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Neon sign transformers for Tesla coil

billybob

Member
Also I’m building the cap bank today after school. I bought 7 glass picture frames about a foot long and 8 inches large. Hoping I can rig something that will last at least a few months hopefully longer but I don’t know how reliable homemade glass caps are.
 

DerStrom8

Super Moderator
Most Helpful Member
I recommend the following link for a number of calculators to help you on your way:

http://deepfriedneon.com/tesla_frame6.html

Start by determining the required MMC capacitance to match your transformer(s) with the "Capacitor to Transformer Match" calculator. Then use the "Plate Capacitor" calculator to determine how many of your homemade glass caps would be required to meet those requirements.
 

DerStrom8

Super Moderator
Most Helpful Member
Thank you all for the advice. I heard however that it is a bad idea to phase OBITs because the secondary resistance is so high is this true? And if it is how can I go around that without damaging my transformers
I'm afraid I can't speak to this as I have never paralleled OBITs. Off the top of my head I'm not sure why this would be an issue, but could you cite your source?
 

shortbus=

Well-Known Member
Most Helpful Member
I'm afraid I can't speak to this as I have never paralleled OBITs. Off the top of my head I'm not sure why this would be an issue,
Matt, wouldn't this be like any other transformers? By that I mean that the windings must be in phase. Picking random non similar manufacturers transformers you would/could have a coin toss situation as to phase of the windings.
 

billybob

Member
Matt, wouldn't this be like any other transformers? By that I mean that the windings must be in phase. Picking random non similar manufacturers transformers you would/could have a coin toss situation as to phase of the windings.
I was thinking the same thing, unfortunately I couldn't find the source of phasing OBITs saying it was a bad idea. I just thought that the secondary couldn't handle the current when in phase. As you said though they should be like every other power transformer. I'm just taking the safe route right now because I don't have the money to replace a transformer at the moment.
 

billybob

Member
Also I finished winding the secondary today, got about 875 turns 25 inches 24 gauge. Right now I'm just coating the heck out of it with polyurethane varnish layer after layer. I got tired waiting for a spindle to be built so I spent around 2 or 3 solid hours winding by hand with a little contraption made out of legos.
Didn't take as much time as I thought it would so that was a plus.
 

DerStrom8

Super Moderator
Most Helpful Member
Matt, wouldn't this be like any other transformers? By that I mean that the windings must be in phase. Picking random non similar manufacturers transformers you would/could have a coin toss situation as to phase of the windings.
I may have misunderstood. The process of phasing could be problematic if they're put in the wrong phase at any point, yes. It wouldn't be due to high resistance of the windings though, it would be due to breakdown of the insulation.
 

shortbus=

Well-Known Member
Most Helpful Member
Also I finished winding the secondary today, got about 875 turns 25 inches 24 gauge.
Been a long time since I messed with this stuff, so I may be wrong with how people do it today. But back in the day they wound the secondary with a piece of twine between the wire, to keep a space between the wraps. It was quite a pain to do but was needed(supposedly) to keep the vvoltage from jumping over. But then again back then magnet wire wasn't as well insulated back then. The whole secondary, wire and twine was then varnished with many coats.
 

billybob

Member
Been a long time since I messed with this stuff, so I may be wrong with how people do it today. But back in the day they wound the secondary with a piece of twine between the wire, to keep a space between the wraps. It was quite a pain to do but was needed(supposedly) to keep the voltage from jumping over. But then again back then magnet wire wasn't as well insulated back then. The whole secondary, wire and twine was then varnished with many coats.
I've heard of people doing that before, but I also know it works without so I didn't do it. I'm sure it will help with the arcing problem, but to get the ratio right it needed to be around 24 inches high with a 4 inch diameter around 800-1000 turns. The gaps in between would make it more compicated.
 

