If you are interested in making a high voltage, high current, power supply, I can tell you how to do it for free.... First call the local neon shop(s) and tell them that your working with Tesla coils. Ask them to hold all of their failed xfrmrs so you can pick them up. Make sure you talk to the boss or foreman, and tell them that you want dead units. I have never had a shop turn me down for free cores. They are happy to get rid of them. There are two types of failed neon xfrmrs: warranty units, and old junk. The local shop must return units that fail within the two year warranty period back to the distributor for credit. Old junk (older than two years) you can pick up for free right from the local shop, but I also scavenge from the distributor. Ask where the failed warranty units go. If you can locate the distributor who sells wholesale, and handles failed warranty units, you have found a gold mine of high voltage xfrmrs. The distributor removes the PLATE from the xfrmr for return to the manufacturer, and throws the unit away. The manufacturer credits the distributor for the plate, as the shipping is too expensive. The cores go to the dumpster. After locating your source of failed units, be selective. Try to bring home the high current units. Ratings commonly used are 9 kv, 12 kv, & 15 kv, with common current ratings of 30 & 60 ma. Once in awhile you will come across a 120 ma unit. I grab all of the high current units (60 ma+) I can get in these voltages. First test your units. Use wire with a 15 kv rating or better. This wire can be obtained where you pick up the transformers. If you ask they will usually cut you off a few feet for free. I prefer using the solid polyethylene core from RG-213 coax, as it will withstand the voltage with gobs of extra safety margin. Draw an arc from the HV bushing to the case, one at a time. About 50% of the "failed" units I pick up are just fine and need nothing other than a clean up. There is nothing wrong with them. Often shops get these units from signs they have dismantled, and they just toss them into the junk pile with the rest. The other 50% are bad. Either one, or both, of the HV windings have broken down. These units can frequently be repaired. Remove all hardware, and insulators if possible. Take a hammer and a chisel and remove the cases by splitting them down the corners. Break off any stubborn insulators, but try to preserve the lead wire. You are left with a block of tar. Set the unit outside when it is very cold, and let it freeze solid overnite. The next morning, short the high voltage lead wires with a clip lead, and connect 110 volts across the primary. Since the cores on these transformers are shunted, they may be shorted without harm or blowing fuses. Let the unit cook for 15-30 minutes. Disconnect your leads, and with the chisel and hammer, chip a groove around the block. You want to score a groove lengthwise that will allow the block to cleave in two. Then starting from one end of the block, chip until you hit the core, then do the same with the other end. Pry and chip the tar away from the core until the xfrmr is free. The core may then be disassembled, and the windings removed and examined. Kerosene and a stiff brush will clean up the windings and core of any remaining tar. The "cold-cook" method is fast, clean, and works very well. Since the tar is frozen it chips away cleanly. The "cooking" softens up the tar around the core allowing it to release. The only other ways I know to free the cores are long soaks in solvent such as kero or gas, (the nasty waste does make a good crack filler), or melting out the tar with external heat from a fire or oven. Most units fail when the high voltage breaks down the tar insul- ation. The resulting carbon track shorts the winding. Simply removing the tar brings them back to life. Other times the coils break down internally. In this case I discard the winding after disassembling the core, and replace it with a good winding from another unit of the same model with the same type failure. While the core is apart, you can beef up the current output by removing a few of the shunting plates between windings. Never take out more than 2 or 3 of these plates per side, as the additional power output will burn out the secondaries. Generally I get about 70-75 ma out of 60 ma units after I have finished. Rebuilt units need a little protection from the high voltage secondary outputs. The first thing I do is solder on a new lead wire to the high voltage windings. The HV secondaries are wound with very fine magnet wire, in the 30 ma units the wire is not much thicker than a coarse hair. Once a good solder connection is made, bed the connection and the