Date: Mon, 28 Aug 1995 13:25:40 -0600 From: Richard Quick Subject: CAPACITOR 1/2 April 8, 1994 CAPACITR.ASC High voltage capacitor construction, by Bert Pool. First of all important warnings and disclaimers: High voltage capacitors are very dangerous for several obvious and some not-so-obvious reasons. Most experimenters know that a capacitor can retain a significant voltage even after power has been removed. Discharge all capacitors with a jumper cable before working on them. When discharging large capacitors, the jumper cable needs a high wattage 100 ohm resistor to limit discharge current. EVERY CAPACITOR IN A "SERIES" DESIGN TESLA CIRCUIT MUST BE DISCHARGED SEPARATELY! SHORTING ONE CAPACITOR WILL NOT DISCHARGE OTHER CAPACITORS IN THE CIRCUIT! Voltages and currents available on charged capacitors can be lethal. Use common sense. The capacitors described here are sealed and contain mineral oil. While mineral oil is not especially flammable, a catastrophic capacitor failure can result in pressure buildup and explosion if construction technique does not allow for release of pressure. Mineral oil will burn - a catastrophic capacitor failure can also result in the release of oil which could ignite. It is highly suggested that experimenters keep on hand a fire extinguisher rated for oil fires. Also, it is suggested that oil filled capacitor banks be stood in a metal pan large enough to contain the oil in case a capacitor container is breached or oil is released. This pan can prevent a mess, as well as help contain a potentially nasty fire! I have built over a dozen oil filled high voltage capacitors, and I have had several failures due to construction shortcuts or material failures and I have NEVER experienced a dangerous buildup of pressure or a fire - but I know it CAN happen and I take measures to be prepared for such an eventuality. Many high power Tesla coils use "power pole" transformers; these too are filled with oil and the same precautions for prevention of explosion and fire apply here too. As a high voltage experimenter, you take full responsibility for safe construction and operation of your capacitors and other high voltage devices. Be safe, be careful, use common sense! -------------------------------------------------------------------- Keeping all these safety ideas in mind, presented is a method for building home-brew polyethylene capacitors which serve very well for Tesla coils, ZPE devices, etc. The original design is not mine, it was conceived by Richard Hull of the Tesla Coil Builders of Richmond (TCBOR). TCBOR has an excellent video showing step-by-step construction of this type of capacitor. Other available video tapes provide excellent info on Tesla coil and Tesla magnifier construction. Richard Hull may be contacted at: TCBOR, 7103 Hermitage Rd, Richmond VA 23228. CAPACITOR FUNDAMENTALS: A simple capacitor consists of two conductive plates separated by an insulator. Capacitance is determined by the area of the plates, the distance between them and the "dielectric constant" of the insulator between the conducting plates. This dielectric constant is represented by a number called "K". On the next page is a table of materials and their "K" and their puncture voltages taken from the "Radio Amateurs Handbook": MATERIAL | "K" | PUNCTURE | | VOLTAGE PER | | MIL | | ============================================================= AIR 1.0 240 BAKELITE 4.4 - 5.4 300 BAKELITE, MICA FILLED 4.7 325 - 375 FORMICA 4.6 - 4.9 450 WINDOW GLASS 7.6 - 8 200 - 250 PYREX GLASS 4.8 335 MICA 5.4 3800 - 5600 PLEXIGLASS 2.8 990 POLYETHYLENE 2.3 1200 POLYSTYRENE 2.6 500 - 700 PORCELAIN 5.1 - 5.9 40 - 100 QUARTZ 3.8 1000 TEFLON 2.1 1000 - 2000 A vacuum or air has a "K" of 1. If you put a piece of teflon between your plates (same spacing), the capacitance will increase 2.1 times and it will handle at least 5 to 7 times as much voltage. If you used a piece of good quality glass, the capacitance might increase 8 times! (the voltage rating would increase only slightly). The dielectric you choose will be determined by voltage, frequency (if using a.c.), durability (glass breaks very easily), cost and physical size. MATERIALS AND SOURCES: The capacitors we will build use polyethylene. Poly is very easy to work with, does not break, is inexpensive, readily available, has very good a.c. characteristics (very low loss), and has good high voltage properties. Mica would be even better, but it is VERY expensive and is not readily available. Glass is o.k. as far as availability and cost goes, but it has very high internal losses for Tesla coil use, compared to poly. Glass is also very