Plastic soda bottles for bypass caps?

From: 	Adam[SMTP:absmith-at-tiac-dot-net]
Sent: 	Saturday, December 06, 1997 8:24 PM
To: 	tesla list
Subject: 	Plastic soda bottles for bypass caps?

I know that plastic soda bottles make for poor tesla tank capacitors, but 
it seems to me that that you could make some decent bypass caps from the 
lossy material (PET).  I was flipping through surplus catalogs looking 
for doorknob caps for my bypass caps, and found that the size I am 
looking for (200-300pF -at- 20kV) would run my around $40 each, and I need 
2!!! $80, I don't think so.  With kitchen Aluminum foil and a few pepsi 
bottles, I should be able to make 250pF caps that are quite small and 
practically free! Anything I am missing?

I tested out some pepsi bottle material, and a single thickness (10-12mil 
I think) doesn't puncture with 25,000 VDC on it- good, since I will only 
have 4.5kVAC on it in use.  Plus, with a thickness of 10 mils, and k=3.0, 
I work out that the plates have to have only 4 square inches of overlap.  
Here is my calculation:

e0 = 8.85418781762 * 10^-12 (dielectric constant of free space)
k = 3.0 (for polyethylene terphthalate)
1 inch = 0.0254 meters
Plates = two Al foil plates with 2" by 2" overlap area = 4.0 sq. in.

(e0 * k * 4.0 * 0.0254) / 0.010" = 270 pF (approx)


Adam Smith
Epoch, Inc. Digital Music Project

www.tiac-dot-net/users/absmith/                 MP3 Demo Tracks Now Available!