THE HAWG CAPACITOR EXPERIMENTS

TEST FIXTURE A: the Test Article is connected across a 450VA, 15 kV neon sign transformer (NST) in parallel with a 2cm fixed spark gap. PVC pipe caps support the victim.

TEST ARTICLE : a 2 liter coke bottle with saturated saline inside, set inside a cut off gallon of fermented gatorade and salt. A dead ant was allowed to remain in the electrolyte. #14 Cu wire was immersed in the interior and exterior electrolyte.

TEST 1 : When the PSWC was clip leaded across the gap, the arc became a very loud and satisfying roar. The internal electrolyte level was about 2 in above the external level, and streamers were observed over the exterior of the dielectric in a band between the inner and outer electrolyte levels. Especially bright discharges were seen on the dielectric close to the outer electrode wire, and the test was terminated.

TEST 2 : Extra dielectric was placed as a spacer between the outer electrode and the bottle dielectric, and high voltage was reapplied. Corona and surface streamers were seen in the band previously mentioned. After about one minute, the PSWC shorted out very suddenly. A small dielectric puncture was found several inch below the surface, under a fragment of the bottle label.

TEST 3 : Another PSWC was prepared with a well-stripped 2l coke bottle. This failed after about 3 minutes at the inner (upper) electrolyte level by arcing thru to the outer electrode wire.

Conclusions : Everybody is right. Polyethylene Terpthalate is a great dielectric. Soda pop bottle PSWCs are vulnerable to dielectric rupture, puncture and leak. Foil is not the way to go.

Recommendations : Try again using a metal outer vessel for more symmetric current distribution, probably with a spacer covering the bottom to prevent dielectric stress concentration. Equalize inner and outer electrolyte levels. Use an oil layer above the electrolyte. Cleanliness is next to Godliness and Saint Tesla, get bottles 'squeaky clean' before use. Keep electrodes clear of dielectric to allow current density to diffuse thru electrolyte. Symmetric current diffusion and smooth, clean dielectric seem to be essential. No failures were attributed to the dead ant, although bits of label and glue were suspected in several failures.

TEST ARTICLE : Outer electrode and vessel was a cheap K-mart stainless steel stock pot, the bottom of which was lined with disk cut from plastic ceiling light grille. The soda bottle was thoroughly stripped and all label adhesive removed with methanol. The inner electrolyte started out as carbonic acid, magnesium sulfate and sodium chloride. The outer electrolyte was magnesium sulfate and sodium chloride in a solution of water and fermented Gatorade. The inner electrode was 10 inch of 1/2 in copper pipe suspended in the bottle neck by a copper tee. The dead ant from last night was retired from duty. Electrolyte levels were equalized within a mm, and no oil layer was added.

TEST 4 : The test article was connected in parallel with a 450 VA, 15,000 Volt NST bridged by a 2 cm static arc gap. During the test, intermittent streamers were observed on the upper dielectric, which mostly appeared internal. Some condensation was also observed on the internal surface. After several minutes the streamers subsided although condensation remained. The plastic bottle dielectric failed at about t+30 min, with a small rupture at the electrolyte surface. All components had about a 10 C temperature rise. A narrow band of plastic at the liquid surface had shrunk during the run, making a smooth, symmetrical groove or constriction all the way aroud the bottle at the liquid line. The groove was about one cm in width and depth. Crystalline deposits were also observed around the entire circumference.

This was the most reliable and longest lived plastic bottle capacitor tested.

RECOMMENDATIONS : Filter contaminants from electrolyte, use a mineral oil film on both electrolyte surfaces to reduce corona. This may aggravate heat accumulation at the top of the liquid level.

TEST ARTICLE : Same as test 4, but with 5mm mineral oil film on electrolyte surface inside and outside dielectric.

TEST 5 : The test article with oil layer was tested for 30 seconds. A slight foam of gas bubbles was generated around the dielectric at or near the surface. A milky cloud began spreading in the oil layer or interface which appeared to be composed of tiny gas bubbles. Two hours after the test, the milky layer had dissipated.

TEST FIXTURE B: The Test Article is connected in a standard TC circuit. The excitation is a 450VA, 15 kV NST in parallel with a 2cm fixed spark gap. A 40 in dia 10 turn solenoidal coil and a Flexigap complete the primary circuit. PVC pipe caps support the victim.

TEST 6 : Three test article with oil layer were each run in turn until failure. Input voltage and Flexigap settings were varied. In the first case the failure was near the electrolyte/oil interface, in the next two test articles failed beneath the surface. Failure typically induced by running more than 8 gap sections and/or more than 70 vac input to NST.

TEST 7 : A 2 quart polyethylene food storage bottle was run until failure, about 3 minutes under conditions above.

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