built myself a Leyden jar over the last 2 days. It's a spaghetti container from Asda's for £3.75 or so. 3M Ali tape from Lidl £2 a roll. Orfcut of welder cable, bit of 20mm electrical conduit, bit of 15mm copper pipe, all out of the scrap box, and 32mm cabinet knob from Screwfix £3.79 for two in a bag. Several yards of duct-tape over the outside to protect the foil.
I bought two spag-jars, intending to make a pair. They are polystyrene, so I don't know how well they'll work. if it doesn't, then the other one will get used for spaghetti.
Why the thick cable says you?
To get thicker fatter sparks, you need bigger currents. This cable keeps the ESR down, so currents of many tens of amps are possible, even if only for a fraction of a microsecond. The individual strands are distributed over the outer surface of the thing to suck as much current as possible.
Dimensions: 11" x 3,3/4". Both foils stop 5" from the top, so flash-over distance = 10"
Testing is the usual affair, balance everything on wobbly bits of wood and rolls of tape, experiment with distances and gaps etc.
Testing today is using the negative unit because it was nearest.
At some stage I'll put a video on the tube.
It is loud, and probably V - dangerous. (keeps one hand in pocket all the time when powered up due to dodgy ticker)
Curious effect happens when discharging the top sphere using the earth-wand/globe, I took a screen-shot from a slowed-down video; it shows streamers going up the inside and outside of the container.
Any suggestions to cause/reason?
Re: Dual Van de Graaff Generator
Nickel, Thu Dec 13 2018, 09:19PM
Some pics:
Nickel, Thu Dec 13 2018, 09:19PM
Some pics:
Re: Dual Van de Graaff Generator
Nickel, Thu Dec 13 2018, 09:22PM
Doesn't seem to like the pics. They are all well under 2M, any suggestions?
Lets see if the youtube link works!
Nickel, Thu Dec 13 2018, 09:22PM
Doesn't seem to like the pics. They are all well under 2M, any suggestions?
Lets see if the youtube link works!
Re: Dual Van de Graaff Generator
Nickel, Tue Jan 15 2019, 04:57PM
Now I have built 2 Leyden jars, Ive had a chance to play with the VDGs as a pair. With the increased capacity available at each top electrode I have now nearly achieved my original objective. The sparks are now nearer to 1 MV than they were before. Measure spark-gap is 300 mm, which I reckon is as good as a mega-volt! Once I have done the savarin/bundt-tin mod I'll be there. Have a look at my latest post, see what you think:
Nickel, Tue Jan 15 2019, 04:57PM
Now I have built 2 Leyden jars, Ive had a chance to play with the VDGs as a pair. With the increased capacity available at each top electrode I have now nearly achieved my original objective. The sparks are now nearer to 1 MV than they were before. Measure spark-gap is 300 mm, which I reckon is as good as a mega-volt! Once I have done the savarin/bundt-tin mod I'll be there. Have a look at my latest post, see what you think:
Re: Dual Van de Graaff Generator
jpsmith123, Wed Jan 16 2019, 03:21AM
I'm wondering, what did you use for the domes? Are they stainless steel "gazing balls"?
jpsmith123, Wed Jan 16 2019, 03:21AM
I'm wondering, what did you use for the domes? Are they stainless steel "gazing balls"?
Re: Dual Van de Graaff Generator
Nickel, Mon Feb 04 2019, 09:36AM
Yep, "gazing globes". They were on sale in Sainsbury's a few years ago for £25 each. As soon as I saw them, they were identified as Top electrodes/air capacitors.
The sensible public refused to pay for such a silly affectation, so they dropped the price to a tenner each, and I grabbed two 12" plus one 10", for the 'bargin' price if £20 to you sir, discount for quantity.
Most of the bits have been lurking in my "future projects drawer" until ready for construction.
The Leiden jars are beginning to leak and track now; Polystyrene struggles to withstand 450kV across 2mm. I'll give them a wipe-down with IPA and see.
Next project is a 1 nF condenser to hang between the globes. 8" PVC sewer-pipe is my first choice for the experiment; with 6mm wall thickness it should withstand over 1 MV for a long enough to make some big fat sparks.
Just got to contact someone on a big building/construction site and wave a tenner!
Nickel, Mon Feb 04 2019, 09:36AM
Yep, "gazing globes". They were on sale in Sainsbury's a few years ago for £25 each. As soon as I saw them, they were identified as Top electrodes/air capacitors.
The sensible public refused to pay for such a silly affectation, so they dropped the price to a tenner each, and I grabbed two 12" plus one 10", for the 'bargin' price if £20 to you sir, discount for quantity.
Most of the bits have been lurking in my "future projects drawer" until ready for construction.
The Leiden jars are beginning to leak and track now; Polystyrene struggles to withstand 450kV across 2mm. I'll give them a wipe-down with IPA and see.
Next project is a 1 nF condenser to hang between the globes. 8" PVC sewer-pipe is my first choice for the experiment; with 6mm wall thickness it should withstand over 1 MV for a long enough to make some big fat sparks.
Just got to contact someone on a big building/construction site and wave a tenner!
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