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Flyback based SGTC, help greatly appreciated.

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brtaman

Mon Jun 08 2009, 10:31PM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Damn plazmatron you have convinced me :D....I am going for a rotary spark gap, just got a few ideas. please post up picks of yours when you have time.

I will be updating this thread as my project continues to give updates and for trouble shooting help. Will post up pics of mine as well.

plazmatron

Wed Jun 10 2009, 12:14AM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

I have just been tidying up my flyback driven coil today, so hopefully I will photograph it tomorrow, with special attention to the tiny rotary gap for you.

Les

plazmatron

Tue Jun 16 2009, 02:12PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Sorry for the delay, I have had endless fiascos here! anyhow, here is the picture of my toy motor spark gap, so that should give you something to go on.

I have put up a short vid of the coil running at http://www.youtube.com/watch?v=lEUzLytcUgc

brtaman

Wed Jun 17 2009, 04:50PM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Hey,

Nice rotary plazmatron. Even nicer Telsa Coil. :)

Well I have finished my preliminary testing coil (also made the battery powered one for fun but blew up the CW and am now waiting for caps.)

I have to say I am quite pleased with the results especially when I look at the MMC.

It is a motley crew of caps of differing values arranged in a manner that would make you pro coilers cringe. I used what was on hand, it is only a temporary fix though, so not to worry. (also blew up a small 2kv ceramic cap).

The MMC consists of:

1x 1.6kv 10nf
1x 1.6kv 4.7nf
3x(parallel) 2kv 2.2nf (6.6nf)
and then it gets interesting:
5xparallel 2kv caps: 1nf + 0.1nf+0.33nf+0.47nf + 0.22nf (2.12nf)

Which makes the MMC: 7.2kV with 1.068 nF (Basically perfect for my coil size and flyback, based on calculations from TeslaMap)

The Secondary is:

Hight: 13.1cm
Width: 3 cm
AWG: 37-39 (hard to tell but snaps instantly, was very hard to wind)
Turns: 881-1046 turns
Frequency: 1008kHz - 849 kHz

Primary.

12 Turns of thick wire (don't know what AWG either, sorry)

The MMC consists of:

1x 1.6kv 10nf
1x 1.6kv 4.7nf
3x(parallel) 2kv 2.2nf (6.6nf)
and then it gets interesting:
5xparallel 2kv caps: 1nf + 0.1nf+0.33nf+0.47nf + 0.22nf (2.12nf)

Which makes the MMC: 7.2kV with 1.068 nF (Basically perfect for my coil size and flyback, based on calculations from TeslaMap)

Spark Gap:
Stationary spark gap. Two big lugs with ball ends. Cooled with 12v PC Fan

Power source:

Flyback driven by a 2n3055 transistor with a 250v 0.91uf cap (best performance). 5-turn Feedback 6-Turn Primary.

Draws 2.1 amps from PC **link** 24vA Puts out around 10kV@2ma(?)

It screeches like a bat out of hell so I think tuning is ballpark at the moment, on a side note I am waiting for caps so I can increase spark gap. Around 2-2.5mm at the moment.

I am quite happy with the operation of the coil for such a low input. I get 4cm arcs and around 7-9 (depends on location on torroid) cm sparks to an ungrounded but hefty screwdriver. However the coil is running a bit peculiar compared to the pictures and videos I have seen on this site and the Internets.

There is a LOT of purple (corona?) around the torroid of the coil. If I put a screwdriver within 15cm of the torroid this purple haze flows towards and sometimes even sparks. I took a very long exposure picture to show you guys what I mean. It took me a very long time to get this shot, yet the ammount of purple haze (lol) surrounding the toroid is greatly understated. The torroid is around 7cm wide the circle of haze surrounding the torroid added atleast another 7cm all around the toroid!?

Telsahaze

Is this normal behavior and I just don't see it in the videos of other coils (took a while to get this shot right as it is) Or is it due to my high frequency?

Here is an "artistic shot", long exposure with a screwdriver going around top, coil was acting up and going in and out of tune though...!?!? What was happening with the coil? I manged to somehow get rid of it but the coil would go full blast then all of a sudden quiet down for a second or two and then start blasting again then again quiet down (power drop enormous) on an irregular basis...I suspect the static spark gap?

Teslascrewdriver

I did not take and pictures of the setup as you guys would ROFL, it looks like a spaghetti diner. :) I am going to encase it in a nice box and when it is all nice and tidy I might show some shots of it in the fabrication stage. :D

Thanks
brtaman

plazmatron

Wed Jun 17 2009, 05:25PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Looking good!

The static gap, will certainly cause loss of power as it heats it, however there is the possibility that the TC output is interfering with your flyback driver too. I take it the 2n3055 is driven by a 555?

Have a look on here for Royer Circuit of Mazilli driver, to run your flyback, its a dead simple driver, that is almost indestructible and contains nothing more that a couple of mosfets, diodes, resistors, and zeners.
2n3055s waste a lot of heat switching.

The last time I saw corona like you describe was on an ignition coil driven Tesla coil. There are a number of factors that cause that. The high frequency break rate, as you already pointed out. A less than smooth toroid, will cause a lot of corona, and steal power from the system. try using a smooth metal ball as a toplad, they show up on eBay under gardening! They are used as garden ornaments.
Lack of current from the flyback may also contribute to this.

Les

brtaman

Wed Jun 17 2009, 05:32PM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Hey Plazmatron,

Thanks for the quick reply!

No unfortunately I did not have a 555 on me nor could I find an appliance to salvage it from. :P Damn programmable microchips. :) It is the stupid simple extremely inefficient 2n3005 driver with a couple resistors and a capacitor. -.- I have been looking into making the ZVS driver, I think it will greatly improve this TC, however I need to go and buy the parts, will go to the electrical store when I have time. The ZVS driver does look top notch though!

I will look around the house for a smooth toroid around my house, I remember reading that an older Christmas ornament works quite good? Will try it now.

This was just a get-it-done coil, which I will try to improve through time. First thing is my new russian army mil-spec caps (on the way) :), then a ZVS driver...then who knows? :)

Thanks
brtaman

brtaman

Thu Jun 18 2009, 11:40AM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Sorry for the double post guys.

But I think I have found a great capacitor, that could be a great 942C replacement for use European folk.

It is manufactured by WIMA, it is PP and based on what I read in the description built on practically the same principle of self healing as the 942C caps. What do you guys think, personally based on my limited TC knowledge they seem to be optimum TC caps? They are readily available, even conrad caries them. :)

Thanks
brtaman

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