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Registered Member #2416
Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91
Hello, I bought this NST from my local neon sign shop a few years back and he told me that it was a 9/60 but I've never been sure. It looks like a 9/60 but I'm confused by what the label says. I've tried to make a TC with it but with poor results and I was thinking my primary cap bank wasn't tailored to this transformer because it might not be a 9/60. I have pretty good experience with high voltage and I've built a few TCs that work great but this NST is weird Can you guys explain what all these specs mean?
Is it a 9/30 by the short circuit current? The wattage divided by 9kv is 15mA, is it a 9/15? What does the 2.0 A mean?
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Xplorer =
Exactly as the nameplate states, the maximum output current, into a dead short, is 30ma. The maximum open-circuit output voltage is 9kV.
For a Tesla coil using a static spark gap , the proper tank capacitor value for this transformer will be around .014uF.
First thing to do is to verify that each secondary is delivering ~4500V relative to the case ground. If you don't have a high-voltage probe, a crude test can be performed by connecting a short piece of stiff wire to each HV bushing, and positioning the free ends of the wires about 1/8" from the metal case. Apply power, and verify that both wires generate a nice fat, blue arc. Turn off the power, increase the gap at each wire by about 1/8", and test again. Repeat until you've found the maximum arc length. The maximum arc length that can be delivered from each bushing should be approximately the same length. Any distinct difference in arc length indicates a defective transformer.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Hello there Tony!
A lot of practical experiments have shown that the voltage will really start to fall long before your 30mA max is reached. I'd think of your 9000V as being the maximum unloaded RMS voltage (i.e. 12.6kV peak). Once you start to pull current, the voltage will start to fall fairly quickly until your 30mA short circuit current is reached.
So far as I understand it, for American NSTs, the typical transformer secondary operating current is approximately 80 percent of the rated short circuit current. For a transformer rated at 30 mA like yours, this would be about 24 mA. With European transformers, the G-factor as it is called - the ratio of loaded to unloaded voltage is but 2:1, meaning the voltage of a 30mA rated European NST will start to fall after just 15mA.
You have chosen the right sort of NST - - the old type with an iron core - which are the ones we need for Tesla work, rather than the modern electronic type, which are no good to us.
An NST is a special sort of transformer, where magnetic shunts (pieces of iron) in the core, automatically limit the current that can be drawn from the transformer for safety's sake. Even so, an NST can kill, son, and once you have a beefy capacitor charged up to your peak 12.6kV, you will very likely be immediately transported to the Great Beyond if you make a mistake, so please do take the very greatest care with your experiments! We all want you to become a regular member!
Please do ask as many questions as you need to ask, so long as you've checked first to make sure the answer isn't easily available to you on the web in a way that you can understand - a kind of laziness we don't like here because it takes time to give carefully considered answers to questions, and this is a site with high expectations of its members!
You've got your first NST, your entry card, so welcome to the strangely beautiful world of high voltage, Paul!
Registered Member #2416
Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91
Harry wrote ...
Hello there Tony!
A lot of practical experiments have shown that the voltage will really start to fall long before your 30mA max is reached. I'd think of your 9000V as being the maximum unloaded RMS voltage (i.e. 12.6kV peak). Once you start to pull current, the voltage will start to fall fairly quickly until your 30mA short circuit current is reached.
So far as I understand it, for American NSTs, the typical transformer secondary operating current is approximately 80 percent of the rated short circuit current. For a transformer rated at 30 mA like yours, this would be about 24 mA. With European transformers, the G-factor as it is called - the ratio of loaded to unloaded voltage is but 2:1, meaning the voltage of a 30mA rated European NST will start to fall after just 15mA.
You have chosen the right sort of NST - - the old type with an iron core - which are the ones we need for Tesla work, rather than the modern electronic type, which are no good to us.
An NST is a special sort of transformer, where magnetic shunts (pieces of iron) in the core, automatically limit the current that can be drawn from the transformer for safety's sake. Even so, an NST can kill, son, and once you have a beefy capacitor charged up to your peak 12.6kV, you will very likely be immediately transported to the Great Beyond if you make a mistake, so please do take the very greatest care with your experiments! We all want you to become a regular member!
Please do ask as many questions as you need to ask, so long as you've checked first to make sure the answer isn't easily available to you on the web in a way that you can understand - a kind of laziness we don't like here because it takes time to give carefully considered answers to questions, and this is a site with high expectations of its members!
You've got your first NST, your entry card, so welcome to the strangely beautiful world of high voltage, Paul!
Harry.
Thank you very much for that Paul.
I have been playing around with high voltage for some time and I am very careful. This wouldn't be my first actually. I've made one before with a 12/60 NST and it works great, no problems at all considering it's about as simple as they get. Even though it works great I only have a basic idea about how they work. : )
But this TC is going to be my mini Tesla Coil. This NST is made in Japan so what current should I use to figure out the parameters of the capacitor? Will these capacitors do? They're really cheap so I hope so.
If I have 2 strings of 15 that will give me a capacitance of .0133uF at a max voltage of 9450v.
Here is a picture of my completed coils I hope the aspect ratio isn't to big at 7.3:1.
And here is a picture of my first TC. I'm getting about 30in streamers.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Hey Tony, I'm Harry, not Paul! ("Old Harry" is an ancient English name for The Devil! )
Sorry if I got you wrong about being a total beginner - I guess I just assumed it from the very basic nature of your query about the NST. (Nice work on your first TC by the way.)