fragile to work with. I've made glass capacitors weighing over 600 pounds -NEVER AGAIN! You just can't beat making capacitors out of polyethylene. Purchase two sheets of polyethylene sheet, 48 inches wide by 96 inches long. Each sheet will be cut lengthwise into three sheets, each 16 inches wide. All together, you will have 6 pieces of poly 16 inches wide by 96 inches long. This is enough material to make THREE capacitors. (You will cut several more sheets if you choose to use several thin layers of plastic instead of one single thick layer.) The thickness of the poly sheets is determined by the voltage you will be placing on the capacitor. You have to take into account whether you are using d.c. or a.c. If you are using d.c. voltage, calculate your poly thickness by using dielectric voltage rating of 600 volts per mil (one mil = .001 inch). Some charts show that poly can handle 1200 volts per mil - Tesla coil experience shows that this value is NOT conservative enough, even taking peak-to-peak values into account! If you are using a.c., and especially with a Tesla coil, you have to de-rate the voltage ratings on the poly or you will have capacitor failure. For Tesla coils using input transformers from 9 kilovolts up to 15 kilovolts, use 90 mil thick polyethylene. If your input transformer is 7200 volts or less, you can use 60 mil poly. *** Special construction note! Once you have determined the required capacitor dielectric thickness, it is MUCH better to make your dielectric from several thin sheets of poly instead of one single thick sheet. Example: If you need 90 mil thick poly, use three 30 mil pieces stacked together to form a 90 mil dielectric. If you use multiple layers the insulation will be MUCH more robust than a single thick layer. The reason? If you were to use a single thick layer of poly and it had a manufacturing defect, odds are that the defect will extend all the way through the plastic. High voltage would force its way through the single defect to blow up your capacitor. If you have three or four thin layers stacked, every sheet might conceivably have a defect, BUT it would be almost impossible for all of the defects to be lined up to allow the high voltage to punch through. Odds would be that while one sheet might have a defect, you would still have several GOOD layers still providing protection. Professionally manufactured capacitors usually use this secret of layering. *** From this point on, where the text describes using "a" piece of poly, you will probably instead be substituting three or even four thin sheets of poly for the reason described above. Keep this in mind during the construction process! The capacitor described, using .0625 inch thick polyethylene will have a measured value of 0.0185 ufd with an a.c. working rating of 7500 volts r.m.s.*** A .090 inch thick polyethylene dielectric capacitor will have a value closer to 0.010 ufd, and can be used in Tesla coil circuits using a power source up to 15 kilovolts a.c. *** TCBOR suggests that .060 thick poly will work @ 15,000 volts. My experience shows this is not always true. I recommend 90 mil poly for 12,000 to 15,000 volt operation. As any coil builder knows, the resonant peak voltages go WAY above the source voltages! You must design sufficiently thick poly dielectric to handle this higher voltage. Power LOSS in one of these caps in a Tesla coil configuration is LESS than 0.5 watt per cap! Thus, they don't suffer from internal r.f. losses which translate into heat failure. A poly capacitor made with .060 poly should handle 36,000 volts d.c. and the .090 thick poly job should easily handle 54,000 volts d.c. These are very conservative ratings - good quality polyethylene might handle twice these ratings. Tesla coils, of course, use alternating current. The peak voltages generated in a resonant Tesla circuit are incredibly hard on a capacitor. This is why you must "over-engineer" the voltage capabilities of your capacitors. Capacitors may be placed in series to achieve higher voltage ratings, parallel for more capacitance. Combination series/parallel combinations may be used to achieve any desired capacitance and voltage rating. As an example, let's say you've built several 0.01 ufd capacitors rated at 7,500 volts. You make the deal of your life and acquire a terrific 15,000 volt power transformer....only your capacitors can't handle this voltage. What to do? Assuming your coil requires a capacitance of 0.01 ufd, what kind of connections can you make to use the capacitors on hand? First of all, you could connect two caps in series, as shown below: c1 c2 0.005 ufd 15 kv capacitor || || made from two 0.01 ufd, 7.5 kv ---------||----------||------ capacitors || || You now have a capacitor rated at 15,000 volts...BUT the capacitance is now only .005 ufd! You increased the voltage rating, but placing capacitors in series reduces the capacitance. Now what? We connect two more caps in series to create another 0.005 ufd capacitor, then we take our two 0.005 ufd caps and put them in PARALLEL. We end up with a 0.01 ufd capacitor rated at 15,000 volts: c1 c2 || || |-------||----||--------| 0.01 ufd, 15 kv | || || | capacitor made from --------| |--------- four 0.01 ufd, 7.5 kv | || || | capacitors |-------||----||--------| || || c3 c4 Because the transformer has an output of 15,000 volts, and we know the PEAK voltages will be much higher than this, we might wonder whether the capacitors we just wired together can handle the peak spikes. To reduce the chance of failure, we would be better off placing THREE of our capacitors in series to achieve a voltage rating of 7,500 times 3 or a total of 22,500 volts. But what would our capacitance be if we do this? Right! The capacitance will be 0.01 divided by three or 0.03333 ufd. Guess what?! We need to parallel THREE sets of these caps to bring the capacitance back up to 0.01 ufd: c1 c2 c3 || || || |-------||----||---||-----| | || || || | 0.01 ufd 22.5 kv | | capacitor made from | || || || | nine 0.01 ufd, 7.5 kv --------|-------||----||---||-----|-------- capacitors | || || || | | c4 c5 c6 | | | | || || || | |-------||----||---||-----| || || || c7 c8 c9 Using this method, you may build a capacitor rated for any capacitance and at any voltage rating! The down side is that you can use up a LOT of capacitors! We will make our conductive plates out of aluminum roof flashing. You can buy a fifty foot roll of 14 inch wide aluminum roof flashing here in the Dallas area from Home Depot for about $22 (4-93). This is almost exactly the length you will need for three caps. The aluminum flashing, by the way, is about 10 mils thick. My local Home Depot charged me - $21.80 (4-93) For a capacitor container, we use 6 inch diameter sdr 35 PVC pipe cut into 19 inch lengths. PVC pipe comes in 13 foot lengths, $1.25 per foot, or $16.25 + tax (2-93). You will also need flat "glue on" pvc end caps for this pipe; $4.40 each, or $26.40 for six (enough for 3 caps). Do NOT get the rubber gasketed end caps - they are not flat on the end and the seals will not hold up once immersed in oil. You will also need pvc primer and cement to glue the end caps to the pvc pipe. You will also need some 1/4 inch thick clear plexiglass sheet scraps, each piece large enough to cut a 6 inch diameter circle. You will need plastic tie-wrap straps about 24 inches in length, or enough 12 inch straps to link together to form nine 24 inch long straps. Try to get straps that do not contain metal teeth inside the lock of the strap. To make connection to the aluminum plates you will need some #10 screws, washers, and nuts. You will need two split-bolt electrical connectors to go on the top of each capacitor - Home Depot, $3.33 each. You will also need 3 or 4 feet of high voltage wire to connect the split-bolt output connectors to the aluminum plates. You will need two inexpensive radiator drain petcocks (valves) from Chief Auto (#852079) for $2.99 each. We will use these valves to fill the capacitor with oil and/or attach a vacuum pump. Finally, you need a very high quality mineral oil to fill the capacitor. I use SnapLube-100 from Tulco Oil in Arlington Texas, (817) 640-0051. It comes in a five gallon re-sealable pail for $43.10, including tax. I've never had an oil related capacitor failure using this oil. SnapLube 100 is a highly refined non-carcinogenic oil containig no PCB's. Stay away from PCB oils. Any way, just about any good quality, low moisture mineral oil will work in these capacitors. ACTUAL CONSTRUCTION: BOTTOM PVC end caps: Glue two 1/2 inch by 1/2 inch square pieces of plexiglass stock three inches long across the inside bottom of the BOTTOM end caps. Make sure these two strips are at least 1/4 inch away from the walls of the plastic end cap! You have to allow space for the wall of the pvc pipe to reach the bottom of the end cap. The purpose of these spacers is to prevent the rolled capacitor from sitting directly on the bottom pvc end cap. The space allows any moisture in the oil to settle to the bottom of the cap - the capacitor will sit on these plexiglass supports above the moisture contaminated oil. PVC case: Cut three pieces of 6 inch diameter pvc pipe 19 inches long. Clean the pieces with alcohol. Prime ONE end of each pipe with pvc