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Did I waste money on these caps?

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MadMrMike

Sun Aug 01 2010, 06:09PM

Registered Member #3054 Joined: Sun Aug 01 2010, 05:25PM
Location:
Posts: 13

Hi all!

I'm in the process of building a small twin coil system. At this point, everything is wired up, checked and double-checked, but I'm getting no spark. I've checked all my calculations, the tuning...everything I can think of, and still, nothing. I even tried switching from parallel to series with the primaries.

The connections are all good with short, fat wire. The spark gap is in parallel and cracks nicely when power is applied. The tank cap is in series. The power supplies are phased properly.

The only major unknown for me tho is the tank cap. It's an MMC of these:

They're wired together correctly. My capacitance meter confirms it. I emailed the company asking if perhaps these caps are polarized, and they say, "No". I'm stumped. Does anyone here have experience with these? I really hope I'm just making a silly error somewhere.

[edit] Let me know if pics would help, or if more info is needed.

Thanks!

MMM

genie109

Sun Aug 01 2010, 06:39PM

Registered Member #3019 Joined: Tue Jul 20 2010, 10:49PM
Location: In the near of Trier
Posts: 5

Hello MadMrMike

Have you a connection to the earth? Or I think the cap should bee the mistake. Or you have a spark gap in your cabling, that sparks jump over were no should bee. Pictures and some informations from the coil are good and could help to find the mistake.

Greeets genie109

PS:Sorry for my bad english but i hope i had could help you

MadMrMike

Sun Aug 01 2010, 06:57PM

Registered Member #3054 Joined: Sun Aug 01 2010, 05:25PM
Location:
Posts: 13

"Have you a connection to the earth?"

With a twin system, a ground isn't necessary. Both coils are "grounded" to each other. This brings up one point that I missed in the first post. I tried everything with only one properly grounded coil, and still got nothing, which is leading me more and more to believe that the caps are at fault.

"Or you have a spark gap in your cabling, that sparks jump over were no should bee."

I checked for that, too. I eyeballed everything in the dark, but there's no arc-over.

One (to me, far out) possibility is that the primary tuning is sooooo picky, that if I'm not right on the perfect spot, they're simply out of tune. No gray area. I doubt this tho...I've moved the tap everywhere...

Thanks for the input. I'll get some pictures taken when I get the chance.

MMM

genie109

Sun Aug 01 2010, 07:12PM

Registered Member #3019 Joined: Tue Jul 20 2010, 10:49PM
Location: In the near of Trier
Posts: 5

Are the primary holders made out of wood?

Adam Munich

Sun Aug 01 2010, 07:13PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

genie109 wrote ...

Hello MadMrMike

Have you a connection to the earth? Or I think the cap should bee the mistake. Or you have a spark gap in your cabling, that sparks jump over were no should bee. Pictures and some informations from the coil are good and could help to find the mistake.

Greeets genie109

PS:Sorry for my bad english but i hope i had could help you

I'll fix it for you because I'm bored out of my mind right now.

"Do you have a connection to the earth? There may be a mistake with the capacitor. There could be an arc in your wiring where none should be. Pictures and some information could help us find the mistake."

Also,
Bee = 20pic

Hope this helps. :)

genie109

Sun Aug 01 2010, 07:43PM

Registered Member #3019 Joined: Tue Jul 20 2010, 10:49PM
Location: In the near of Trier
Posts: 5

Hello Grenadier

Thanks that you have correct my post. But you have to remember that iÂ´m from Germany and have since 3 years English. But iÂ´m going to work on it. The school begins in 2 weeks and i had forget a lot in the holidays

.

Greets genie109

PS: Sorry for the outtake. And now back to topic!

Herr Zapp

Mon Aug 02 2010, 12:39AM

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

MMM -

If you're getting a nice, fat, bright, loud spark at your gap, then your caps are probably not the main problem, at least not yet. However, the caps you used are low-current DC filter caps, and are not at all suitable for use in a spark-gap Tesla coil primary circuit. Regardless, they may last long enough to get your coil tuned and producing some output before they fail.

