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BUILD A CHEAP 5 Kv CAPACITOR


This design is a variation on the more powerful capacitor designs introduced
by Bert Pool in CAPACITR.ASC. I can't really take any credit beyond the few
modifications that I'm offering in this text. Sorry Bert! Your design was
inexpensive but not DIRT CHEAP. I had to test the limits of my household
materials and stay within my research budget limits.

-------------------------------------------
; How to build a CHEAP CHEAP CHEAP ;
; 5 Kv Capacitor ;
; ;
; by Jon Snell ;
; ;
; 9/28/95 ;
-------------------------------------------

I've been working on various F/E experiments using pulsed HV in the low
kilovolt range and I didn't feel like paying large sums of cash for high
voltage capacitors. To build a bank of electrolytic capacitors for my purposes
begins at around $180. For less than $30 I can build several oil filled caps
with many times the storage capacity per $ of those nasty commercial
electrolytics. Sure, electrolytics take up less space, but who cares about
space when $$$ are at stake?! (especially on my budget)

This is a text on constructing an oil filled capacitor for holding 5-8 kv. It
seems to be quickly usable (within 1 week) without HV breakdown. I've been
beating on a couple with about 7.5 kv for a couple of weeks with no problems.
I used the second one about 20 minutes after filling it with oil and it
performs just as well as #1 does (go figure).

You need 4 mil or 6 mil poly sheeting from the hardware store and a good long
roll of aluminum foil from the wife's kitchen cabinet. These plans are not
exact and may be modified to suit whatever needs you may have. Just remember,
more surface area = louder BANG!

Formula for figuring Capacitance in pF:

C= 0.2235 * (KA/d) * (N-1)

C = Capacitance in pF
K = Dielectric constant of insulator
A = Area of one plate in square inches
d = distance between plates in inches
N = number of plates

Remember: mfd or uF = .000001 Farad
mmfd or pF = .000000000001 Farad


Parts list:

- A length of 2" O.D. (or 3", 4", 5", etc...) PVC pipe.
- A length of 1/2" pvc.
- 2 end caps for the PVC.
- PVC cement
- Clear silicone RTV
- #22 HV insulated solid aluminum wire (or Delco 440 ignition wire)
- Two 1/8" bolts 1 inch long with nuts
- A roll of 4 mil or 6 mil plastic sheeting from the hardware
store. Polyeurythane is the best for the $.
- A roll of household aluminum foil.
- 1/4 inch thick plexiglass
- plastic wire ties
- Mineral oil (from pharmacy)

This is fairly simple. Cut your pipe about 6 inches longer than your roll of
foil. Clean one end of the pipe and the inside of the endcap with alcohol.
Liberally apply the cement to the pipe end and twist the cap in to place to
securely seal the end. This is the bottom of the capacitor.

Cut two 1 3/4 inch long by 1 inch wide rectangles from the plexiglass. Cut a
center slot halfway through the width of each so that they'll fit together
like an X. Drop this assembly into the bottom of the pipe. Your capacitor guts
will sit on top of this to keep them out of moisture that may collect on the
bottom.

If your using 2" pvc then the lengths I'll suggest will work nicely. Scale
them up for larger pipes. Cut two 13 foot lengths of poly sheeting that are 4
inches wider than the width of the aluminum foil.

Cut a length of 1/2" pvc that is 1 inch longer than the width of the poly
strips. Cut a 1/4" notch in one end. Strip several inches of the aluminum wire
and feed the stripped end down through the tube and out the notched end. Bend
the wire at the base of the stripped end and hook it in the notch so that the
bare wire rests against the outside of the tube and the insulated part is in
the center.

pvc ______________________________________________

wire > ========================================================\
___________________________________________\___
=============================== /
bare wire

Lay out one 13 foot poly strip and tape down both ends to the floor with just
two tiny pieces of tape (this is tempory to stabalize construction). Unroll
your foil down the full length of poly. Leave even spacing on both sides and
overlap the poly on one end by 1". Tack this in place at each end with tape
(again, only a little because this is temporary).

Now place the second length of poly sheeting directly over the first (tape on
ends to hold in place). Unroll another layer of foil, but overlap edge by 1"
on opposite end from the first layer. Wrap the overlap from the top foil layer
around the 1/2 " pvc and wire assembly so that the bare wire contacts the
foil. Remove tack tape on this end and begin rolling the aluminum/poly
sandwich up on the pvc/wire assembly. Keep everything straight when rolling.

