Saltwater Capacitor Construction

The reason that homemade capacitors are used in the ASTROD is that commercial ones that can withstand the high AC voltages are very expensive - as much as hundreds of dollars each.

Alan Trent can provide information on factors and equations for determining capacitance based on the type of bottle used and the construction of it. I prefer to merely build one and put it on a capacitance meter to determine its value.

Parts List
Wine bottle
Bare 8 ga wire
Aluminum foil
Electrical tape
Mineral oil
No. 2 Airlock stopper
Epoxy, Goop, or silicone caulk

750ml size is used for the wine bottle. Get one that has a concave bottom (punt). This adds to the strength of the bottle. The best are from champagne or lambic (sweet, fruity beer) since these are made to withstand pressure and are typically 750ml.

The bare 8 ga wire is from Home Depot. It is grounding wire sold on a spool by the foot. Get about 3 feet for each cap.

No. 2 airlock stoppers are rubber corks with a hole in the middle, meant to accept an airlock and be placed on a standard wine or beer bottle. They are available at wine and beer making shops.

Dissolve salt in approx 750ml hot water to saturation where no more salt can be dissolved.

Put saltwater into bottle to 4" from top. Place stopper on top. Put 8 ga bare wire through hole in stopper so it touches the bottom and extends 4" or so over top. Using syringe or small funnel, put mineral oil in through the small hole to about 2" from top.

It is necessary to put mineral oil in after the wire since if it is done before, the wire will become coated as it passes through and it will not work well since it won't make good contact with the saltwater. Important - there must be at least 1" or so empty space between the top of the oil and the bottom of the stopper to allow room for expansion. Since the bottle is sealed airtight, it can explode in high temperatures without room for expansion. The capacitors do not generate heat themselves in my setup during operation, but if the device is enclosed the temp will rise due to the transformer and spark causing heating.

Seal top with epoxy or other competent adhesive to prevent leakage and hold stopper to bottle.

Cut other bare wire to approx 5" more than bottle height. Bend it so it matches the contour of the bottle vertically. It runs from the bottom to within a few inches from the top along the side of the bottle. Do not let it get too close to the wire coming out the top, put a couple stripes of tape around to hold it down.

Fold 4 feet of alunimum foil in half lengthwise. Wrap this around the bottom portion of the bottle tightly. Wrap over this with the more electrical tape, or other strong tape. Even though tape covers the aluminum foil and provides some insulation, one can still get shocked by touching the wrap when in operation. If the wine bottles are used in a manner where the wrap portions are different potentials and are placed near each other, a spark will jump through the insulation and melt the tape and possibly cause an explosion hazard from excess heat as well as destroy the transformer. If they are going to be close to one another, make a frame to hold them down, or do as I did and that is to use the insulating foam in a spray can to fill around the bottles to hold them down and keep them separated.