The 2A means that the nominal AC mains input is 2 amperes.
Some of our members have forgotten more about TCs than I ever knew, so I'll leave it to them to take up your queries about aspect ratio and so on.
Back to your NST, Tony, whilst it was made in Japan, it was made for the American market, as the ID plate makes clear, so for want of better info, I'd assume it was made to US NST standards i.e. where the G-factor is 1.25:1 (i.e. 80% of the nominal 30mA before severe voltage fall off) rather than the European standard of G = 2:1, where the voltage starts to fall at only half the rated short-circuit current. (which would be 15mA for your transformer)
Anyway, Tony, this is all a bit academic, because that is the transformer you have got, and you must make of it the best as you can what ever its G-spot/factor!
What I do know from watching the succeses and failures of my TC inclined pals here over the last few years, is that blind optimism very often leads folk to make coils far too big for their means of driving them - everyone wants a great phallic tower of sparks - but you'll do better (IMHO) if you think very conservatively, and build a coil for which your NST is more than adequate, so you have something which works well every time you switch it on, and avoid disappointment.
If you feel you need to know more about measuring the current of your NST under varying loads, do please let me know. Either I, or one of our more experienced members, (I have always been and will always remain a beginner till Schroedinger's Cat decomposes in its mysterious box!) will be able to help you perform the necessary tests if you have the necessary basic measuring instruments - something very often overlooked in the rush to get into the hobby!
So far as I am concerned, measurement is at the heart of all that is done here that is done well, (what keeps us apart from all the DIY pseudo-scientists whose sickly websites proliferate across the web) and I would go so far as to say that measurement was the very soul of science itself.
So don't guess, Tony, or ask for someone else's guess - get out and measure it!
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Xxplorer -
Sorry, your "cheap" surplus capacitors are totally unsuitable for use in a Tesla coil MMC.
The dielectric material is Mylar, a trade name for polyester. Polyester das a very high dissipation factor at high frequencies, and these capacitors will quickly overheat and fail in a small Tesla coil system.
The transformer/capacitor matching recommendations on Deep Fried Neon are "incorrect" in that they show the "resonant" capacitor value. Using a resonant capacitor value in a Tesla coil tank circuit can allow extremely high voltages to develop that can destroy both the NST and the tank capacitor. (See the section on AC resonant charging on Richie Burnett's website at:
What you really want is a "larger than resonant" (LTR) capacitor value that won't be subject to the resonant rise problems. See a more comprehensive transformer-capacitor matching chart (MMC Cap Chart) at: Remember that this chart is specifically designed around the C-D 942C series, .15uF @ 2kV capacitor.
You will need to select capacitors that have a low-loss dielectric, like mica or polypropylene, and that are rated for high-frequency and high pulse current. One of the best types, well proven in Tesla coil systems, are the Cornell-Dubilier 942C series. A frequently-used part is the .15uF, 2kV model. You should expect to pay around $3.50 each for these capacitors, either ordered directly from a C-D distributor, purchased on eBay, etc.
You also need to boost your total MMC voltage rating considerably to get a reliable system. Your NST has a RMS output voltage of 9kV. The peak output voltage is 9,000 X 1.414, or close to 12,750 volts. Your capacitor should have a DC rating of at least 2.5X the peak voltage, or around 32kV.
The transformer-capacitor matching chart at Classic Tesla will show you two options for a LTR, static-gap system: 1. A single string of 11 capacitors in series, with a moderate reliability factor; 2. Two parallel strings of 11 capacitors (22 capacitors total), with a fairly high reliability factor.
Don't worry about your secondary aspect ratio, as long as you design-in an appropriate primary-secondary coupling factor. Use the JAVATC design calculator at ClassicTesla.com to design your coil, and determine how to achieve an appropriate coupling factor.
Registered Member #2416
Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91
Hey guys I have another question. What is coupling and the coupling coefficent? I'm sorry if this is trivial. I know it has something to do with the physical set up of the primary and secondary. I've read that the best way to go about dialing in the coupling is to over couple the primary and then slowly lower it until you achieve max performance and to use proper isolation between the two coils.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Xplorer -
Understanding primary-secondary coupling (k factor) is a pretty important part of understanding how Tesla coils work, how to tune them, and how to obtain best performance. Coupling affects many aspects of a coil's operation.
Probably the best source for information is Richie Burnett's exceptional website at:http://www.richieburnett.co.uk/tesla.shtml
The section dealing with coupling is at:
If you don't know what coupling is, you may also need to review the all the sections on Richie's site that deal with AC spark-gap coils: the component analysis, operating characteristics including ringup, quenching, AC resonant charging, static spark gap analysis, etc. Understanding all this stuff is essential if you really want to know how a coil operates, and how to tune a coil for best performance. There's a lot of information here, and it may take several days of reading to really grasp all the concepts.
Generally speaking, for a basic AC spark gap coil you will want to design your primary and secondary dimensions to obtain a coupling factor of between ~.12 and .16. The JAVATC design program (classictesla.com) will help you determine the dimensions that will yield k factors in this range. Also, it's a good idea to incorporate some means of raising or lowering the secondary through a range of +/- an inch or so of nominal position to allow adjustment of coupling.
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Can you tell me how many mA this NST is?
) 
(Nice work on your first TC by the way.)