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Poor SGTC results Problem

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EDY19

Fri Jun 23 2006, 03:01AM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

Ahh, 4 bottles are not quite enough. I tried it on wintesla, and for 4000VAC (two MOTs in series) and .5A (~2kW, quite large) the suggested capacitance is .33uf. Also, if you want to use those two transformers, you WILL need a bigger secondary. Even rating the transformers for .25A gives a capacitance value of .165uf, and when each bottle is about 800pf, your total is only .0032uf. So either make a LOT of bottles (412.5

) or make an MMC

Michael W.

Fri Jun 23 2006, 03:11AM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

I've also used a level shifter on the MOT's (to produce about 8KV?) with an MOT to ballast the lot...Mabye I need an MMC but that doesn't solve the resonance problem. If the coils out of sync it could blow the MMC, could it not?

Coronafix

Fri Jun 23 2006, 03:45AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

I'd suggest making a poly rolled cap, or stacking foil and poly vertically and immersing in mineral oil.
I made a salt water cap and it measures at 600pF, that means for my static gap 15kv60ma NST, I need 30 bottles!
I don't think your 6 will be anywhere near enough when you're using a dual MOT.

Michael W.

Fri Jun 23 2006, 04:15AM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

Well I'm sure as not ready to take on the daunting task of making 30 to 412 bottle Caps. I'm thinking more of a stacked cap...how about plastic plates and foil somthing along the line of this....How many plates do you think I'd need? (that is, if it works..

)

Desmogod

Fri Jun 23 2006, 04:37AM

Registered Member #139 Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358

Coronafix

Fri Jun 23 2006, 07:00AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

Here is another good one.

EDY19

Fri Jun 23 2006, 01:03PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

"I need an MMC but that doesn't solve the resonance problem. If the coils out of sync it could blow the MMC, could it not?"

A MMC would solve the resonance problem. I'm guessing you have come nowhere near the correct tuning for this coil. Since MOTs have a High current, to get even close to 1kW from the coil, you will need bigger capacitors, and the easiest and most efficient way is with a MMC. Just think about it- if the capacitors are two small, and the the MOT can supply a high current, the capacitors are holding nowhere near the charge that the MOT could supply. And, it wouldn't set you back too far price wise. They make .15uf 2kV capacitors that would be about perfect, and you could definatly make longer sparks! I would suggest putting 4 caps in series, and then 4 of these in parallel to get ~.33uf at about 8kV. This would do a lot of good, and if you only wanted one MOT (still large enough for BIG sparks) you couls just use 2 parallel strings, and your output would be greatly increased!

Michael W.

Fri Jun 23 2006, 04:34PM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

42L's .15uf 2KV, 4 Bucks a pop, thats 4 strings of 4, 16, is $64 plus shipping, and I'm canadian...

Anywhere cheaper or anyone have any they want to sell off?

Marko

Fri Jun 23 2006, 06:02PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I think you need to improve much more things over there before making monster 150nF 8kV capacitor for such small coil.

Even TDU's 18 inch coil uses 'just' 90nF at about same voltage.

Powering it with two MOT's is just silly for 5cm wide secondary.
You'l be just about enough with small 100W mazzili driver (by freau's formula this would be a 17 inch spark, I guess half of it would be pretty good for this coil).

Bottle caps are fine, especially because they allow you high-ish charging voltage without blowing up (enough bang energy with small capacitance).

Current 4-5nF is absolutely fine, if you really feel like such you can add some more bottles there.

Some more apsolutely necessary things are simple multi-static gap, for this power level few closely-placed metal nuts can be a good example, then a good ground (mains ground or water pipe), and invetable, topload.
Topload can be a foil covered sphere or toroid, two welded round bowls, or anything without sharp edges you can find.

This is especially important for such a small coil with hign no-topload resonant frequency.

Use a fuse clip to tune the coil.

All aproximate calculations you can do using wintesla, TCCAD, or any program you like. You have entire primary to tap.

Good luck, and don't get dissapointed or nervous just at the beggining.

Michael W.

Fri Jun 23 2006, 06:08PM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

I'll use my flyback driver (produces up to 3 inch arcs) to power my coil, I'll make a new spark gap, and I'm going to try and tune the LC Circuit with an O-scope/Sig. Gen. this weekend...I have a top load suitable but I thought since with out a topload the max arc was about an inch, what would a larger topload do...I'll try it

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