primer. Immediately swab bunches of pvc cement on the bottom 3 inches of each pipe. Swab the inside walls of three end caps which you prepared in the first step. IMMEDIATELY push an end cap onto the glue coated end of each of the three pipes. YOU WILL NOT GLUE A CAP ONTO THE TOP OF EACH PIPE YET - JUST THE BOTTOMS! As you push the bottom end caps on, twist them to help insure a good seal. Take the remaining three end caps which will be used for the TOPS of the capacitors. Using a saber saw cut a five inch diameter hole in the end of each cap. This will leave a 1/2 inch pvc border surrounding the hole. Cut three 6 inch diameter circles out of your 1/4 thick plexiglass stock. Next, we will score the TOP of the plexiglass with a sharp metal scribe in the shape of a big X, going from edge to edge. Below is a crude picture of these two cuts. Make the scribe marks at LEAST 1/32 inch deep. /===========\ /\ \ Cut two scribe / \ / \ marks at right | \ / | angles to each | \ / | <-- TOP of plexiglass other. | / \ | capacitor cover \ / \ / \ / \/ \========/ *************** Important Safety Note ******************* The purpose of the scribe marks is to provide starting places for CRACKS to occur should the capacitor fail and excess pressure occur. The plexiglass will bow outward and crack at the scribe marks, releasing pressure. MAKE SURE THAT THE SCRIBE MARKS ARE ON TOP WHEN YOU INSTALL THIS COVER! ********************************************************* Use pvc cement and glue a 6 inch plexiglass disk over the hole you just cut in the end of the top cap. MAKE SURE THE SCRIBE MARKS ARE ON TOP! Do this for all three top end caps. You just created three TOP end caps with clear windows in the ends! *************** Safety Notes ************************* The plexiglass will seal to the pvc, but pvc cement does not effectively bond plexiglass to pvc. This is good! Should the capacitor experience a pressure buildup due to electrical failure we WANT the plexiglass to crack and come loose and let the gasses out! The plexiglass cover also allows us to SEE a capacitor failure - the light from the arc shines out! The plexiglass cover serves as at least two important safety needs! Do NOT build a capacitor without this or some other form of over- pressure release mechanism! ****************************************************** Now let all pvc cement dry for 24 hours before doing any additional work on the pipes or end caps! See "PVC CONTINUED" below for completion of the TOP end caps after the glue has dried. Aluminum: Cut your aluminum flashing into six pieces, 14 inches wide (natural width) by 93 inches long. Use large scissors to make cuts. Cut all corners round (use a fifty cent piece to mark the curves on the corners) to reduce corona. Using a hand operated paper hole punch (any office supply has these), punch a hole in ONE end of EACH sheet, about 1/2 inch from the end, midway between the end corners. Take wet/dry sandpaper and sand all burrs and rough edges off the flashing. Preparation of the aluminum edges and corners is VERY important! Any burrs or roughness will result in capacitor failure! Attach a length of high voltage wire to the hole in the aluminum using a wire terminal and # 10 hardware. The wire should be about 16 inches long. Do not do anything with the other end of the wire yet. Cut your screw off as short as possible, very close to the nut. DO NOT GET METAL FILINGS OR METAL DUST ON YOUR ALUMINUM FLASHING OR POLY! METAL DEBRIS MEANS CAPACITOR DEATH! Poly sheet: Place sheets of newspaper on a carpeted foor. Put one of your poly sheets down on the newspaper and clean both sides with paper towels and alcohol. Measure a line 16 inches from the edge. Take a magic marker and draw a line down the length of your sheet, 16 inches from the edge. Go to the opposite edge and do the same, drawing another line down the length of the sheet. Your poly sheet should now be marked into THREE equal pieces, each 16" by 96". Using a box knife, carefully cut along these lines. You will have three pieces 16" by 96" long. When you complete these two cuts, carefully set the three pieces aside on a clean piece of paper. Next, clean, mark and cut your second piece of poly stock into three pieces. It is important that the poly you use is scratch-free and umblemished! Any imperfections can cause capacitor failure. You now have six 16" by 96" pieces of poly (again, if you are layering your poly, you will have several times this number of sheets.) Assembly: Place a 16" by 96" length of poly on your newspaper. Place one of your aluminum sheets on top of this first poly sheet. Align the aluminum so