Kliest and Musschenbroek: 1745

Capacitors were discovered in 1745 by Ewald Christian von Kliest and Pieter van Musschenbroek. There is a lot of text out there about the discovery. Most of it is very interesting:

“When the globe D is made of English glass there is no effect, or almost none; German glass must be used, Dutch doesn’t work either; D does not have to be a globe, a drinking glass will do; nor does it matter if it is large or small, thick or thin, tall or short, or of any particular shape; but it must be made of German or Bohemian glass. The globe D that almost killed me was of very thin white glass, five inches in diameter.”

This is another important example of the discovery of a subatomic phenomena which affects our daily lives by individuals who were not a part of “big science.” Experimentation and observation have always been keys to discovery.

I’ve been making glass jar capacitors since I was in fifth grade (no, I am not certain if plastics had been developed then. Yes, we had electricity.). Here’s the basic formula for calculating the capacitance for Leyden Jar Capacitors (DIY’s or those found in museums):

C = 0.224 Π K D (H +0.25D) / 1,000,000 T

C = capacitance in microfarads
K = dielectric constant
D = diameter of jar in inches
H = height of jar in inches
T = thickness of jar in inches

I’ve been making plate glass capacitors for projects since. I’ve had a desire to make larger capacitors using plastic to reduce weight and resist breakage. I settled on relatively easily available materials. These include polypropylene (8 mil carpet liner) as a dielectric, PVC pipe for the housing (pulled from the dumpster at ITP after a recent Maker Fair), Aluminum foil, and some hardware that I just knew I would need (?) that I brought from my studio in San Diego. I used hardware larger than was really needed for issues of mounting safety: There is little to be gained in underbuilding an experimental object. This is especially true for me as I am extremely clumsy. Aside from the availability of the polypropylene, the material is a homopolymer whose heavier mass and density are useful for the higher voltages I will be using.

Images below show the PVC caps drilled and prepped for hardware. Next steps in the assembly are rolling the Aluminum foil and polypropylene, and the decision to use wax or mineral oil to fill the tubes. Each has its advantages and disadvantages.