first 1/2 inch or so of lead wire to the top of the HV winding with hot glue or clear epoxy. The lead wire need not be anything special, any thin insulated stranded wire may be used. Heavy wire increases the chances of a failed connection due to mechanical stress. When setting the unit up to fire you simply have to route it on insulators. The windings themselves are wedged against the core to prevent vibration. I have seen wood, bakelite, and plastic wedges used commercially. What I like to do is to soften up some 30 mil polyethylene plastic sheet in boiling water, and heat the core in a warm oven. I wrap dry softened plastic around the core and gently force the windings down on it. Once cooled, the windings have some insulation from the core, and they will not vibrate. The base wire from the HV windings must be grounded to the core. Use the original grounding point if possible, if not you may split the core apart slightly with a thin blade and insert the wire into the gap before you clamp the core back up. If required you may splice on a small piece of wire for added length. Neon sign transformers that have been rebuilt may be fired dry. The tar used to pot the cores for neon use does not really insulate well against the RF and kickback from the Tesla Tank. The units last longer when they are freed of the tar potting. The only other choice is to sink rebuilt units in mineral or xfrmr oil which is a very good RF insulator. I choose to fire them "dry"; it works, and there is no mess. Neons may be run in parallel to deliver the current required to fire medium sized coils, and I have run up to 4000 watts with banked neon power supplies. The general practice is to run these banks off of 240 volt feeds controlled through a variac. Neons with matched outputs are run in pairs in these banks. The primaries are paired up in series, and the secondaries are all paralleled to the HV buss. Phasing is important here, and each transformer must be checked as it is added to the bank to ensure it is in phase with the other units. If an xfrmr draws an arc from a lead wire brought to the HV buss, the primary or secondary connections must be reversed. Neons typically have an efficiency of about 50%, in that they draw twice as much RMS power as they put out. This problem can be resolved with the use of power factor correction (pfc) capaci- tance across the line. The pfc capacitors used are the same as for alternating current motors. The voltage rating should be at least twice the line current used, and I like a 4x voltage margin for long life. The formula used to determine ballpark pfc is as follows: 9 10^ C = Corrected kVA ------ 2 2(pi)fe^ This should read C = Corrected kVA times (10 to the ninth power) over, (2 pi times f times e squared) C = required capacitance in microfarads f = frequency of applied voltage e = applied voltage CORRECTED kVA is determined by dividing the corrected power factor output of the neon sign xfrmr (Volt-Amps below) by 1000 Corrected Power Factor Secondary Rating Volt-Amps kV,mA 15,120 900 15,60 450 15,30 250 12,120 775 12,60 400 12,30 200 9,120 600 9,60 300 9,30 150 7.5,120 500 7.5,60 250 7.5,30 125 6,60 200 6,30 100 Using a pair of rebuilt 12 kv, 60 ma neons, with 2 shunting plates removed from the core next to each HV winding, and power factor correction capacitance, you can get a nice 1.5 KVA Tesla power supply with over 90% efficiency. Total cost: $5.00 for the pfc capacitors, and a few hours of time. I have unpotted dozens of neon transformers from many different manufacturers. I have tried to make this as informative as possible, and have checked it over for mistakes. If I have erred, or was not clear on something, please let me know. Use common sense, and don't expect the first attempt to work out. On my first attempt I managed to destroy a HV winding during the unpotting, as I did not know where the windings were located on the core. But once you see one core unpotted, with minor differences, you have seen them all. ... If all else fails... Put another megavolt through it. ___ Blue Wave/QWK v2.12 >From richard.quick@slug.org Mon Dec 4 01:12 MST 1995 >Received: from uustar.starnet.net (root@uustar.starnet.net [199.217.253.12]) by uucp-1.csn.net (8.6.12/8.6.12) with SMTP id WAA24668 for ; Sun, 3 Dec 1995 22:22:29 -0700 From: richard.quick@slug.org (Richard Quick) Subject: Transformer Date: Mon, 4 Dec 1995 02:57:00 GMT To: tesla@grendel.objinc.com * Original msg to: Nussbaum@silly.com * Carbons sent to: usa-tesla@usa.net Quoting Ephraim Nussbaum ; > Well I just unpotted another transformer this one 15kv and it > seems to have the coils the way you drew, but I have another > problem. > When I first picked it up, I