that you have an even 1 inch border of poly showing all the way down it's 93 inch length. Now scoot the aluminum towards the screw end so that the aluminum hangs over the END of the poly one inch. Note the 1 inch overlap of the aluminum end over poly! | | Top |--------------------------------------| | |======================================= | | | Poly--->| | Aluminum sheet #1 O|<--hole and | | | screw for | | | wire | | | | |======================================= Left |--------------------------------------| Right Bottom Place poly sheet #2 on top of the first aluminum sheet. Align this poly exactly on top of the first poly sheet.' Place the final aluminum sheet on top of the second poly sheet. The screw end should be on the far end of the capacitor, OPPOSITE the first screw. | | Note the 1 inch overlap of the end of the aluminum over the poly! Top |--------------------------------------| |======================================= | | | |<- Poly sheet Hole & -> |O Aluminum sheet #2 | | screw | | | (poly and alum for wire | | | sheets #1 | | | omitted |======================================= | for clarity) Left |--------------------------------------| Right Bottom You should have a capacitor sandwich consisting of, from the bottom of the stack up, poly, aluminum, poly, and aluminum. Make sure that the screws on the two sheets of aluminum are NOT ON THE SAME END OF THE CAPACITOR! Now carefully roll the capacitor up, starting on the left end. Make the core hole in the center of the roll about 2 inches across. Roll the capacitor up as TIGHT as possible! KEEP THE BORDERS ON EACH SIDE OF THE ALUMINUM STRAIGHT! If your aluminum gets too close to the edge of the capacitor, high voltage can arc around the edge of the poly, causing catastrophic failure. I really suggest getting a helper to help keep things lined up straight as you roll! Once the capacitor is rolled up, you should have a cylinder 16 inches tall and about 4.5 to 5 inches in diameter. If your capacitor is much over 5 inches in diameter, then it won't fit inside the PVC pipe. Take three plastic tie-wrap straps and tie the rolled capacitor up so that it can't unroll. The two wires should come out of the top of the capacitor - one from the inside of the roll, one on the outside. Place a scrap piece of poly between the head of the screw and the underlying poly sheet so that the screw won't puncture the underlying poly sheet. PCV PREPERATION CONTINUED: Carefully slide your rolled capacitor into one of the pvc pipes, making sure the wires are "up". You should have about a 1/2 inch space between the outside of your capacitor and the inside wall of your pvc pipe. The capacitor will sit on the two plexiglass spacers which keep the capacitor 1/2 inch above the bottom of the end cap (see step one). Take two of the split-bolt connectors and set them on top of the plexiglass window on the TOP end cap. The head of the bolt will sit on top of the plexiglass. Place the two bolts opposite each other, about 5 inches apart. /===========\ Split bolt ----> / O \ / \ <-- 6 inch round cap with | | 5 inch plexi window | | | | \ / Split bolt ----> \ O / \========/ Mark the plexiglass with a marker right around the edges of the bolt where it sits on the plexiglass. Next, clamp the bolt in a vise. Drill two holes through the head of the bolts. We will use two 1.5 inch long # 10 screws through these holes to attach the bolts to the plexiglass. Take the plexiglass window and prepare to drill holes in it. Place a drilled split-bolt on the plexiglass where we marked it earlier, and mark the new hole positions on the plexi. Drill the two holes. Coat the bottom of the split bolt with epoxy and attach the split-bolt connectors to the plexiglass window with 1.5 inch # 10 hardware as shown below. The epoxy is important to prevent oil leaks. Place epoxy on the screw threads where they pass through the split bolt and where they pass through the plexiglass: || || <-- SPLIT BOLTS --> || || || || || || || === || || === || ====|==== < --- glop epoxy! -----> ====|==== =======|=========================================|======<--plexi =======|=========================================|====== glass nuts ->=== === | <-- SCREWS --> | | | Note: each split-bolt is held on with TWO sets of screws and nuts! Next, we drill and tap two holes in the plexiglass window for our two valves. Locate the holes for the valves as shown below: /===========\ Split bolt ----> / O \ / \ <-- 6 inch round cap with | | 5 inch plexi window Valve holes --->| O O | | | \ / Split bolt ----> \ O / \========/ This arrangement keeps the split-bolts far apart, and the two valves will be