This is all
Ikea's fault !!..
My wife spotted their new Blanda
Blank Bowls, each one is an almost perfect hemisphere 50mm in diameter
and they come in packs of 4.
They NEED an application...
(I've since read Ikea's description and the
packaging they come in and I still have no idea what they are
supposed to be
used for ?, eggs? ,spice?, HV
After some thought of what
good for, the idea of a small Van De Graff came to
The VDG'let was
||The top Sphere of the VDG'let was made
from two bowls (as above) .
The lower half was drilled with
a 20mm hole to allow mounting to black 20mm electrical trunking which forms
the supporting column.
The top of the trunking was cut
in a V to allow a 2mm brass rod to sit across the center of the tube.
This rod carries a 2.5mm id aluminium tube that is freely spinning. As the
bottom roller is also made of aluminium this roller is coated with PVC
tape to ensure it will take a different polarity charge than the lower
end. See the Tribo electric Series
The trunking was attached to the
bowl with a lump of epoxy putty and the roller secured in place
with a 10mm long sawn off peice of PVC trunking
Be careful, drilling large
holes in small pieces of stainless steel is not for the faint
|| The top hemisphere (bowl)
contains the pickup comb. This is a peice of stranded wire bent to a fan
shape and stuck into the bowl. This is arranged so when the
two halves of the sphere are together the wires just miss
the roller beneath.
||The belt is made from
a peice of latex rubber
cut from the wrist of a medium latex
The length of the supporting
column has been arranged so this belt fits nicely from the
bottom to top rollers so there dosn't have to be a join.
The best way of cutting this
strip is to insert a business card into the wrist part of the glove, and
cut an 8mm strip through glove and card. This is not as easy as it sounds,
I trashed a number of gloves before getting this right.
Bottom box contains a
12v DC motor crudely attached so its position can easily be
changed to keep the belt in the centre
of the trunking.
The motors shaft has been
extended with an aluminium tube, this is in direct contact with the
Another earthed comb made from
stranded wire is placed near the belt.
Another hemisphere is used here
to shape the electrical field (ok, so it looks good and you do get 4 to a
packet) Idealy the motor should be within this hemisphere, but I couldn't
get a motor small enough. and mounting a motor to a hemisphere is much
|Picture of it working.
Use your imagination
|| The the VDG fired up first time
I can get about
22mm sparks from the spheres in good dry air (difficult to
find in the uk !) Charging current is
an estimated 0.5-1uA
I have tried using other materials for the rollers,
but PVC-Latex-Aluminum appears to work as the best combination (so far). I'm
looking for some sort of nylon roller to replace
the aluminium one if possible.
In really dry air I
can get the sparks to track all the way from top to bottom via the PVC
column, but this is rare so I'm not going to try to insulate the
Update : I now offer a Van De Graaff based on this device as a kit
Tesla Coils and High Voltage