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Brand new builder in need of some info/assistance......

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Kokamo

Thu Oct 22 2009, 03:34AM

Registered Member #2442 Joined: Wed Oct 21 2009, 02:09AM
Location: Liberty Hill, Texas
Posts: 6

Herr Zapp wrote ...

Kokamo -

Since your coil IS generating at least a meager output, your NST can't be completely dead. Before assuming that a defective transformer is the root cause of your coil's poor performance, let's start to compile some specific data that will help determine what is wrong. You'r transformer could be fine, and your problems could be caused by an "out-of-tune" condition, or some other issue.

1. What is the output voltage of your NST? (your first post omitted this information)
2. What were the results of your "testing" for output (arc length) from each of the NST's two output leads?
3. Did you use any kind of Tesla coil design program to determine the physical and electrical parameters for your primary, secondary, topload, and tank capacitor? If you didn't use a TC design program, how did you determine the required values?
4. Do you know the capacitance value (either measured or calculated) of your salt-water capacitor bank?
5. What is the resonant frequency (either measured or calculated) of your Tesla coil?
6. Please provide a schematic or sketch for your coil, showing how you have everything is connected together.

So, let's start with the basics, and work through your coil's design, construction and tuning one step at a time.

Regards,
Herr Zapp

Herr, to answer your question about using software to build the coil....no, I didn't until tonight. I used TeslaMap.

For the setup's exact specs (minus electrical measurements), they are as follows....

High Voltage: Franceformer 9kv @ 30ma (again, I'm unsure it's performing properly)
Primary: #10 solid core copper wire wrapped around a 2" PVC tube exactly 15 turns tapped once per turn
Secondary: 1.300" PVC wrapped in #30 wire...exactly 6-1/2" tall at my hand count of 550 turns. (TeslaMap states differently)
Capacitor: 1 saltwater filled coke bottle wrapped in foil (not entirely sure I built it correctly) Unknown specs
Toroid: 1-1/2" aluminum duct in a small 6" circle with a crumpled ball of foil on top.

I tested the coil as per Rich's instructions and came up with a faulty NST, but like I said before, it gives off voltage and will light a neon tube, but the actual test was a bust.

After I entered as much info as I could into the TeslaMap program, I got a Resonant Frequency of 1293.7

As far as a sketch of how it is all wired up, it is all connected EXACTLY like the coil in THIS diagram.

And finally, I do not know the capacitance value of the bottle cap as I do not know how to calculate or measure it. I will study that here shortly.

I entered as much info as I know into the TeslaMap program except my bottle cap measurements because I don't know how to measure it, so I can't come up with any numbers till I get the capacitor specs.

Going to try and figure that one out.

Thanks again guys......I'm learning by the day!

~Joe
BTW...I fixed the over-sized picture problem. Hope they can be seen ok now.

Herr Zapp

Thu Oct 22 2009, 06:25AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Kokamo -

Please understand that this is not meant to be insulting, but I think there's a chance that you don't understand resonance in a Tesla coil system, or how resonance is obtained. If you didn't utilize a Tesla coil design program, did you calculate the resonant frequencies of your primary and secondary circuits "manually", using their inductance and capacitance values?

I think a good first step would be to take as much time as necessary studying Tesla coil design and theory of operation (specifically the section covering AC Spark Gap coils) at Richie Burnett's exceptional website at:

The key concept is that a Tesla coil consists of TWO "tuned" circuits: the primary circuit (consisting of the primary coil and the tank capacitor), and the secondary circuit (consisting of the secondary coil and capacitance provided by the topload). Both of these circuits possess electrical characteristics known as inductance and capacitance; the inductance and capacitance determine the frequency at which these circuits will oscillate (kind of like a bell or a tuning fork "rings" at a specific frequency, or tone).

Both of these circuits MUST be designed and constructed so they the have the same resonant frequency; you cannot achieve this resonance by chance or lucky accident, or by making the coils look "somewhat" like a picture of a Tesla coil you found somewhere on the Internet.

I'm afraid that (because it's physically so small), the resonant frequency of your secondary circuit may be so high that even a single salt-water bottle capacitor will have a capacitance value too large to bring your primary and secondary circuits into resonance. For help in calculating the value of your salt-water bottle capacitors, see the bottle capacitor calculator at:

Also, you may find the JAVATC Tesla coil design program at the same site to be more flexible and informative than Teslamap.

