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First Tesla Coil - problems getting streamers

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void109

Tue Jul 20 2010, 02:06AM

Registered Member #3016 Joined: Tue Jul 20 2010, 01:55AM
Location:
Posts: 9

Let me run down my setup, and maybe someone can tell me where to look for issues.

Primary Circuit:
Variac ->
Line Filter ->
70 uF PFC cap ->
9kV 30mA NST ->
SG (two copper rods, 1/2" diameter) ->
MMC (Leyden Jars, saltwater x 18, 13.6nF total)
Primary Coil (This one is two windings, 0 degree pancake coil, 8.25" inner circle, 3/8" spacing, can tap from 100uH to 390uH)

Secondary Circuit:
Secondary( 6.25" x 36" PVC, 35" winding height, 26 AWG copper magnet wire)
Top load (Toroid, 7" minor diameter, 23" major diameter, two pie pans, flexible ducting, wrapped completely in aluminum foil tape)

I have tuned this using a oscilloscope and signal generator. The secondary resonates at 130.9Khz, this is with a simulated streamer (wire). I then remove the top load and secondary coil and move the tap until the primary coil resonates at 130.9Khz.

SG goes crazy up to 3/4". I've never seen a streamer. I've tried both grounding to a ground I drove in my yard, and I've been bad in my frustration and tried grounding the secondary to my house ground as well.

The Leyden jars make a ton of noise, I started out with a sloppy build but over the past few days I've slowly improved my cap bank as I figured it was the problem. Alu tape on the outside of snapple jars. Salt water inside, topped with mineral oil. Lid has a 3" bolt through it that is secured with nuts on either side, sealed tight.

The entire thing is using #10 AWG wire for all connections.

Is my NST just not up to driving the secondary? I know I went a little crazy on the build and the toroid/secondary are monsters.

Any advice, help, suggestions, etc. Very much appreciated, I've four solid days into this build and no dice.

doctor electrons

Tue Jul 20 2010, 02:27AM

Registered Member #2390 Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381

Have you tried a breakout point? Small sharp piece of wire taped to the toroid? I am no expert but
you may have too much capacitance in your topload. This would be providing everything else is working properly.
Maybe coupling? Either way, someone here can help you get it going!!

void109

Tue Jul 20 2010, 04:36PM

Registered Member #3016 Joined: Tue Jul 20 2010, 01:55AM
Location:
Posts: 9

I did, I taped a nail to the toroid. Ultimately I even hung a bare grounded wire near the breakout point hoping to see anything - it was daylight, but I thought I saw a faint shimmering at that point between the breakout point and the grounded wire.

Herr Zapp

Tue Jul 20 2010, 08:30PM

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

void -

Your secondary and topload sizes are quite oversize for a 9/30 NST powered system. These components would be much more suitable for a higher input power level, like that provided by a 12/60 or 15/60 NST (or several paralleled 30ma NSTs).

Regardless, this coil SHOULD be capable of generating streamers IF a breakout point is used, and IF it is properly tuned.

First, a few questions:

1. Am I reading your specifications correctly, that the primary has only two turns??? ("...two windings ...")

2. How did you determine that your primary has a total inductance of 390uH? (measured or calculated?)

3. If not two turns, how many turns does it have, and what is the conductor diameter and material?

4. Are you sure that you measured the resonant frequency of your primary circuit correctly? Did you electrically short-circuit the spark gap while making the measurement? (If you truly have a 2-turn primary, your primary circuit's resonant frequency is MUCH higher than 130 KHz.)

5. What is the total length of all the wiring connecting the primary coil, the spark gap, and the capacitor bank?

6. Is the capacitance value of your salt-water capacitors measured or calculated?

7. How are you tying the outer foil of all the capacitors together?

8. For best quenching, your spark gap should be reconfigured to have at least three or four individual gaps, series connected.

9. Is your gap configured so the copper rods are parallel, or coaxial (end-to-end)?

In your response, post some photos of the primary coil, the capacitor bank, the spark gap, and a description (or sketch) of how you connected your o'scope and signal generator to the primary circuit.

Regards,
Herr Zapp

doctor electrons

Tue Jul 20 2010, 09:33PM

Registered Member #2390 Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381

Zapp will have the answers you need! Just as a note, when i was getting my drsstc going i had the same event happen
as you stated, very little breakout at the breakout point, almost just a small buzzing glow. That turned out to be a tuning
problem! As Zapp said, with the two turn primary, you may be way out of tune. He knows what he's talking about so i will
leave it to him! Out of curiosity, run your dimensions through wintesla and see what it recommends for the
toroid dimensions. Its not perfect, but it will tell you if you are in the ballpark.

void109

Wed Jul 21 2010, 12:43AM

Registered Member #3016 Joined: Tue Jul 20 2010, 01:55AM
Location:
Posts: 9

Thanks for taking a look at this Herr Zapp, to answer your questions:

1. Am I reading your specifications correctly, that the primary has only two turns??? ("...two windings ...")

No sorry, it's roughly a dozen turns, with two layers... I had put down the first 12 with copper pipe. The inductance was insufficient for reaching resonance with the equipment I had against the secondary and top load. So as an idea, I wound another layer right on top with #10 AWG copper wire, and connected in in SERIES with the first layer, so I could get that inductance plus whatever I tapped off of the first layer to reach the resonant frequency of 130.9Khz. This is where I deviated from the beaten path, and I have a deep suspicion this is the source of my troubles. Strange thing is the first layer has roughly 100uH and the second roughly 100uH but in series 390uH... This is with a BK Precision LCR meter.

