Photo credit: Dake and Wiki commons.
The generator outlined here has proven to be a
very solid and simple design, and I’ve used the
design in talks and presentations over the years
Built as described, this generator will produce a
solid one inch (or more) spark to the finger every
second or so, and can reach much higher charges if
Long hair will stand on end if you touch the
generator while standing on an insulator, and it will
quickly run motors and all kinds of electrostatic
gadgets; including stunts I’ll mention later.
Motor and Roller
The motor is a 1,700 rpm 1/40th hp motor
which I found in a surplus store for about $15.
Virtually any motor will work since the motor is
running with almost no load.
I think the two most important parameters to
consider in selecting a motor are: the motor rpm,
and the diameter of the axle. Though I’ve built very
good generators with motors as slow as 600 rpm,
higher rpm motors will build up a charge faster and
overcome leakage problems — especially on humid days
when Van de Graaffs perform very badly in general.
In my personal experience, motors of over 5,000
rpm have caused my belts to “flap,” and required a
speed control to work well. However, if you are out to
build the optimum powerhouse of a generator, high-power commercial units generally try for belt speeds of
up to 6,000 feet a minute! Interestingly, belts speeds
above 6,000 feet a minute tend to blow electrons off the
belt, and you wind up with diminishing returns.
With regards to the motor axle size, I used a plastic
wheel from a furniture roller (Figure 3) for my lower
wheel. So, I simply looked for a motor with an axle
slightly larger than the axle on the roller so that the
wheel could be drilled and “friction fitted” on the motor
axle with a few hammer taps.
■ FIGURE 2.
■ FIGURE 3.
The insulating column is simply 3” PVC sewer pipe.
ABS pipe is not optimum (though it will work) as the
black coloring is slightly conductive. Acrylic or phenolic
pipe might provide even better performance, and are
handy being see-through.
Figure 4 shows a reverse view of my simple metal
support for the column, and a PVC sleeve I sliced
lengthwise and bolted to the support as shown. This
sleeve — combined with a hose clamp — keeps the
column ridged and straight, while also allowing you to
slide the main column up and down to accommodate
different belt sizes, and to adjust tension on your belt.
September 2012 43