far enough away to prevent problems. The holes for the valves should be slightly smaller than the threaded portion of the valve. Be very careful tapping the plexiglass else it will split! Coat the threads of the threaded end of the valves with epoxy and screw the valves into the holes. The epoxy will seal the threads closed to the plexiglass and will prevent oil leaks. Do not get epoxy inside the valve itself! Give the expoy a several minutes to dry. Hold the end cap over the top of the capacitor. Test it to see how it fits down over the 6 inch pvc pipe. Make sure the screws holding the split-bolts do not come too close to the top of the capacitor. Lift the end cap off the capacitor. The wire from the inside of the capacitor will connect to a screw on one split-bolt connector; the other wire from the outside of the capacitor will connect to the OTHER split-bolt connector. Measure and cut the wires so that they are as short as possible, YET STILL LONG ENOUGH TO REACH THE SCREWS HOLDING THE SPLIT-BOLTS. Crimp and solder a round terminal connector on the end of the two capacitor wires. Attach each wire to one of the split-bolts using another couple of #10 nuts and washers. Again, temporarily slide the top end cap on and check your wires for fit. If all looks ok, it is time to glue this puppy on! First, open both vlaves so air can go through them. If you forget this step, you won't be able to push the TOP down over the pipe because of the trapped air! Slather the outside top three inches of your pvc pipe with primer. Coat the inside walls of the end cap with primer too. Next, coat over the primer with lots of pvc cement. Quickly push the cap on the pipe, twisting back and forth to make a good seal. Connect a vacuum pump to one of the valves with a length of 5/16 hose. While running the pump, apply additional glue around the lip of the cap where it touches the pipe. Listen for the hiss of air getting sucked in. If you find a leak, add pvc cement until it stops. Now is the time to find and fix any leaks! Once oil is introduced into the capacitor, leaks cannot be sealed with cement - the oil will prevent bonding! Once you are satisfied the capacitor is leak-tight, let it sit for at least 24 hours to allow the pvc cement to completely dry. DO NOT PUT OIL IN A FRESHLY GLUED PIPE, OR YOU WILL HAVE ONE HELL OF A MESS! After the glue has completely dried, test the end caps for complete seal one more time. DO NOT TEST FOR LEAKS BY PRESSURIZING THE PIPE! PRESSURIZING THE PIPE CAN RESULT IN A VERY DANGEROUS EXPLOSION SHOULD THE PLASTIC FAIL! Once you are satisfied the plastic-to-plastic seals are good we can charge the capacitor with oil. Run a 5/16 rubber hose from one valve on the cap to a vacuum pump. Pump the cap down for one hour. This will help boil out any residual moisture and will help remove air from between the layers of poly and aluminum. Once it has been pumped down, run another 5/16 inch rubber hose from the other valve down into the 5 gallon pail of oil - but do NOT open this valve yet. Turn your vacuum pump on. This will help to continue to produce a condition of reduced pressure in the capacitor. VERY slowly open the oil valve just a tiny bit. This will cause the oil to flow up the hose from the pail through the oil valve into the capacitor! WARNING: Do NOT allow oil to enter the vacuum pump or permanent damage to the pump can result! *** Be sure to slowly open the oil valve - the oil will want to foam up and enter the vacuum pump. Regulate the flow of oil so that the oil does not foam. Stop the flow of oil once the poly capacitor is under about 3/4 inch of oil. Close the oil valve completely and let the vacuum pump suck air out between the plates of the capacitor. Again, the oil will want to foam up from all the entrapped air, so you will have to monitor the vacuum valve very closely to prevent oil from foaming up and entering the vacuum pump. After a half hour or so, most of the air will be out of the capacitor - at least enough where you can open the vacuum valve so that the vacuum pump is going wide open. Be aware that you will get air bubbles coming up out of the capacitor even if you pump from now on 'til doomsday! You will actually suck air THROUGH microscopic channels in the pvc pipe and end caps! Your goal is to get as much air out of the capacitor as is practicable - usually a couple of hours of vacuum pumping will do the job. After the capacitor has been thoroughly pumped down, shut off the pump, disconnect the hoses. Slowly open one of the valves and let air into the space above the capacitor to relieve the vacuum. Close both valves on the capacitor