2. How did you determine that your primary has a total inductance of 390uH? (measured or calculated?)

BK Precision LCR meter.

3. If not two turns, how many turns does it have, and what is the conductor diameter and material?

As above, ~12 turns, two layers, first copper 1/4" tube, second #10 AWG solid wire

4. Are you sure that you measured the resonant frequency of your primary circuit correctly? Did you electrically short-circuit the spark gap while making the measurement? (If you truly have a 2-turn primary, your primary circuit's resonant frequency is MUCH higher than 130 KHz.)

Yes I had the SG shorted, I followed the directions and schematics listed at

5. What is the total lenght of all the wiring connecting the primary coilo, the spark gap, and the capacitor bank?

I'll have to get back to you on this. But I'd guess roughly 50' in connections. The primary must have 150-200'.

6. Is the capacitance value of your salt-water capacitors measured or calculated?

Measured with the BK LCR meter

7. How are you tying the outer foil of all the capacitors together?

I initially just bundled them together. I later wrapped bare #12 solid copper wire around the foil, covered it with electrical tape, and then used grounding buses to connect the caps in parallel and the bodies in parallel.

8. For best quenching, your spark gap should be reconfigured to have at least three or four individual gaps, series connected.

I was using a 2" x 2" N42 Neo for quenching the gap. (tried both with and without). I'll try many gaps in series.

9. Is your gap configured so the copper rods are parallel, or coaxial (end-to-end)?

Coaxial (end to end).

I'll have to get back to you with certain specifics as well as photos. Everything is dismantled at this time in my garage and I'm at my office. Thanks again for helping me troubleshoot this.

Herr Zapp

Wed Jul 21 2010, 02:38AM

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

void -

OK, now we have some information to work with.

One question: Are the two layers of your primary coil wound in the same direction, or in opposite directions? (e.g. is one right-hand wound, and the other left-hand wound?)

Herr Zapp

klugesmith

Wed Jul 21 2010, 03:30AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

void109 wrote ...
No sorry, it's roughly a dozen turns, with two layers... I had put down the first 12 with copper pipe. The inductance was insufficient for reaching resonance with the equipment I had against the secondary and top load. So as an idea, I wound another layer right on top with #10 AWG copper wire, and connected in in SERIES with the first layer, so I could get that inductance plus whatever I tapped off of the first layer to reach the resonant frequency of 130.9Khz. This is where I deviated from the beaten path, and I have a deep suspicion this is the source of my troubles. Strange thing is the first layer has roughly 100uH and the second roughly 100uH but in series 390uH... This is with a BK Precision LCR meter.

Not to butt in front of Zapp, but:

The 390 uH reading is a very good sign.
When 2 coils of similar inductance are closely coupled, the inductance of both in series is close to 4x (or close to 0x, if connection polarity is reversed).

That's for the same reason that inductors wound on cores have L proportional to N squared. Consider a single coil driven with a particular di/dt, it generates a magnetic flux dB/dt which induces a voltage V = L di/dt.
Now if there 2 identical coils (or one coil with twice as many turns) in roughly the same space,
with the same di/dt, you have doubled the dB/dt. So you have doubled the induced voltage per turn,
and quadrupled the total voltage. i.e. 4x the inductance.

The right-hand / left hand question can be confusing. Say your first layer is a right-hand helix, wound from bottom to top. The current in series-connected layer 2 should circulate around the axis in the same direction. That calls for a left-hand helix, if the top of second layer is connected to top of first layer.
Your LCR meter says you got it right!

Herr Zapp

Wed Jul 21 2010, 05:40AM

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

Klugesmith -

Rather than series-connecting RH and LH wound helical coils, don't you mean Archimedean spirals?

Series connecting RH and LH wound helical coils is the Ayrton Perry winding technique, commonly used for fabricating non-inductive wire-wound resistors.

Void's primary inductance measurements would seem to indicate he has correctly connected LH and RH wound spirals, but it doesn't hurt to make sure.

Regards,
Herr Zapp

klugesmith

Wed Jul 21 2010, 07:39AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

My point holds for both helical and pancake coils: when you make the series connection
you can choose minimum or maximum inductance,
independently of whether the 2 coils have same or opposite handedness.

Consider two interleaved helixes of the same handedness, like a screw thread with two starts.
Or two interleaved flat spirals of the same handedness, like a two-start vinyl record (remember them?).
For a series connection that minimizes the inductance, the junction is a minimal U-turn connecting adjacent turns at one end of the helix or, say, the inside of the spiral. Then the external connections of the series assembly are close together at the other end / the outside edge of spiral. The net number of turns around the axis is zero. For a series connection to maximize the inductance, we'd need a jumper that skips over -all- the turns. Then external terminals would be at opposite ends of helix, or 1 inside & 1 outside connection to spiral.

Conversely, if you want -maximum- inductance with the minimal U-turn, and both external terminals brought out close together, need to overlay a RH and LH coil.

Ayrton-Perry winding uses a RH and LH helix wired in parallel.
The two branch currents advance along the axis in the same direction, while winding around it in opposite directions, to minimize the inductance.

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