After you determine an approximate capacitance value for your salt-water capacitor, plug that data into your Tesla coil design program, determine the resonant frequency of the primary circuit, and see if it's anywhere near the resonant frequency of your secondary circuit.

Also, spend some time looking at the scores of different amateur-built Tesla coils on the Tesl Coil Webring; this will give you a better understanding of Tesla coil construction options.

Anyway, the most important thing is to first spend a few days (or more) studying AC Tesla coils on Richie's website. Then, you'll be able to come back to this forum with a MUCH better understanding of what you are trying to do, and be able to understand the responses and suggestions that are provided to you.

Regards,
Herr Zapp

Kokamo

Thu Oct 22 2009, 11:43AM

Registered Member #2442 Joined: Wed Oct 21 2009, 02:09AM
Location: Liberty Hill, Texas
Posts: 6

Herr, thank you so much sir. I will go do some studying on the entire concept and then come back with a few questions....or post up with results.

I appreciate your honesty, it helps more than you know,

~Joe

Renesis

Thu Oct 22 2009, 01:44PM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

If you want to learn about resonance, or anything else regarding electronics then this is a great place to start:

And of course, 4hv's HvWiki:

Those two pages, plus google, should keep you busy for a while.

If you swing a pendulum, it will oscillate at its resonant frequency. The TC's topload (toroid), the secondary coil and the earth forms a circuit with capacitance and inductance known as a LC-circuit, witch can oscillate just like the pendulum.

In the example with the pendulum it is the lengt of the pendulum that determines its resonant frequency, and with the LC-circuit it is the values of the capacitor and the inductor. Their "size" so to speak.

Lets try to swing a really heavy pendulum, a concrete slab hanging from a crane. You give it a good push, and it barely moves. But you wait for it to swing back, push it again, and this time it goes a little bit higher. You keep pushing it over and over, and soon after the slab is swinging like crasy, like a kid on a swingset.

Note this, the height of the slabs swing, its amplitude, did not affect the time it took to swing back and fourth, and neither does the weight of the slab. Only the pendulums length matters. Lets say that the slab took 5 seconds to swing back and fourth. What would happen if you pushed every 4 seconds? The slab would barely move at all. You have to match the frequency of the push to the resonant frequency of the pendulum, in this case 5 seconds or 0,2 Hertz

What you were doing to the slab is basically what the primary coil is doing to the secondary coil. When the spark gap fires a large amount of current rushes through the primary coil. This acts on the secondary coil, sending a small current upwards to the topload. The topload "capacitor" is charged, and it wants to discharge through the secondary, just like gravity wants the pendulum to come back down. When the secondary runs out of "inertia", the current begins to flow back down towards the ground. Soon the capacitor is discharged, but due to the secondary's inductance the current keeps flowing, this charges the capacitor again with a reverse voltage. Thus the current reverses again and starts to flow towards the topload, discharging the capacitor.

At this exact moment the spark gap fires again, giving the current traveling up the secondary a little push. The voltage in the topload, just like the heavy pendulum, rises to a higher level this time. This is repeated over and over, until the voltage in the topload becomes so high that it ruptures the air creating a plasma channel, a streamer. This happens hundreds of thousand times per second, way to fast for any humans to see whats going on.

As you might have understood, the primary and secondary resonance needs to be perfectly matched for this to work. The secondary's resonance is largely determined by the number of turns on the coil and the size of the topload, and it is difficult to tune accurately. So tuning a tesla coil is usually done by changing the primary's resonance, with depends on the number of turns in the coil, the value of the capacitor and the breakdown voltage of the spark gap.

I hope that made any sense to you. Im still learning too, so thats about all i can do for ya.

Did i do good Herr Zapp?

raff

Fri Oct 23 2009, 02:50PM

Registered Member #2315 Joined: Tue Aug 25 2009, 02:35AM
Location: Leyte, PH
Posts: 161

Kokamo,

I suggest you build a simple L/C meter to measure capacitance of your home made caps... google has many links... an LC meter is *BETTER* to have than guessing capacitor values...

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