tested it and I got nice sparks > from one lead. When I tried the other lead I got nothing, so I > removed the cover, removed the tar on the side of that lead > until I got down to the wire that comes out of the ceramic > spacer. Where the wire is attached to the windings there was a > small copper plate with a niche in it and tar had gotten > between the plate and windings. Can I just reattach flat > against the windings (I don'tknow where it was attached). > Also there was a small wire coming out of the plate, maybe this > is what was attached to the windings. This model of transformer uses a small metal plate as a connector between the winding and the lead wires. I have also seen HV windings on neons that used the same connector system to the core at the other end. > I, through cleaning, tore a few of the windings (5 or 6) does > it matter? I held the plate against the windings with an > insulated screwdriver and then tested to see if I would sparks > off the lead and I still didn't get anything. Any help would be > appreciated. It sounds as if the winding is broken down. You are obviously experienced enough to know that the HV windings are very delicate. The wire is not much thicker than a coarse hair. In order to salvage the winding (if it indeed can be salvaged) you need to isolate the end of the winding, clean the wire very carefully, and imbed the last 1/4 inch or so in a nice solder connection to a new lead wire. If the connection is electrically poor or intermittant the resistance will cause the end of the winding to heat up and melt, opening the circuit again. Losing a few turns at the end of the winding will not really affect things, as long as the end of the winding can be located and a decent connection to it can be made. The real problem occurs when a winding has failed internally. The wire, being so delicate, can easily short or burn due to a defect in the materials or the construction. If you are not able to coax any output from a winding after ensuring a decent electrical connection at both ends, pitch it without a second thought. I hang onto the cores and all good windings until I can swap in a winding from another transformer with the same type failure. Richard Quick >From richard.quick@slug.org Sat Dec 2 01:17 MST 1995 >Received: from uustar.starnet.net (root@uustar.starnet.net [199.217.253.12]) by uucp-1.csn.net (8.6.12/8.6.12) with SMTP id SAA06906 for ; Fri, 1 Dec 1995 18:12:53 -0700 From: richard.quick@slug.org (Richard Quick) Subject: NEON TRANSFORMERS Date: Fri, 1 Dec 1995 23:43:00 GMT To: tesla@grendel.objinc.com Quoting ed@alumni.caltech.edu (Edward V. Phillips): Ed> Richard: > As comprehensive as your writings on neon sign transformers > have been, there are some points you have either not covered > or which I have missed. A number of years ago my carpool > buddy and I were driving home from work and noticed several > neon sign transformers lying in the iceplant next to a > freeway on ramp. We came back to investigate and found a > half dozen FRANCEFORMER 12 kV, 60 ma power factor corrected > transformers, which we split down the middle. There was > also a 9 kV, 60 ma transformer which I got. To make a long > story short, all of these transformers, which had obviously > fallen off the back of a truck as it went round a curve, had > more or less damage to the insulators. I have been able to > use two of my 12 kV transformers, but am now interested in > rehabilitating the third, if possible. Here is the problem: > One insulator is completely broken and gone, together with > the stud which ran through it. When I look into the empty > hole I see tar with no wire visible. Questions: > 1. Is it likely that when the stud broke off it pulled the > attached lead out of the transformer so that winding is now > NG? It is very unlikely the windings are damaged or destroyed. This same thing frequently happens in the course of a normal un- potting. With a little bit of experience in unpotting a particular make and model of transformer, the builder learns the location and orientation of the spring steel retaining clip used to hold the HV bushing (or insulator) in place. With this knowledge it is fairly easy to dig a small hole in the asphalt with a screwdriver, pop the retaining clip out of the potting, and remove the insulator without damaging the porcelain or the lead wire. Without this key little bit of knowledge, the builder usually ends up cracking the insulators off with a hammer, and the thin HV lead wire is frequently cut, sheared, or pulled out of the potting. All is not lost, in fact the setback is minor. > 2. If there is hope of salvaging the transformer, I am left > with the alternative of peeling off