When you reach the far end you should have a little foil hanging out from
bottom layer. Strip the end of another piece of wire and roll the foil
overhang onto the bare area. Now use the wire ties and secure the whole roll
so that is doesn't unroll. This will also hold the wire onto the side. Don't
cinch the ties any tighter than it takes to hold everything in place or you
may damage the poly with the wire.

Cut a square of plexiglass that overhangs the end of the 2" pipe on all on all
sides. Drill holes for 2 vacuum fittings and 2 1/8" bolts.

-------------------------------
|\ / |
| \ bolt / |
| \ x / |
| \ / |
| \ / |
| vac \ / vac |
| x \ / x |
| / \ |
| / \ |
| / \ |
| / x \ |
| / bolt \ |
| / \ |
------------------------------

After drilling the holes then lightly score the surface of the plexi from
corner to corner in both directions (like the letter x). This will allow the
plexi to crack if there's ever a sudden pressure build-up due to capacitor
failure.

Place roll into the 2" pvc assembly and place plexi cap on pipe. Measure and
cut wires so that they will reach the bolts. Double check your measurements
before cutting wires. You don't want any mechanical stress on anything inside
the capacitor. Feed the bolts through so that the threaded ends stick out the
top and attach the wires underneath. Seal the bolts in from top and bottom
with RTV. Seal vacuum fittings in place with RTV.

Coat the top edge of the pvc pipe with RTV and seal down the plexi endcap.
Close one vacuum fitting and apply a light vacuum to the other. Listen for
hissing and seal any leaks. If oil escapes you'll have a real nice mess. Let
the RTV cure for 24 hours.

Now run some hose from the other vacuum fitting into the bottle of oil and
apply vacuum. The oil will be sucked into the capacitor. Stop filling when the
oil is about 1/4" over the edge of the poly. Seal off the second vacuum
fitting and continue applying vacuum to the canister. Don't let the oil foam
up into the vacuum hose to the pump. This will destroy your pump. Run the pump
for about 1/2 hour to get most of the air out.

Let the capacitor stand on the shelf for about 5 days before using it.

This gives it time to release any remaining air. If you promise not to use
more than 5kv then you could probably use it immediately. My first tests were
using a DRY rolled capacitor just to see what it would take before it fried.
Just use some of the material that's left over and make a small test
capacitor. Drop it in a plastic tube but leave it dry.

Using a 700-15000 volt variable D.C.inverter, steadily crank up the volts
until you reach the breakdown point. This will be your PEAK voltage rating. A
safe working voltage will be about 2/3 of your peak.

NEAT TESTS: Place a 12" by 12" poly square on tile floor.
Place a 10" by 10" foil square on the poly, attach HV lead.
One more layer of poly, and one more layer of foil. Attach
other HV lead to top foil layer. Now place one more sheet
of poly over it all. Apply HV DC and listen to the crackling
as the plates charge. Discharge and charge several times.
Now turn off the HV DC source and discharge plates fully.
Don't touch until foil plates have been shorted together!!
Pick the layers apart and notice how the charging makes the
poly and aluminum pull together in a fairly tight bond, forcing
the air from between the layers.

If you used 4 mil poly then don't use much more than 5 kv DC with this and you
shouldn't have any problems. If you want more voltage then put several of
these babies in series (i.e., 3 caps in series = 15 kv).

Paralleling them gives you the same voltage but greater capacity.
Series reduces capacitance but increases total voltage rating.

Ct = total capacitance

C1, C2, C3...etc. = capacitance of individual capacitors in circuit

Capacitors in parallel : C1 + C2 + C3...etc = Ct

1
Capacitors in series : Ct = --------------------
1/C1 + 1/C2 + 1/C3 ... etc.

Capacitors should stand vertically in a metal pan. This catches oil in the
event of a leak. It also acts as fire-proofing if a capacitor ignites
(unlikely but still possible).

NO WARRANTIES, GUARANTEES, OR ANYTHING ELSE EXPRESSED OR IMPLIED.
YOU BUILD THIS AT YOUR OWN RISK. HIGH CURRENT LEVELS IN THE LETHAL
RANGE ARE POSSIBLE. DISCHARGES FROM CAPACITOR CAN CAUSE SKIN TO
FRY OR EXPLODE (ouch). IT IS IMPOLITE TO DETONATE BUGS OR OTHER
TINY CREATURES WITH HIGH VOLTAGE. KEEP PETS AWAY!!!

 

 
     

 

 


 

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