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Did I waste money on these caps?

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MadMrMike

Mon Aug 02 2010, 03:23AM

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

Two more to give a better view of the wiring.

The entire set up is "rough" right now. I'm just trying to get it to work before building a nice enclosure and organizing all the wiring.

MMM

hvguy

Mon Aug 02 2010, 04:07AM

Registered Member #289 Joined: Mon Mar 06 2006, 10:45AM
Location: Conroe, TX
Posts: 154

Where's your breakout point? With a power supply that small and toroids that big you're bound to need one for tuning....

Also, those look like mylar film caps, which are notorious for poor performance in these situations. I'd still run them until they explode though

Herr Zapp

Mon Aug 02 2010, 04:27AM

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

MMM -

OK, your description seems to highlight several potential problems:

1. "Power supply: (2) 7500V 30mA NSTs 180 degrees out of phase, parallel. Output: 7500V 60mA"
To connect the HV outputs of your NSTs in parallel to double the output current, they must NOT be "180 degrees out of phase". The two out-of-phase AC waveforms would simply cancel each other, leaving a near zero output voltage. Since you say your spark gap is actively firing, it doesn't sound like you really have their outputs 180 degrees out of phase. Are your NSTs center-point grounded? If so, did you verify that each of the four secondaries in your NST bank is generating HV output (e.g. none of the secondaries is shorted)?

2. Your photos don't clearly show the interconnections between the primary coils, but once again it souinds like you have a phasing problem. If both secondaries are opposite wound, AND both primaries are opposite wound, you likely have them connected so the secondaries are in-phase, not 180 degrees out of phase.

If BOTH your secondaries were RH wound, then you would need one RH wound primary, and one LH wound primary. (Actually, you can achieve the same phasing by how you interconnect the primaries.) Look closely at the schematic for Brian Basura's Mini-Twin coil. Both his secondaries are wound in the same direction, and I believe both his primary coils are also wound in the same direction. It's in the interconnection between primaries that the "180 out-of-phase" condition is created.

Regardless which direction you have wound our primaries and secondaries, you can connect the primaries to create the out-of-phase condition for the secondaries. You can try to visualize the "right-hand rule", or simply swap the connections to one of your primary coils.

Aside from the use of DC filter caps that probably have very low pulse current ratings, your have the sides of the caps dangerously close to each other. These caps have a red stripe around the body, near one end. This indicates which lead is connected to the "outer" foil electrode. If you haven't taken the care to properly orient the caps relative to the outer foil position, you risk cap-to-cap arcing which might be very difficult to see in the inner layers of your multi-level MMC.

Unfortunately, the capacitor/transformer matching section at Deep Fried Neon recommends a capacitor value that is "resonant" with the NSTs secondary inductance. This can create a condition where the tank voltage can "ring up" to extreme values, destroying the NST and/or the capacitor. Much practical experience has shown that a "larger-than-resonant" capacitor value yields best performance while eliminating the potential for resonant voltage rise. See the section on AC resonant charging at Richie Burnett's exceptional technical-info website at:

Regards,
Herr Zapp

Dandrion

Tue Aug 03 2010, 01:57PM

Registered Member #3045 Joined: Wed Jul 28 2010, 11:02AM
Location: Manila, Philippines
Posts: 4

Hello MadMrMike,
You may wish to check this site,

While wiring my own tc, this served as my guide. Check the pri. & sec. directions. It should be both cw or both ccw, otherwise they will cancel & no sparks will come out.

Best wishes,
Dandrion

tulkas

Tue Aug 03 2010, 04:16PM

Registered Member #2865 Joined: Tue May 18 2010, 10:59AM
Location: persia
Posts: 37

hello
(sorry about saying this here but i don't want to start new topic )
does spark gap of larger capacitors , smaller than smaller capacitors ?
i mean what is effect of capacitor on current and voltage ?
i've upgraded my Cap to 38 nF but my spark gap fires on smaller distances .
and my coil works weaker . it really amazed me

william L

Wed Aug 18 2010, 02:29AM

Registered Member #3093 Joined: Mon Aug 09 2010, 11:40PM
Location:
Posts: 68

@Tulkas: Is you power supply ac, or dc? If it is ac, your capacitor is too big, so the ac voltage is both charging and discharging before it has a chance to fir, so you may only be seeing the transformers output on your spark gap.

teravolt

Wed Aug 18 2010, 04:33AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

hi MadMrMike,

1 can you draw a arc from the transformers with out the tesla
2 can you draw a arc through your spark gap if you short your primary
3 are your transformers good

MadMrMike

Thu Aug 19 2010, 04:51PM

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

1 can you draw a arc from the transformers with out the tesla
2 can you draw a arc through your spark gap if you short your primary
3 are your transformers good

Yes, yes, and yes.

To go back on what I said about the "phasing" of the NSTs, I should have said they are in phase, NOT 180 degrees out of phase. I wired them in such a way that I can draw a nice, hot arc. Sorry for the misinformation.

Further info: I removed one of the coils from the pair, securely grounded the remaining one, and tried using the setup as just a 'standard' SGTC. All I'm getting are wimpy little 1" sparks. The underlying issue doesn't seem to be one of phasing if a single coil doesn't produce an output.

I'm going to drop some money on caps I know are good, and see if that changes anything. I'm also considering scrapping the twin system and building a little magnifier instead.

MMM.

Hei

Fri Aug 20 2010, 06:34AM

Registered Member #2808 Joined: Sat Apr 17 2010, 03:25AM
Location: Hong Kong
Posts: 11

i don't think this caps are the right caps to build a TC..if look into them, they've big ESR and ESL..

MadMrMike

Fri Aug 20 2010, 01:55PM

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

i don't think this caps are the right caps to build a TC..if look into them, they've big ESR and ESL..

OK, that would make sense. Where exactly did you find that info, if I may ask?

I'm glad I didn't spend very much on them. :)

MMM

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