the case, as you recommend, > or attempting to melt out the tar so that I can at least get > access to the winding whose lead no longer gets through to the > outside world. I kind of favor melting out the tar, as I would > like to reuse the case. Questions with regard to that are: > 3. What is wrong with melting out the tar? In some ways it is > less messy than chiseling off the case and the tar. As you already suspect there is more than one way to "skin this cat". Regardless of the particular method actually used to physically remove the asphalt potting (it is not really tar), I still advise removal of the case before doing anything. Melting out the asphalt potting without removal of the case means removal of the lid and placing the case either on it's side or in an inverted position in a pan, on a rack, etc., while heating. When the asphalt begins to flow out of the case it exposes the delicate windings, then the entire core will suddenly drop out or roll sideways in the case and damage the exposed windings. On the other hand, you can split the corners of the case clean down with a hammer and chisel, beat the asphalt block with a small sledge even if you desire, and the windings are safely protected by the potting. Once the block is freed it may be placed in a pan and heated, and the block will settle gently on the windings where they will not be damaged. > 4. Are the windings attached to the case, or is the transformer > just sitting in the tar? The entire core is really just sitting on the bottom of the case. There is a small steel strap which electrically connects the core to the case at the same location where the grounding lug is screwed in. Once the grounding lug is removed the only physical connection that exists between the core and the case is through the lead wires. Once the potting is removed, the case is just useless junk. It serves no purpose other than to hold the potting. > I am thinking of putting the whole thing in an oven I have, > and letting the tar melt into a pan. If this resulted in the > transformer falling out of the case and ripping off the > remaining leads the whole operation would be a big and very > messy waste of time. > Any comments or suggestions? Go ahead and bust the insulators to dust with a hammer, then chisel the case off by splitting the welds/corners from the top down to the base. If the asphalt block still does not come free then pry the base of the case away with a hammer and screwdriver. Don't spare the force and damn the lead wires. Just watch the fingers and hands, I have gashed myself more than once doing this. Heavy gloves would be advisable. Someone mentioned using a cutting wheel on a dremmel tool, I have used air chisels, whatever works. Toss the block into a pan and heat at 375 - 400 degrees until the asphalt begins to soften and run (about 30-40 minutes), then reduce the temp below 300 or so and cook carefully until done. There are spliced connections where the windings are wired to the lead wires. These splices are well protected as they are located deep in the potting. Once the core is freed from the potting the old lead wires can be easily replaced. The reason I am not really enthusiastic about melting the asphalt out is that the melting temperature of the potting and the smoking/burning temperature of the transformer fall in a very narrow range. The temperature range varies from core to core depending on the age and quality of that particular potting. Some cores with nylon wedges pinning the windings in place can become a molten plastic mess if the nylon melts, mixes with asphalt, then later cools on the sides of the HV windings. The clean-up requires hours with a dental pick. By far the cleanest and simplest way to unpott cores bedded in asphalt is to soak the core (sans case) in a medium sized (not kitchen size) rectanglar household polyethylene trash can. One gallon of diesel, kero, or gas will remove all the potting in two - three days if the solvent is kept between 40 - 50 degrees in a garage or outside porch. The unpotted core is then split, the windings removed, and everthing can be finished up with a few minutes of scrubbing with an old toothbrush and a cup of clean solvent. The waste can be then be poured into a couple of one gallon plastic milk containers which will hold up long enough to take it to the gas station, oil change station, muni recycling center etc., where it can be safely disposed of in the waste oil sump. The windings will dry thoroughly after about a 7 - 10 days laying out on some clean newspaper. Turn them every day or two. Richard Quick On Wed, 6 Dec 1995 tesla@grendel.objinc.com wrote: > I recently unpacked a Transco neon sign transformer (15 