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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 &
flashing)
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
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Adam Smith
absmith-at-tiac-dot-net
Epoch, Inc. Digital Music Project
www.tiac-dot-net/users/absmith/ MP3 Demo Tracks Now Available!
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