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Help me make a better SGTC.

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LAN_403

Platinum

Sun Dec 25 2011, 08:46PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

I want to make a better SGTC, I've made one with a 20W flyback driver, and some homemade bottle capacitors. Can you tell me what I need to get better sparks?

The driver obviously needs upgrading, so I'm getting a ZVS from Tom Williamson.

The Lightning Stalker

Sun Dec 25 2011, 09:43PM

Registered Member #4230 Joined: Sat Nov 26 2011, 05:50AM
Location: Socketville
Posts: 53

You might want to abandon the flyback entirely and go with an ignition coil(s), or better yet, a NST, OBIT, or some MOT arrangement. You could also try winding your own lower voltage, higher current flyback transformer on a large ferrite core. You'd still need high voltage fast diodes and good filter chokes or they'll fail from the back EMF.

You'll also probably want to switch to an MMC or homemade polyethylene for your caps.

Platinum

Sun Dec 25 2011, 10:06PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

I have looked for NST's and even for a 5KV 25ma is Â£40, and the rest are absurd prices, so I can't get an NST.

I don't even have the tool to make a homemade rolled cap, only soda bottle caps. How many bottle caps will I need for a useful SGTC? Atm I have 2x 2l bottle caps.

Thanks!

Sulaiman

Mon Dec 26 2011, 10:09AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Unfortunately the supply to the primary is always a problem
an NST is ideal, but not cheap and not difficult to kill
- tv/monitor flybacks are low power but easily available
- ignition coils are commonly audible and not particularly cheap/available in good condition and not high power anyway
- large eht transformers are for the experienced/committed
- solid state/transistor direct drive is the 'in' thing
=========================================
I think that a 20 W flyback supply is quite a good start,
(fairly 'safe' and 'scope-able)
each component of an sgtc is important and
building and modifying and tuning of each component is educational and
gives a better idea of how to spend your cash for the next version.
Once you have a working sgtc it's interesting to see how far you can improve it.

For an impressive TC think Â£100's

Fisherdog3

Mon Dec 26 2011, 06:55PM

Registered Member #4290 Joined: Sat Dec 24 2011, 06:08PM
Location:
Posts: 5

I've found that antique shops selling old neon signs often have a few extra nst's lying around. I got a 12kv 30ma for 20 USD.

Platinum

Mon Dec 26 2011, 07:48PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

My town isn't very good for, well anything, not many shops here. Stuff like tesco's and that's it lol.

I think the main hindrance in the SGTC I made is the capacitor, the spark gap tunes when the gap is 2mm apart, so I think there is not enough voltage in the capacitor.

The 20W flyback driver I have is from a CFL ballast, it is very low power, but I'm getting a ZVS, so I will use that at about 100W.

Tetris

Mon Dec 26 2011, 08:46PM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

I have a horrible SGTC too. My NST has too "low" a voltage for the size of coil I built, but it is too late to change it. I had a 7500V, 30mA NST, but that is the bare minimum voltage. Also... homemade leyden jar caps are crappy. I had four leyden jars, but the capacitance of them was way too low. Use JavaTC to plug in the values of your coil, and find the capacitance needed. Make sure you also have the right number of turns on your secondary. For larger coils and not the desktop models (which if you want, use a SSTC, SGTCs are harder to make mini), you need approximately 1200 turns. Too little and there won't be as much voltage in the secondary. Too much and there will be too much resistance. I made a mistake and did 1500 turns. It's too late to change that now for me though. As for capacitors, go with an MMC. You can find them online and depending on your coil's demands, it can be 20-60 bucks. My coil needs MMCs, and I await some from Kizmo. One thing to remember. Make sure the capacitance is not near the resonance of the NST or MOT or whatever transformer you choose. Just like how singing at the resonant pitch of a wine glass shatters it, the transformer can die. That aside, if you can hear yourself talk over your spark gap, it's not built right. Also do you have a safety spark gap? It's put in parallel to the caps and adjusted to a distance just at the right place where it won't arc over normally. There is a middle pin that goes right in the middle of the two ones, and at that distance where it won't arc from either side. This middle pin is grounded. Use that to prevent your NST from dying if you use an NST. Though they can be shorted forever, they are voltage sensitive. Give details of your coil size and stuff, and your intended spark length. Then we can help you more.

Platinum

Mon Dec 26 2011, 08:49PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

Thanks for your post, I think now I'm going to completely rebuild a new SGTC.

thearisen

Sun Jan 15 2012, 10:10PM

Registered Member #4341 Joined: Sun Jan 15 2012, 07:09PM
Location: UK
Posts: 3

Highvoltagechick has pretty much the right idea here, best bet is to model your system in scantesla/javatc and go from there. You'll want more input power and a better quality more appropriately sized cap (make a small MMC) - also more topload to go with it I'm guessing.

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