Tesla Coil Build Thread

[Sigurthr]

The air breakdown at sea level for dry (or was it 50% humid?) air between two SPHERES is 1kV/mm, but between two plates it is much higher. Between two points it is much lower. The gap being too small isn't a danger, being too large is. You start off small and expand it out wider without the primary tank connected until you get where the gap no longer reliably fires every time power is applied and interrupted. Then close it by 0.5-1mm, that's your optimal gap setting.

 

[Seoul_lasers]

i made some aluminium ones to try out, its a low power transformer so ill see how it goes

I thought copper would die easily?

here's my attempt at a static spark gap:

Hmm... you are going to loose energy with that Aluminum. Aluminum may conduct but at the temperatures that a spark gap operates at aluminium will oxidize / melt down in no time.
Copper pipe is a FAR better choice.
The adjustable spark gap below will solve many problems with spark gap adjustments. I highly recommend these for low power coils say lower than ~1.5-2Kw.

@ Sigurthr:

The air breakdown at sea level for dry (or was it 50% humid?) air between two SPHERES is 1kV/mm, but between two plates it is much higher. Between two points it is much lower. The gap being too small isn't a danger, being too large is. You start off small and expand it out wider without the primary tank connected until you get where the gap no longer reliably fires every time power is applied and interrupted. Then close it by 0.5-1mm, that's your optimal gap setting.

Exactly! Couldn't have said it better myself!
Having your gap out too far out can instantly FRY your Neon transformers or even blow caps from overcharging them.
Keep in mind that (for example) a 12KV neon will actually output closer to 17Kv if you run it without a load, this combined with a sudden discharge across a spark gap = xmfr death from winding inter-arcing. Seen this happen a few times. It isn't pretty.

As Sigurthr has pointed out, rule of thumb on a SGTC is to always set your gap smaller than you need to have the spark gap fire then work up from there until you hit the sweet spot. There is a VERY distinctive sound that a SGTC makes when it is in tune.

If you start getting popping, that's a sure sign your spark gap is set too far apart.

Here is a coil that has a slightly too large of a spark gap. Listen carefully. This is not in tune.


Here is a copper pipe gap coil in tune. Listen to the sound. Notice the tone.

 

[Speedy78]

May have to start looking around for a neon transformer and try this out after my adventure with sig's board! Would like to build a 5 foot coil including the base with all the parts. What rating should I be looking for in a neom transformer for somethibg that size? May pick one up now if yhe price is right.

 

[Fiddy]

interesting, i have copper pipe at work and solid copper machining rounds, whats the point of having heaps of pipes?

Im trying to keep the thing low profile as i can.

I will probably by these after xmas: http://www.ebay.com.au/itm/2-Pure-T...uit_Breakers_Transformers&hash=item2eb4766056

my xformer output is only 180W max

 

[Seoul_lasers]

May have to start looking around for a neon transformer and try this out after my adventure with sig's board! Would like to build a 5 foot coil including the base with all the parts. What rating should I be looking for in a neom transformer for somethibg that size? May pick one up now if yhe price is right.

For a Neon XMFR, a 12Kv 60mA both PFC/NPFC versions are fine. I prefer NPFCs as they are higher VA rating.
a 12Kv 60mA is a 720VA transformer. If you can find a 12Kv 30mA.. that's ok too. tip 2. DO NOT use electronic NSTs. These contain GFCs and are totally useless in TC applications.

Here is what you are looking for:

This is NOT what you want:

So Ideally look for anything from 10-15Kv with at least 30mA of output current. Go from there.

Look for used transformers. Should be $30-$50, no more. Ask the neon shop to "test" them for you. If you can strike an arc with it across both terminals, it's live.
Most neon shops are getting rid of the large Iron-core transformers because they are heavy and no longer to electrical safety code in many states. Also many sign shops have moved towards LEDs.
In Canada many neon shops will happily give away NSTs for a small fee as they don't want to pay for their disposal which is very expensive.
NSTs contain tar for their potting material.

 

[Sigurthr]

May have to start looking around for a neon transformer and try this out after my adventure with sig's board! Would like to build a 5 foot coil including the base with all the parts. What rating should I be looking for in a neom transformer for somethibg that size? May pick one up now if yhe price is right.

I have a matched pair of completed precision MMC and 7.5k/30ma NST I am willing to sell on the cheap. All you have to do is add a gap, primary, and secondary resonator. I can't remember the specs off the top of my head but the MMC uses 24x 942C Cornell Dubilier caps (best money can buy) which sell for over $4 each. I'll sell the pair for $75 + S&H. Let me know if you're interested.

