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cbfull

Tue Jun 19 2007, 12:19PM

Registered Member #187 Joined: Thu Feb 16 2006, 02:54PM
Location: Central Ohio
Posts: 140

Thanks for the comments on my VDG design. Unfortunately I am in the process of trying to get my basement finished so I can have a workspace.

I can tell you that my column is approx 40 inches long, 5 inches diameter acrylic. It was a lucky find and was given to me for free. The terminal is a 12" diameter heavy gauge aluminum sphere, halves are taped, not joined. The thickness of the aluminum basically prevents me from turning in the lower edge to try and reduce the leakage at this point, but I have another SST 14" terminal on standby that I will also be working on.

I guess I have been lucky with the aluminum roller. I have never had a problem with the metal contaminating the belt, as far as I know.

I'll have to get some pictures of it soon.

Thanks Hammer.

Finn Hammer

Tue Jun 19 2007, 07:07PM

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

Today I did something fun!

Almost as fun as simulating a circuit in Spice. You know the thrill of trying out a circuit you could only dream about, certainly not build overnight.

I pulled out the frequency inverter drive, to increase the RPM on the motor.
At 120Hz, 7200 rpm, the contactor started to make non-standard noises, so that`s where I stopped it.
At that time I had 135uA on the clock.

I guess this pretty much sets the standard for small VDG`s.

Pelletrons anyone?

Cheers, Finn Hammer

ragnar

Wed Jun 20 2007, 03:03AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

That's an oh-so-subtle "1337", Finn

hehe

Antonio

Thu Jun 21 2007, 11:44PM

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

It seems possible to make a pelletron using as chain a string of beads, alternating conductive and insulating beads in an a strong insulating string. I can easily find chrome-plated plastic beads with 2 cm of diameter that look interesting for a demonstration machine.
For more current, parallel strings can be used.

Finn Hammer

Sat Jun 23 2007, 01:25PM

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

Antonio wrote ...

It seems possible to make a pelletron using as chain a string of beads, alternating conductive and insulating beads in a strong insulating string. I can easily find chrome-plated plastic beads with 2 cm of diameter that look interesting for a demonstration machine.

Building a pelletron would be interesting.
I wonder how is it possible to determine the current that can be delivered from a chain of a given dimension, and speed.
At pelletron.com they claim up to 200uA per chain.

The chains that I have seen, I would estimate to be only 20 mm in diametre, but perhaps bigger chains are available on the big machines.

Fermilabâ€™s Pelletron

Has these information:
************************************************* ******
Table T1: Charging System Parameters

Motor revolution frequency: 19.3 Rev/sec
Motor Power: 5.6 kW
Actual Load: ~0.5 kW
Nominal chain speed: 18.5 m/sec
Chain central diameter around sheaves: 30.5 cm
Distance between sheave centers: 3.68 m
Chain revolution frequency: 1.8 Hz
Length of a single pellet: 32 mm
Gap between pellets: 5.3 mm
Maximum voltage of charging PS: 60 kV
Charging efficiency in good condition: 7.3 ÂµA/kV
(based on two chains with charging at the ground and at the terminal)
************************************************* *********
60kV*7.3 = 438uA/2 = 219uA per chain.
But 60kV is very high for a hobby system.

The distance btwn pellets is also surprisingly short. I assume that the chain has to be very long due to this...

Antonio wrote ...

For more current, parallel strings can be used.

And the speed can be increased...

Cheers, Finn Hammer

Antonio

Sun Jun 24 2007, 11:19PM

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

Finn Hammer wrote ...

I wonder how is it possible to determine the current that can be delivered from a chain of a given dimension, and speed.
At pelletron.com they claim up to 200uA per chain.
60kV*7.3 = 438uA/2 = 219uA per chain.
But 60kV is very high for a hobby system.

These high currents are surely due to operation in a pressurized tank. The charging current
can be estimated as i=NfAp, where
N=number of pellets
f=chain rotation frequency
A=pellet external area
p=maximum charge density (26.55 uC/m^2 in air)
This assumes that the pellets leave the lower pulley with one half of the maximum charge
density and that there is a current doubler at the top pulley.
With the data that you list, and assuming a pellet diameter equal to the length, I
get 34.4 uA.

Finn Hammer

Mon Jun 25 2007, 06:02PM

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

Antonio wrote ...

These high currents are surely due to operation in a pressurized tank.

With the data that you list, and assuming a pellet diameter equal to the length, I
get 34.4 uA.

In that case, I am out.
I am a performance freak, and would rather build a 60cm toploaded machine with 300uA charging ability in atmospheric pressure with a polyurethane belt.

Cheers, Finn Hammer

Finn Hammer

Thu Jun 28 2007, 08:48AM

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

All,

Just to wrap this up.
Great fun was had when I delivered the VDG to it`s proper home, The Danish Electricity Museum.
Seen here is a guest checking it out.

With this machine, the guests can raise hair without getting shocked. They have to touch the terminal to get the belt running, so the approach to the machine is without agony. The machine stops charging as soon as they release the button, so they can get away from the machine without getting chocked either.

Cheers, Finn Hammer

Lyonel Baum

Thu Jul 12 2007, 03:45PM

Registered Member #894 Joined: Thu Jul 12 2007, 02:38PM
Location: Macon , France
Posts: 12

Hi all ,

More to come on embossing Vdg dome ...

Lyonel Baum

Lyonel Baum

Thu Jul 12 2007, 05:41PM

Registered Member #894 Joined: Thu Jul 12 2007, 02:38PM
Location: Macon , France
Posts: 12

Finn Hammer wrote ...

The distance btwn pellets is also surprisingly short. I assume that the chain has to be very long due to this...

Antonio wrote ...

For more current, parallel strings can be used.

And the speed can be increased...

Cheers, Finn Hammer

Here are a picture of 3 pellets and a picture of a 2 chains NEC Pelletron

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