gary350

Well-Known Member
When I was on the other Tesla Forum about 1995 several people did enough research to learn what worked best. 950 turn secondary coil was always best for all secondary coils. Diameter to length ratio 5 to 1 was best for secondary coil. Flat wound primary coil is best with a strike rail. Richard Hall figured out capacitor voltage rating should be 3 times more than the power supply voltage. HV transformer needs choke coils to keep RF out of the transformer. I forgot how to determine capacitor value? I invented the variable speed vacuum fan RQ spark gap it works much better than a rotor, very easy to build, and you can dial in the spark gap frequency to match the tesla coil resonance frequency for maximum spark length. Several people tried my spark gap and said it is much better than a rotor but it never caught on with the whole group. People thought the rotor looks so cool it has to be good. LOL. Been there done that. I sold all 7 of my TCs 20 years ago.
 

billybob

Member
When I was on the other Tesla Forum about 1995 several people did enough research to learn what worked best. 950 turn secondary coil was always best for all secondary coils. Diameter to length ratio 5 to 1 was best for secondary coil. Flat wound primary coil is best with a strike rail. Richard Hall figured out capacitor voltage rating should be 3 times more than the power supply voltage. HV transformer needs choke coils to keep RF out of the transformer. I forgot how to determine capacitor value? I invented the variable speed vacuum fan RQ spark gap it works much better than a rotor, very easy to build, and you can dial in the spark gap frequency to match the tesla coil resonance frequency for maximum spark length. Several people tried my spark gap and said it is much better than a rotor but it never caught on with the whole group. People thought the rotor looks so cool it has to be good. LOL. Been there done that. I sold all 7 of my TCs 20 years ago.
Yes I did your spark gap design, I'm excited to see how that goes. Need to find a variable dc source 0-12 volts around 4-5 amps to power the vacuum fan and adjust it.
 
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billybob

Member
I was wondering, should I include a Terry filter to the tesla coil? It says here that it is not necessary, but I want to protect the OBITs somehow. Whether it's just a few choke coils I don't care.
 

gary350

Well-Known Member
I was wondering, should I include a Terry filter to the tesla coil? It says here that it is not necessary, but I want to protect the OBITs somehow. Whether it's just a few choke coils I don't care.
Any protection device that works and protects the transformer is good. I have very good luck with 30 tunes of #14 solid copper insulated house wire on a 2" diameter choke toroid. I use a 120vac variac for speed control for the AC motor spark gap fan. I use fans from a vacuum cleaner. I did experiments with secondary coils in parallel 2 & 3 coils wound over the top of each other soldered in parallel. I tested a 950 turn secondary spark output was 20" long, same 950 turn secondary with 2 coils 950 turns each wound over top each other produced 21" long sparks, and 3 coils wound over each other produced 22" long sparks. Multi secondary coils are not a big improvement but it works. I always thought it would be cool to find a way to discharge my big capacitor bank though a 12 ft long TC spark. I have 3 caps in parallel rated 5000VDC 18,000. amps each = 270,000,000. watts. The cap bank is amazing to play with they will vaporize 6 ft of 1/8" diameter steel wire the BOOM is as loud as a high powered rifle. I use to discharge the cap bank over and over on 4th of July police would come to see if I was shoot illegal M-80 firecrackers. LOL. I got several free used airport runway lights once I discharged my 270KW cap bank through the bulbs they made 1 BIG flash and a BIG explosions, and totally vaporized each light bulbs, the metal base & glass were gone.

PS-1_zps916f8803.jpg
 

DerStrom8

Super Moderator
Most Helpful Member
I was wondering, should I include a Terry filter to the tesla coil? It says here that it is not necessary, but I want to protect the OBITs somehow. Whether it's just a few choke coils I don't care.
Filters may not be required but they are strongly recommended. The resonant primary circuit causes very large high-voltage and high-frequency transients which can damage the transformers especially with long-term use. Simple chokes will help block the high frequency from being fed back into the transformer, and a Terry filter is the cat's meow when it comes to filtering.
 

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