To do any useful troubleshooting, we'll need ALL the vital statistics for your coil: voltage and current ratings for your HV transformer, capacitance value and configuration of your tank cap (X parallel strings of X series-connected individual caps), physical dimensions of your primary and secondary coils and their toploads, wire diameter, number of turns, and details about your spark gap. Also describe how you "phased" your HV power supplies (multiple NSTs?). And you did also connect your primary coils so your secondaries are 180 degrees out of phase, right?

If your primary/secondary phasing and interconnections are correct, I suspect that tuning is your problem. Can you post your "calculations" here that show how you determined the resonant frequency of both the primary and secondary circuits? Did you use a Tesla coil design program (JAVATC, WINTESLA, TESLACAD, etc.) to help determine all the parameters required to obtain resonance? If not, use JAVATC (

to review your design parameters, and ensure that you have enough "tuning range" in your primary coils to achieve resonance. You'll want at least two complete additional primary turns past the theoretical resonance point to allow for variables in construction, etc. Your comment that you moved the primary taps "everywhere" with no output tends to make be believe that you either have a fundamental wiring error, or that your primary and secondary circuits have such different resonant frequencies that your primary coils do not have enough adjustment range to achieve resonance with your secondary coils. Tuning will NOT be so "peaky" that you can miss the resonant tap point; the coil will generate some output anywhere +/- 1/2 a turn from the "best" tap point.

You mentioned that you tried both series and parallel primary connections. I assume that you concurrently made a large change in the tank capacitor value to maintain system resonance at the desired frequency?

You can compare your design (and verify interconnections) by examining Brian Basura's "Mini-Twin" spark gap gap coil, documented at:

Download the "Mini-Twin Whitepaper" towards the bottom of the page for all the technical details.

A series of photos of your entire setup, including all the interconnections, would be very useful.

Regards,
Herr Zapp

ScotchTapeLord

Mon Aug 02 2010, 01:35AM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635

I have tested those capacitors with my 12kV neon sign transformer, rectified, and they burnt up. They did, however, hold a charge from a flyback transformer, which I estimated to be just about as high in voltage, if not higher, than the NST. So... I don't know.

MadMrMike

Mon Aug 02 2010, 02:50AM

Registered Member #3054 Joined: Sun Aug 01 2010, 05:25PM
Location:
Posts: 13

Herr Zapp,

Here are the stats:

Power supply: (2) 7500V 30mA NSTs 180 degrees out of phase, parallel. Output: 7500V 60mA
Primaries: Flat spiral, 1/4" copper tube. 3.5" ID. 8 turns, tapped at roughly 6.5 turns. Wound in opp. directions to be 180 degrees out of phase.
Secondaries: ~1.9" x 10". ~840 turns of 30ga enameled copper. Also wound in opp. directions.
Toploads: Toroids. 12" x 2" and 8" x 2" on each coil.
Spark gap: RQ style. 6 sections of 2" x 1/2" copper pipe. ~1mm spacing. Quenched by a big muffin fan.
Tank cap: 16kV .0217uF. MMC of .003uF 4kV caps. 4 caps per string, 29 strings in parallel.

Secondary Fres, with topload: ~415 kHz
Primary Fres, with tank cap, tapped at 6.35 turns: ~415 kHz

I've built other coils in the past, and before coming here, I did as much research as I feel I possibly could. I printed and studied Brian Basura's "Mini-Twin" spark gap "Whitepapers" a few months ago in the very early stages of this project. I even went so far as to check every forum post on this website (hours and hours and hours) gleaning as much information as I could. I've learned about connecting the primaries in parallel and series; remembering the half-lamda stuff for the series connections.

Before starting this twin coil project, one of the coils was part of it's own system. I used just one of the NSTs. The MMC tank cap was rated at 12.5kV at .0106uF. It was made from cheap film caps rated at 1250V at 8200pF each. 10 in series, 13 strings in parallel. RQ spark gap. Even with a poor ground connection, it produced sparks 15" long. This is why I question my new MMC, and also why I'm here asking about it.

My calculations, I must admit, weren't done by me. I've come to find this site handy:

I'll have pictures very soon.

Thanks for your help.

MMM

MadMrMike

Mon Aug 02 2010, 03:15AM

Registered Member #3054 Joined: Sun Aug 01 2010, 05:25PM
Location:
Posts: 13

Pictures! Hopefully these'll show enough detail.

The overall setup showing only one of the coils.

Please let me know if these provide enough detail.

MMM.

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