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HV mod for a Van Der Graff Generator

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LAN_403

HighVoltageProjects

Fri Sept 19 2014, 03:18PM

Registered Member #9770 Joined: Wed Jan 23 2013, 01:42AM
Location: Wymondham, Norfolk, UK
Posts: 11

Hi All I have a VDG and have heard that you can add an extra brush powered by a HV DC supply to spray + (positive) charge to the already charging + belt .the electrons from the supply attract to the belt and make much more power.

I've looked everywhere and cant find what type of voltages this requires for this ,so cant decide on a transformer to use .

If anyone knows what TX , supply voltages and I guess Watts too is normally used I would very much appreciate it .

I've tried a board from a plasma ball (LOPT or Flyback ) it worked to a degree but its not very powerful and has no - (negative ) .Generally there needs to be + for the brush that sprays the electrons and a - that would go to earth on the VDG .

Thank you in advance . John

Wastrel

Fri Sept 19 2014, 05:13PM

Registered Member #4095 Joined: Thu Sept 15 2011, 03:19PM
Location: England.
Posts: 122

The VDGs I've seen have slowed down a lot when reaching full charge, I would expect these to be power limited by the motor.

Adding a charging brush say 5kv 10-100uA would allow you to remove the friction charger which would free up a bit more power.

Finn Hammer

Fri Sept 19 2014, 05:17PM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: SkÃ¸rping, Denmark
Posts: 741

John,

Read this:

Cheers, Finn Hammer

Steve Conner

Fri Sept 19 2014, 05:57PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

A TV or monitor flyback should do. The modern ones all have a built in rectifier with positive DC output. A plasma ball driver has an AC output so it will do nothing.

Finn Hammer

Fri Sept 19 2014, 07:48PM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: SkÃ¸rping, Denmark
Posts: 741

In the VDGÂ´s that I have built, I have used a LOPT, as Steve says.
I used a 120Mohm resistor in series between LOPT and comb, to limit current and avoid arcs to the pulley. Arcs will carbonize the belt and make it conductive.
It is well worth the effort to build the third comb up top, to double the charging current, by loading electrons to the belt on the down run. The arrangement of this second comb can be seen on the document I linked to before.
The idea is, that you connect the "pick off comb" to the top pulley, and feed the positive charge from it to the top electrode, via a suitably large resistor, so that a voltage in the region of 10Kv will develop across it due to the charging current.
This places the top roller at a 10Kv potential higher than the electrode. By connecting a third comb to the top electrode and placing it close to the belt on the down run, corona will form on itÂ´s tips, but negative this time, and charge the belt negative, effectively doubling the generators current. Any serious VDG should have this.
You can see how this came out on the last batch I built here:

Cheers, Finn Hammer

HighVoltageProjects

Fri Sept 19 2014, 08:43PM

Registered Member #9770 Joined: Wed Jan 23 2013, 01:42AM
Location: Wymondham, Norfolk, UK
Posts: 11

Thanks for all he help guys .Much appreciated !!

Finn.... I don't really understand where everything goes like the LOPT .I know it should be fairly simple I'll use a ZVS but at low power and try to figure the picture out its a little hard to work .

Oh and your VDG is amazing !!!

Antonio

Sat Sept 20 2014, 02:22PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

Instead of spraying charge in the belt and grounding the lower roller you can just bias the roller at high voltage and ground the spraying comb. This doesn't require any current from the power supply, except for leakage. A small electrostatic generator can be used as bias source.

HighVoltageProjects

Sat Sept 20 2014, 02:51PM

Registered Member #9770 Joined: Wed Jan 23 2013, 01:42AM
Location: Wymondham, Norfolk, UK
Posts: 11

Thanks Antonio . I don't understand though ,sorry !!

My field has been in Tesla coils for years and this is my first VDG .My top roller is the metal one and bottom is plastic .What kind of small electrostatic generator are you thinking I could use ? most things that I think of don't like being run open circuit .

My bottom comb is earthed .

I will add some pictures so you can see it ,Notice the top metal roller is on a plastic spindle though so making a brushed connection to it would be very hard for me

Thanks again guys all this info is invaluable ,I WILL learn this

Antonio

Sat Sept 20 2014, 03:14PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

Any electrostatic generator works in open circuit. For the bias generator you can use a friction generator, a Wimshurst machine, or any other that keeps constant polarity. Of course, and electronic power supply can be used, as one taken for a negative ion generator. The lower roller must be conductive (metal, wood) and insulated. Just connect the bias generator to it, and the bias charge will attract charges from the ground through the comb. All the energy for the operation is then provided by the motor turning the roller.

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