to prevent additional air and moisture from entering the capacitor. Next comes the really hard part: set the capacitor aside for at least one week, preferrable two weeks. Two or three times a day, gently rock the capacitor from side to side. This will help air bubbles to rise. DO NOT AGITATE THE OIL! The idea to remove air bubbles, not introduce more! *********************************************************** DO NOT ATTEMPT TO USE THE CAPACITOR IMMEDIATELY AFTER PUMPING IT DOWN! If you do, entrapped air will cause it to fail. I have learned this the hard way! The capacitor needs to sit for one to two weeks to allow air to rise out of the capacitor. The number one reason for premature failure of a new capacitor is due to running the capacitor with pockets of air trapped between the layers. Failure can result from poor quality or imperfect polyethylene, insufficient poly thickness, burred aluminum edges, oil containing moisture (1 part water in 10,000 parts oil reduces the oil's insulation factor by 50% !!!) or entrapped air. Insufficient border spacing around the aluminum can also cause capacitor failure. It is highly suggested that you open one of the valves on the capacitor when using with a Tesla coil or other high peak power source in case the capacitor should fail. Having a valve open will vent a sudden build-up of pressure from the gases which come from the vaporized plastic which occurs when a capacitor fails. Close the valves whenever the cap is NOT in use to prevent moisture in the air from entering the capacitor. The capacitor should be stored and transported standing upright. If the capacitor gets turned on its side, the air in the space above the capacitor will get back into the layers of poly and aluminum - and you don't want to have to go through the pump/wait process again! Theoretically you could completely fill the capacitor with oil - providing you left a way for the oil to expand and contract with temperature changes, AND if you could build a 100% sealed PVC container. I assure you that doing this is harder than one would suspect! The pvc end caps may seep a tiny amount of oil THROUGH the plastic - pvc is not nearly as impermeable as we would be led to believe! Stand the caps upright in a large metal pan to contain any oil leakage. The pan should be large enough to contain all the oil stored in one of the capacitors. The pan will contain leakage, and should you have a capacitor container failure and oil fire, the pan will contain the burning oil - definitely a plus! Again, remember one reason why we put a clear plexiglass window on the top of the capacitor: it lets you see when you have a capacitor failure! If the capacitor fails, the high voltage arc will be visible through the clear window. If you do have a capacitor failure, DISCONNECT POWER IMMEDIATELY! FAILURE TO DISCONNECT POWER CAN RESULT IN A CATASTROPHIC CAPACITOR FAILURE! DANGERS INCLUDE EXPLOSION AND AN INTENSE OIL FIRE! ************** LEARN FROM MY MISTAKES! ****************** Due to impatience, I did not let some of my capacitors sit for a sufficient time before use, so they had air trapped in the layers. They failed. I built several capacitors with poly which was not thick enough to withstand the voltage of my transformer. They failed. In every case I quickly disconnected power. Not once have I had a "catastrophic" failure resulting in container failure or fire. But I ALWAYS keep a fire extinguisher rated for oil fires handy, just in case! So should you. ------------------------------------------------------------------- Note by Richard Quick: I have edited out a couple of paragraphs that instructed the user to burn up a couple of transformers by connecting directly to the capacitor and running about 10kV into the newly built cap! Bert indicated that the 60 cycle high voltage run into the cap would vibrate out the air bubbles. This is not correct. The caps are properly broken in by connecting to the Tesla coil and running with reduced spark gaps and reduced voltage. It is the pulse discharge of the spark gap when the tank circuit is firing that jars loose air bubbles, not a continous 60 cycle hum. Also, Bert appears a little paranoid about oil fires and explosions. My experience is that these capacitors do not get warm. I have built and operated dozens of plastic/AL/oil capacitors: I have had plenty of failures, but never had an "incident". Mineral oil has a very high flash point. It needs to smoke before it will burn. The other thing is that there is no oxidizer in the capacitor. When a failure occurs, the cap may "burp" slightly, but there is zero chance of an explosive failure.