Re: My first cylindrical cap

From: 	Adam[SMTP:absmith-at-tiac-dot-net]
Sent: 	Sunday, December 14, 1997 1:36 AM
To: 	tesla list
Subject: 	My first cylindrical cap

Today, I decided to build some rolled caps, to see how easy/difficult it 
is and to use up the poly left over from building my flat plate cap, 
which was basically a real expensive mistake of a unit (>$200 for one 
cap!) Live and Learn.

I needed a 0.006uF cap for use with my OBIT powered coil, and would also 
like to be able to throw this cap into service on my 9kV 180mA coil.  
What I built was a Bert Pool style unit, but scaled down.  This was very 
easy to build in about 3 hours.  Cutting and cleaning the LDPE was the 
longest stage, and it is best to let the bottom endcap on the PVC 
enclosure dry over a period of a few hours.  Here are the details:

0.006uF rolled LDPE and flashing capacitor
Dielectric = four 8" by 72" 30mil LDPE strips, 60mil between plates.
Flashing = two 6" by 72" strips cut from a 6" x 50 foot roll.
Oil: Mineral, USP.

COST BREAKDOWN: (Making 3 caps wastes no LDPE, no oil and less pipe & 
Most prices are from my local Home Depot, except the LDPE from commercial 
plastics Somerville MA, and the Mineral Oil from the grocery store (from 
laxative aisle :-)
Material:                         Cost for 1 Cap     Cost for 3 caps

LDPE 30mil 4' by 8' sheet          1 sheet / $12      2 sheets / $24.00
6" by 50' roll of flashing         1 roll  / $10      1 roll   / $10.00
4" dia 10 foot PVC Drain Pipe      1 pipe  / $3.81    1 pipe   /  $3.81
4" PVC Drainpipe Flat Endcaps      2 caps  / $1.88    6 caps   /  $5.64
1/4" by 1-1/2" Brass bolt (2pk)    2 bolts / $0.75    6 bolts  /  $2.25
1/4" nuts (4 pack)                 4 nuts  / $0.75    12 nuts  /  $2.25
Rubber gasket (for around bolts)   2 gskt  / $0.50    6 gaskt  /  $1.50
16 Oz Bottles of Mineral Oil USP   2 bot.  / $5.78    5 bot.   / $14.45

Price Total:                                $35.47               $63.90
Price per cap:                              $35.47               $21.30

Expenses not listed:  Electrical tape to hold the cap once rolled (not 
enough room left for even the most modest of nylon cable ties), and PVC 
cement required to seal the bottom endcap.  I did not weld the top cap, 
because I am not building a bomb and I want to be able to repair the cap 
:-)  The friction fit alone is pretty air tight and oil tight, though I 
would not recommend operating the cap upside down or on it's side.  I 
also drilled a 1/2" blow hole in the top cap, plugged firmly with #1 
rubber stopper.  Safety first.

Ways to save more $$$:  You can use $2 roll of heavy duty aluminum foil 
instead of flashing, and you will save $8.

The reason for 72" strips of LDPE is that I have found this to be the 
longest size that can be used that will fit rolled up into a 4" ID tube, 
when using a total of 120mils.  If you have 6" ID PVC, you can use 8" by 
96" strips and get a 0.008 uF capacitor suitable for a 9kV 30mA neon, or 
you can fit a 0.006 uF cap that uses 8" x 96" x 90mils between plates 
good for 12kV -at- 30mA.

If you need more capacitance or voltage in a single cap, you will need to 
venture beyond Home Depot to find 6" dia PVC and build a 10" flashing/12" 
LDPE or 14" flashing/16" LDPE capacitor ala the original Bert Pool 
design.  I would personally not recommend using more than 10kVAC with the 
60mil LDPE capacitor described above.


Adam Smith
Epoch, Inc. Digital Music Project

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