A little help with first Tesla Coil

[Det_pleasant]

Hey
I'm new to this forum and just wanted a little help with my first Tesla Coil.
I have tried to employ Steve Ward's SSTC 2 half bridge Circuit
I have a primary with 7 turns of 1.6 mm enameled copper wire
And a secondary with approx 1500 turns of 0.2 mm enameled copper wire
the length of the coil is 39 cm
the topload is just some PVC pipes in a toroid like shape wrapped in a few layers of Aluminum foil
(couldn't find a proper toroid)
The driver circuitry follows Steve Wards SSTC 2 build on bread and perf board

When I powered it on for the first time it managed to power a CFL very weakly
I had assumed that a decent sized coil like this would be able to generate arcs of small if not decent length, let alone power a CFL
I noticed a few things on the times we powered it up
There was a small crackling noise from the free end of the Secondary and some coming from the 20 A 600V diode
There was also no change in performance Between when the feedback antenna was connected and not connected
This lead me to believe that there was some problem with the feedback mechanism
If anyone has any suggestions or needs more info
I would be grateful to hear them or supply said info
Thank you 

[Laci]

Hello and welcome to the HVF!
You might have problems with your feedback system,but without some more informations I'm really not sure,however I experienced the same problems in the past.Making the driver on a breadboard can cause problems because it picks up many noise from your coil.
Can you upload please some pictures about your design?

Also Steve Ward's SSTC 2 uses the TL494 PWM IC,which generates a fixed frequency.If the antenna feedback signal is not strong enough,your coil will run on the set frequency,most likely out of tune,which causes poor output and at too high frequencies more spikes at the transistors,so the diodes have hard job!

To minimize the parts list and modernize the design,I recommend you to take a look at Steve's SSTC 5 or any of the Kaizer SSTC drivers,which worked flawlessly for me.

http://kaizerpowerelectronics.dk/tesla-coils/kaizer-sstc-i/

http://kaizerpowerelectronics.dk/tesla-coils/kaizer-sstc-ii/

http://kaizerpowerelectronics.dk/tesla-coils/kaizer-sstc-iii/

[Det_pleasant]

Sorry for the double post
These are the pictures
Sorry for the messy circuitry
I'm kinda new to all this
Thank you
I will check out those links

[Laci]

You can always modify your previous post,just like I did a couple of times in a minute ago.

The secondary looks nice,maybe cut the uncovered top of it if it's possible.The topload looks good,but the primary turns seems too thin for me,which have high impedance at high frequencies,so you can push less amount of current  through them and also low primary to secondary magnetic field coupling that makes the energy transfer hard.

What about the gate drive waveform?Have you got an oscilloscope?What is the resonant frequency of your secondary coil?What is your input voltage?

By the way thanks for the pictures!

[Det_pleasant]

That's is one of the problems I face
I do not have an Oscilloscope or an LCR meter to check wave forms and inductance
Which is one of the reasons why i choose the SSTC 2 as the feed back mechanism would ensure the correct frequency was generated
Input Voltage is 220 Volts AC which is stepped down and rectified as needed
So 12-13 volts DC into the gate driver and 5 volts into the oscillator
 

Thank you for the advice on the posting system, I'll be sure to follow it from next time

[Laci]

Finding the resonant frequency of your secondary is not really hard,the JavaTC calculator usually calculates it pretty accurate.
http://www.classictesla.com/java/javatc/javatc.html

The problem is the transistors gate drive waveform.Using a inappropriate core for the gate drive transformer makes the transistors switch badly,even if it looks nice.You can buy cores designed for this puprose,but making a good GDT without an oscilloscope is not easy.

What type of transistors are you using?For MOSFETs the 12V driving should be enough,but the 5V going into the bridge(is this actually what you called "oscillator"?)is a bit too weak.You can try a bit higher voltages safely up to like 30V,no more yet.

Here is the evolution of my SSTC,I described many problems like you.Eventually the results were amazing for me,almost 50cm sparks.I wish you the same and more,and a great time while working with your project!
https://highvoltageforum.net/index.php?topic=122.0

[Mads Barnkob]

Welcome to HVF

As you can dimly light up a CFL tube, you got some HF field present, that is a good sign that something is working.

First, have you tried to change the phasing of your primary coil? If you want to know why this matters in a SSTC, read more here: https://highvoltageforum.net/index.php?topic=431.0

Second, if it was just the driver low voltage section that was powered, this would still be enough to leak energy through the GDT to show that behaviour. So you could have a defective bridge.

[Downunder35m]

You are dealing with a lot of power and high frequencies.
The connections on the pref board and so on cause a lot of interference, either themself or by picking it up.
You should simplyfy the thing and make a small circuit board or at least keep everything as close and short as possible.
The primary needs much thicker wire.
Even at just 150W it would have far too much losses due to the resistance.
HF causes the skin effect, so all the power travels on the outer "skin" of your wire.
Try 4mm wire as used in cars or speaker wire of similar thickness.
The spacing between the turns should be considered for proximity effects too, you don't want them too close....

[Teravolt]

hi Det_pleasant if you don't mind me asking what country are you in and can you get a surplus o-scope? even a 20MHz would help. this may be necessary for you to proceed.  everything in your circuit is placed in a mish mosh way on your protoboard and this makes it hard to troubleshoot. If it were me I would find my schematic and line all the devices in a row down one board and build your regulator board on a point to point solder board. what I did is build my power supply next to the protoboards like +5, -5, 15, -15, 24. build each peace and test it and then hook up the blocks. eventually you will find your own style of assembly. Hear is my photos in stages of my current project

[Det_pleasant]

Hey
Thanks for all the advice
I managed to get my hands on a cathode ray tube 10MHz oscilloscope and an LCR meter.
After probing the GDT, I managed to see that there was large signal distortion and I rewound the transformer.
I have a 240 V city line

After seeing how the circuit I had fail in multiple places, I decided to try the SSTC 5 by steve ward.
It is a simpler circuit. the only problem is that I can't seem to find UCC chips in my city
Will the MIC 4420 and the TC 429 be suitable replacements ?

[Laci]

The MIC4420 and the TC4429 do not have enable pins,which means that you have to add some extra components to the circuit to make the arcs interrupted,for example and AND gate between the feedback from the 74HC14 and the interrupter.However you can use them in CW(constant wave)mode like that,but only at lower voltages,definitely not at 240V city line while testing.
The 555 timer to start the oscillation is not necessary with a good antenna.See this schematic:
http://kaizerpowerelectronics.dk/wp-content/gallery/2009_01_22_-_kaizer_SSTC_I/KaizerSSTCIdriverschematic.gif

Congratulations for the new equipments,looking forward to see the updates!

[Det_pleasant]

What else could be a good replacement for the UCC chips
Preferably in TC or MIC as those are available near me

[Laci]

Google your available parts and the datasheet will say if they have enable pin.I was also looking for those kind of chips,but ended up buying the UCCs from another country.Maybe someone else can mention a good driver from those...