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
modifications that I'm offering in this text. Sorry Bert! Your design
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
kilovolt range and I didn't feel like paying large sums of cash for
voltage capacitors. To build a bank of electrolytic capacitors for my
begins at around $180. For less than $30 I can build several oil filled
with many times the storage capacity per $ of those nasty commercial
electrolytics. Sure, electrolytics take up less space, but who cares
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
beating on a couple with about 7.5 kv for a couple of weeks with no
I used the second one about 20 minutes after filling it with oil and
performs just as well as #1 does (go figure).
You need 4 mil or 6 mil poly sheeting from the hardware store and a
roll of aluminum foil from the wife's kitchen cabinet. These plans are
exact and may be modified to suit whatever needs you may have. Just
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
- A length of 2" O.D. (or 3", 4", 5", etc...)
- 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
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
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.
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
will sit on top of this to keep them out of moisture that may collect
If your using 2" pvc then the lengths I'll suggest will work nicely.
them up for larger pipes. Cut two 13 foot lengths of poly sheeting that
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
and feed the stripped end down through the tube and out the notched
the wire at the base of the stripped end and hook it in the notch so
bare wire rests against the outside of the tube and the insulated part
wire > ========================================================\
Lay out one 13 foot poly strip and tape down both ends to the floor
two tiny pieces of tape (this is tempory to stabalize construction).
your foil down the full length of poly. Leave even spacing on both sides
overlap the poly on one end by 1". Tack this in place at each end
(again, only a little because this is temporary).
Now place the second length of poly sheeting directly over the first
ends to hold in place). Unroll another layer of foil, but overlap edge
on opposite end from the first layer. Wrap the overlap from the top
around the 1/2 " pvc and wire assembly so that the bare wire contacts
foil. Remove tack tape on this end and begin rolling the aluminum/poly
sandwich up on the pvc/wire assembly. Keep everything straight when
When you reach the far end you should have a little foil hanging out
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
so that is doesn't unroll. This will also hold the wire onto the side.
cinch the ties any tighter than it takes to hold everything in place
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
corner to corner in both directions (like the letter x). This will allow
plexi to crack if there's ever a sudden pressure build-up due to capacitor
Place roll into the 2" pvc assembly and place plexi cap on pipe.
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
the capacitor. Feed the bolts through so that the threaded ends stick
top and attach the wires underneath. Seal the bolts in from top and
with RTV. Seal vacuum fittings in place with RTV.
Coat the top edge of the pvc pipe with RTV and seal down the plexi
Close one vacuum fitting and apply a light vacuum to the other. Listen
hissing and seal any leaks. If oil escapes you'll have a real nice mess.
the RTV cure for 24 hours.
Now run some hose from the other vacuum fitting into the bottle of
apply vacuum. The oil will be sucked into the capacitor. Stop filling
oil is about 1/4" over the edge of the poly. Seal off the second
fitting and continue applying vacuum to the canister. Don't let the
up into the vacuum hose to the pump. This will destroy your pump. Run
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
This gives it time to release any remaining air. If you promise not
more than 5kv then you could probably use it immediately. My first tests
using a DRY rolled capacitor just to see what it would take before it
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
until you reach the breakdown point. This will be your PEAK voltage
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
shouldn't have any problems. If you want more voltage then put several
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
Capacitors in series : Ct = --------------------
1/C1 + 1/C2 + 1/C3 ... etc.
Capacitors should stand vertically in a metal pan. This catches oil
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!!!