kv, 30 ma) to > find that there was no tar in it. It is instead filled with some sort of > plastic/resin. This stuff is extremely hard and I have had little luck The white/cream stuff? I _hate_ it when they do that! > with a hack saw. Anybody know how to get rid of this stuff? I had pretty good luck with freezing it and chipping it away, pretty much the way you would do a regular tar potted xfrmr, but a little more elbow grease needed. The one that I did had this convenient sleeving over the windings to make the job easier. Stan Harle Alamogordo, NM > I recently unpacked a Transco neon sign transformer (15 kv, 30 ma) to > find that there was no tar in it. It is instead filled with some sort > of plastic/resin. This stuff is extremely hard and I have had little > luck with a hack saw. Anybody know how to get rid of this stuff? There is a new type of neon potting that has emerged recently. This new potting is a cream colored opaque polymer of some type. It is not affected by the solvents normally used to unpot neon cores. It is recommended that this material be removed by the "cold-cook" method. Freezing makes the material very brittle and it will chip away easily, the warm core will allow the polymer to release from the windings without too much difficulty. Richard Quick ... If all else fails... Throw another megavolt across it! ___ Blue Wave/QWK v2.12 Hi All, Well its the begining of a new year and pretty much snowed in, so decided to unpot some transformers I had collected over the past year. Upon doing so I ran into some rather interesting designs, thought I would share with any who were interested. Here it goes... ------------------------------------------------------------------------------- First of all when I unpot transformers, like RQ, I do 3 or more at a time. I also have a tendency of doing all the transformers from a particular manufactorer at the same time. Well this time I have 7 transformers of the 30mA range from Jefferson Electric (MagneTek). There are rated as follows: (i) 5000V@30mA (ii) 6000V@30mA (iii) 7500V@30mA (iv) 9000V@30mA (v) 12000V@30mA (vi) 12000V@30mA I unpotted the above transformers using RQ's cold-cook method, I then cleaned the core and windings as best as possible with kerosene. Then I proceeded to disassemble the core and windings, PROBLEM. The problem is that in all the transformers, with the exception of the 9000V@30mA, the core had no bolts, rivets, or pins holding it together. Also I noticed it had the abnormal configuration, which I had before in other transformers: +------------------------------------------------------------------------+ | | | +--------------------------------------------------------------------|* | | | | | | | | | | | | *|--------------------------------------------------------------------+ | | | *|--------------------------------------------------------------------+ | | | | | | | | | | | | | | +--------------------------------------------------------------------|* | | +------------------------------------------------------------------------+ Figure 1: Stamped Core -------- +-------------------------------------------------------------------------+ | | | +-------------|---|-----------------------|---------------------------|* | | |///| | | | | | |///| | | | | | |///| | | | *|---| |///| | | | | | P1 |///| S1 | S2 | | *|---| |///| | | | | | |///| | | | | | |///| | | | | | |///| | | | | +-------------|---|-----------------------|---------------------------|* | | +-------------------------------------------------------------------------+ Figure 2: Core shown with Windings --------- P1: Primary Winding (input) S1: Secondary Winding 1 (output) S2: Secondary Winding 2 (output) NOTE: The area between P1 and S1 (///) are the shunts, which can be removed to increase current, but REMOVE NO MORE THAN 2, otherwise the TRANSFORMER WILL BURN UP, I say this from experience... In both figures above there are "*"'s at certain points on side of the core. These are the problem. They are what holds this 3 piece core together. At first I thought maybe it was a high temp solder, wishful thinking, but instead it is a strip-weld. I contacted Jefferson Electric in New York and talked to one of the guys there and he confirmed this. Now I use three means to remove these strip-weld(s): (1) If you have some type of welder, then just unweld it (SOME WHAT EASY) (2) Another way is to cut through the strip-weld with a hack-saw (EASIER SAID THEN DONE) (3) My perferred method is using a Dremel Tool with a metal cutting/grinding tool on it, cuts through it like hot butter (SIMPLE) Now you can take the core apart, in 3 peices, and remove the windings. IMPORTANT NOTE, WITH MOST TRANSFORMERS OF THE ABOVE