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Flyback Powered Tesla Coil

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LAN_403

fatboyslim

Tue Jul 14 2009, 07:28AM

Registered Member #1779 Joined: Sat Oct 25 2008, 11:05AM
Location:
Posts: 32

Hi, I had started work on a table top flyback tesla coil, but after completing its build and running it, its performance was very low, sparks mabey only 0.5-1 inch to a flurotube.

SPECIFICATIONS
555 Flyback Driver running on 16v at 5.00 amps
Primary AWG 12 Flat Spiral
Capacitor: 20kv 8nF MMC
Secondary: 1 inch Diameter, 20cm Secondary. Estimated about 700-1000 turns
Static Spark Gap

The problem which i see is that the spark gap fires quite slowly compared to my full size tesla coil. You can hear the individual cracks of the spark gap. What i was wondering about is what i can do to this set up to improve the sparks coming off it. Is my flyback regulating too little current to charge the capacitors. I am trying to achieve visible streamers.

Please Help

Thanks

Fatboyslim

brtaman

Tue Jul 14 2009, 09:42AM

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

Hey, I have limited experience in the HV field but I have gained quite some insight with flyback powered SGTC's. Let me see, if I can assist you.

First, have you tried adjusting the spark gap to a shorter distance (sorry have to ask :)).

Second, I believe your MMC to be way over spec in terms of capacitance(IMO which doesn't mean a whole lot). My Flyback SGTC, which seems to be performing quite nice

, hit its sweet spot at 3.3nf and this is with 120W input. I think the simple fact is that your flyback just isn't outputting enough to fill the tank cap at a reasonable rate. I would suggest adjusting the MMC to around 5nf to see if there is any improvement.

Hope I was of some assistance.

Thanks
brtaman

fatboyslim

Tue Jul 14 2009, 10:40AM

Registered Member #1779 Joined: Sat Oct 25 2008, 11:05AM
Location:
Posts: 32

WOW your TC amazing. When i built my larger one i used 8nf as my capacitor bank and achieved good 12-15 inch streamers. So thank you. I will definitely change the capacitance to 5nF. Will lowering the capacitance make the spark gap trigger faster?

Oh and yes i did try making my SG smaller. its roughly about 5-7mm. If it helps ill reduce it.

Should i increase the AWG of my primary coil

Thanks

brtaman

Tue Jul 14 2009, 11:08AM

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

Hey,

Yeah a smaller MMC capacitance will definitely make the spark gap trigger faster. I think a sub 5nF value will be ideal for your coil based on input. Just remember to retune the primary for the new capacitance.

I think your main problem ATM is the size of your spark gap! 5-7mm is much too much for the flyback, this is the main culprit behind the slow fire rate. The thing with these coils is that the higher the breakrate the longer the sparks and streamers, mine functions best with around 1-3mm spark gap spacing. Before you do anything to your coil decrease the spark gap to around 1-2mm and move out from there, should give you much better performance.

What AWG do you have on your primary? An increase will help, but it doesn't do wonders at our relatively low power levels.

Thanks
brtaman

fatboyslim

Tue Jul 14 2009, 12:18PM

Registered Member #1779 Joined: Sat Oct 25 2008, 11:05AM
Location:
Posts: 32

I use 12AWG wire for my primary. Oh and BTW the flyback driver i am using is not a ZVS it is a basic flyback driver from this website :

Does this require any changes due to this fact.

Thank you so much for all the advice

brtaman

Tue Jul 14 2009, 12:28PM

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

Hey,

Sorry didn't notice that you already posted your Primary specs.

No besides the fact that the output of the flyback will be lower than with a ZVS there really isn't much different. Do you have any videos of the arcs that your flyback was making before you installed it into the TC circuit?

First just adjust your spark gap electrodes much closer, then start playing around with the tank cap size. I think you will notice quite a large performance increase just from this.

NP about the advice, glad to help.

Thanks
brtaman

fatboyslim

Tue Jul 14 2009, 12:31PM

Registered Member #1779 Joined: Sat Oct 25 2008, 11:05AM
Location:
Posts: 32

Thanks, i will do so tomorrow. Right now it is 12:30 am in the morning so i will get a vid up later on today, not right now because it would wake everyone up. Ha Ha.

Thanks

Sulaiman

Tue Jul 14 2009, 06:41PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

I have a few ideas;

1) Check the flyback output and primary circuit.
- connect the flyback output across your spark gap
- connect the primary coil and capacitor (mmc) across the spark gap
(This is the 'standard'/best configuration)
- Increase the gap until it fires erratically, then set the gap about 10% shorter.
The sound from the spark gap should be continuous, loud and 'sharp'
with a whitish-blue colour.
If the arc in the spark gap is any other colour then you need to blow air across the gap
(try a vacuum cleaner on 'blow') or worst-case redesign the gap.
The parts of the spark gap where the arc forms must be smooth and round, NOT 'pointy'

2) Match the primary and secondary resonant frequencies;
You can vary
- primary capacitance (by using more or less capacitors - don't over-volt the caps!)
- primary inductance (by 'tapping' the coil at different points)(the 'standard' method)
- secondary capacitance (by adding or subtracting topload capacitance, larger or smaller or multiple conducting objects such as tin cans, cooking pots/bowls etc.)
YOU WILL KNOW WHEN THE PRI & SEC FREQUENCIES ARE MATCHED

You could get a bit more technical by using an online TC calculator
or calculateby hand using Wheeler and Medhurst formulas.
If you have a 'scope and sig-gen then you can measure the pri & sec resonant frequencies.

Just keep at it, you'll find the 'sweet-spot' eventually.

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