 

[Speedy78]

Is 7.5K enough to run a 5 foot coil? I'm going to build a step up from the oneTesla with your board once all is said and done but for the SGTC I want to go all out. At least to my storage capabilities. No sense in building a coil that sits on the back patio and cant be stored in doors lol

Not having any luck on the bay with a transformer. Some nice ones listed under tesla coil transformer but of course the price is way up there.

 

[Seoul_lasers]

I have a matched pair of completed precision MMC and 7.5k/30ma NST I am willing to sell on the cheap. All you have to do is add a gap, primary, and secondary resonator. I can't remember the specs off the top of my head but the MMC uses 24x 942C Cornell Dubilier caps (best money can buy) which sell for over $4 each. I'll sell the pair for $75 + S&H. Let me know if you're interested.

That's a heck of a deal!!
Nice offer.

7.5K will be a great starter coil setup.
Desktop coil. 1ft-1.5ft discharge max.

 

[Speedy78]

See I was hoping for something larger because by the time I build that I will have a few desktop size coils already.

I assume your spec on that MMC is 0.01764uF (17.6nF) 16kV MMC (24x Cornell Dubilier 942C20S47K-F 0.047uF 2kV Polypropylene Foil Caps)

 

[Sigurthr]

Larger height doesn't translate to better output with tesla coils. My big secondary is proof of that. Stray from a good ratio of H:W too much and coil impedance soars leaving you with a very low Q factor. This makes the tuning range broad and makes it very hard to tune to optimal. If you want a lower f0 spring for a wider coil and larger Toroid, not a taller secondary.

Best I got from my tall secondary (and tall is relative; it is 18" winding of 30ga on 4.25"dia form) with the NST mmc pair was 18" streamers. The limiting factor was the secondary impedance mismatch. If I had done a 6" dia coil instead I'd have probably reached 2 foot arcs easily.

 

[Speedy78]

About how tall would it need to be at 6 inches in diameter?

 

[Seoul_lasers]

Larger height doesn't translate to better output with tesla coils. My big secondary is proof of that. Stray from a good ratio of H:W too much and coil impedance soars leaving you with a very low Q factor. This makes the tuning range broad and makes it very hard to tune to optimal. If you want a lower f0 spring for a wider coil and larger Toroid, not a taller secondary.

Best I got from my tall secondary (and tall is relative; it is 18" winding of 30ga on 4.25"dia form) with the NST mmc pair was 18" streamers. The limiting factor was the secondary impedance mismatch. If I had done a 6" dia coil instead I'd have probably reached 2 foot arcs easily.

Again.. you're dead on with this. :beer:

Too tall a coil = high resistance = lower output.
Tesla Coil secondary acts as an inductor but also has it's own capacitance value. Surface area is key. Wider coils = more energy handling capability = larger sparks.

 

[Sigurthr]

See I was hoping for something larger because by the time I build that I will have a few desktop size coils already.

I assume your spec on that MMC is 0.01764uF (17.6nF) 16kV MMC (24x Cornell Dubilier 942C20S47K-F 0.047uF 2kV Polypropylene Foil Caps)

About how tall would it need to be at 6 inches in diameter?

Hehe yup that's the specs!

That is a question for JavaTC! Aim for 125-200KHz w/ a 12x3 Toroid minimum, using 26-30ga wire.

Thanks S_L!

 

[Speedy78]

Well thats what I'm after is output and E-field for messing with the wife's cell phone screen If you really think I can get 2 foot arcs with that then I may have to take you up on that offer. There's no way I am going to find a NST and Capacitors for a MMC for that price. Provided shipping isn't 100$ lol

Got it down to 146Khz with that toroid and 28AWG. 18 inches of winding on a 6 inch diameter coil form. Just looks odd in the picture with that toroid on that thick secondary but if it performs it performs. Can't argue with performance. That is if I'm capable of not burning own the house.

 

[Seoul_lasers]

Hehe yup that's the specs!

That is a question for JavaTC! Aim for 125-200KHz w/ a 12x3 Toroid minimum, using 26-30ga wire.

Thanks S_L!

A little tip.
I would personally stay away from wire gauges any higher than 26ga as they become too easy to snap when winding. 26ga or lower should be fine. Lower Ga = larger diameter of wire.

For a 6.5" coil form, such as the one I feature in my 6.5-7Kw coil,
I used 25 ga double coated formvar magnet wire. It's good stuff. $50 for 10KG spool which is more than enough for several large coils.

My winding length was approx ~42". Just about 1750x.

 

[Speedy78]

That may make two large of a secondary for only having the 7.5Kv NSat though. I dont have any issue winding 34AWag so 28 should be a blast. If I used 25 it may be too tall and run into the issues you all were discusing earlier.