CONFIGURATION (both secondary windings on the same side of the primary) IT IS IMPORTANT TO MAKE SURE THE WINDINGS GO BACK ON THE SAME WAY YOU TOOK THEM OFF. (the transformer may not work properly otherwise and might burn up)...also from experience. I usually remove the windings from the core, use kerosene to remove the remainder of the potting compound, and then let dry for a few days. Then I rebuild/rewire the windings and recondition the core if necessary (as to RQ spec's). Now they are ready to go back together. But how will you reconnect the core??? +-----------------------------------------------------------+ | | | +-------------------------------------------------------+ +---+ | | | | | | | | +---+ +---+---------------------------------------------------+ | | | +---+ +---+---------------------------------------------------+ | | | | | | | | | | +-------------------------------------------------------+ +---+ | | +-----------------------------------------------------------+ left right Top View -------- Welding this back together would be the best thing to do, but I frequently disassemble the transformers and it becomes quite bothersome, plus most people don't have access to a welder... I have used several methods to fasten the core assembly back together, but the most reliable I have found so far is as follows: (1) Find a material suitable a as support. I generally use very thin plexi-glass (1/16") or aluminum flashing wrapped in electrical tape. Plexi-glass is generally better if you have it. (2) Cut the material for the supports. You will need 3 for the top and 3 for the bottom. My design is usually like this: +---+ +---+ | o | | o | | | | | | | | o | | o | +---+ | | | | Brace B | o | +---+ Brace A You will need 2 of Brace A type and 4 of Brace B type. NOTE: Brace A should be as long as the core is wide (NOT THICK!!) (3) Next you need to find bolts that will be long enough to go throught the core yet are relativily small in diameter, you don't want to drill a large hole in the core. After you have 6 bolts w/nuts and washers select the proper sized drill bit and get ready to drill holes in the core. I use long skinny bolts (5"L x 1/16"D) that I get at a local motor repair shop but I think (not sure) that Home Depot carries them as well. You don't need the bolts that long, I use them that long because when I am finished connecting everthing back together, assuming everthing is still uniform, the longer bolts create a nice little stand to support the transformer, and with a little work you can secure it to just about anything. (4) Drilling is the hard part, unless you have a drill press. Support Brace A is for the top & bottom of the core's left side (as labeled in the above core diagram) and Support Brace B is for the top & bottom of the core's right side corners. It should be fairly obvious where they go. If you luck out and do it correctly you only have to drill 3 holes because there are usually holes drilled in all 4 corners (but not always). All the drilling is usually done on the center or T-shaped core piece. Place the core together (WITHOUT THE WINDINGS, MIGHT DAMAGE THEM WHEN DRILLING!!!) and mark where the Support Braces go and where the holes need to be drilled. Take it apart and drill the holes. NOTE: If the core on your transformer has the 4 pre-drilled holes in the corners already, by all means use them (its alot less less work). Remember though, those holes are generally going to be alot bigger in diameter than the holes you will drill so do not use the small diameter bolts. I suggest finding a bolt with the exact (or as close as possible) diameter as the hole, if you use the smaller diameter bolts, the stability is decreased dramatically. (5) Reassemble the core and the windings, attach the Support Braces, tighten the bolts and thats it, the transformer is back together. Make sure you check the windings and make sure they are not lose otherwise they may raddle when the transformer is in use. Although this procedure is not exactly easy and alittle time consuming, it is for the most part worth it, the transformer last longer and operates better when reconditioned and set up to fire-dry. I don't have as much experience and time in reconditioning neon transformers as most on this listserv do but I thought I would share my method with everyone. If any one has a better method of doing any of the above, by all means please let me know. I am getting ready to start unpotting my Jefferson Electric (MagneTek) 60mA and 120mA next, then I will move onto the FRACEformers, if I notice any differences or experience any problems I will do another write up on it, assuming I can find a solution to the problem...:)! Happy Coiling, Tim