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First SSTC - need advice

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tobias

Mon Jan 04 2010, 07:32PM

Registered Member #1956 Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172

Hi all

I want to build my first Tesla Coil, and decided to go with a PLL design and fo~400 kHz. I don't want a lot of power, just a small easy to make sstc to play with pll, audio mod and so on. Only after then I will seek for power. I'm needing an advice how to setup primary and secondary, based on the caps I have.
My real problem is the capacitors. I only have these available (already bought on Farnell Brazil):

10 nF 400 V MKT (10x)
3,3 nF 250 V MKP (4x)
0,68 uF 630 V (2x)

I downloaded WinTesla and found the config above suitable to my needs.

Sec: ID 5"; H 15"; 24 AWG; 690 turns; no topload; fo=440 kHz
Pri: ID 7"; 1,5mmÂ²; 6 turns --> 0,0106 uF needed
k=0,34 (by JavaTC)

I've already built a driver board. It's a 4046 like Steve's design but using a mic4429 and a single IRF540 besides the fullbridge. Needing large heatsink on the picture.
P10000841

The 555 is an interrupter and it's disabled by the jumper.
It tracked a signal generator from 420 to 470 kHz so I guess it's working fine.

The questions that I have:
Can MKT caps do a good job since I only have them with the capacitance I need?
How much space I need to have between primary and secondary?
Is this a good design?
Any suggestions would be appreciated.

Goodchild

Mon Jan 04 2010, 09:57PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

What are the cap for? are you using them for a rail cap? if you are they need to be bigger at least 300uF or more.

For a SSTC space between the secondary and primary can be vary close depending on the power you are using. My first SSTC had a secondary diameter of 4.5" and primary diameter of 5" and I ran it up to 1200W with no flashovers.

Hope this helps

tobias

Mon Jan 04 2010, 11:59PM

Registered Member #1956 Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172

The 10 nF cap is the primary capacitor.

That helped a lot! =)

Goodchild

Tue Jan 05 2010, 12:53AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

This cap in the primary is it for DC blocking or is a resonant tank? It's probly a DC block but just checking.

If it is a DC block then I would go with something a little bit bigger I would say 1uF to 3uF at 200V once again
on my first SSTC I used a 1.3uF 300V.

tobias

Tue Jan 05 2010, 01:19PM

Registered Member #1956 Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172

The cap is for frequency match between primary and secondary. I did not though about using a DC blocking cap. Found a schematic on Richie's pages that has the two caps.

I was talking about the one between drain and source of the mosfet.

Goodchild

Tue Jan 05 2010, 04:02PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

ohh this makes a lot more sense this is a what is known as a class e SSTC. A class e coil is made to run at a Fo in the MHz zone not at ~400khz.

you can do 1 of 2 things one you could wind a smaller secondary with higher Fo at least 1MHz or you could make a different driver.

Personally I would go with the new driver because class e is a rather hard type of SSTC to start out with. One other thing that I think you would benefit from is have a self resonating driver i.e. have a feedback systems. Take a look at Steve Wards old SSTC

I could just be confused tho, is this the circuit you are using for your driver?

tobias

Tue Jan 05 2010, 04:38PM

Registered Member #1956 Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172

Yes it is a self resonant driver. The only difference is that I want to use a single mosfet.

I'm a little bit confuse now. The two softwares that I used to do the calc are WinTesla and JavaTC. Both indicates the need of a 10 nF primary cap to match the fo of pri and sec. That's just for class E? Richie describes on the theory pages that matching the primary and secondary frequencies improves the performance.

I did not wound the secondary yet =)
Did good to ask first!

Goodchild

Wed Jan 06 2010, 04:00PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

Ok these are the different kinds of tesla coil

SSTC - This is the easiest to build requires at least 2 FETs for a half bridge. SSTC doesn't need a
a tank cap it only needs a small DC block. The secondary is medium sized with a Fo between
100KHz to about 1MHz.

Class E SSTC - This is like a SSTC but has a resonate tank cap and a single switch
mode of operation. Secondary is small and Fo runs from 1Mhz to about 4MHz

DRSSTC-Best performer of the 3. Has a large resonant tank capacitor, and a Fo
between 30KHz to maybe 400KHz. Also the hardest to build.

You can't mix the components from 2 different types of tesla coil that's just asking for trouble.
What you should do is pick a design and build it to speck. You are on the right track you have the
right kind of driver the right sized secondary, you just need to build the right power stage. Also
both those programs say you need those caps is because they are made for SGTC not SSTC.

Ok now that we have that cleared (hope I'm not to confusing) for the power stage of you SSTC I recommend
you build a half bridge of MOSFETs you only need 2 MOSFETs. I know what your thinking with the single
MOSFET design that you only need 1, well in reality you will end up blowing your MOSFETs up so it's good
to have extra.

Also I may be able to help you further if you would like me to, if so can I have a link to the schematic for
the driver you are using?

tobias

Wed Jan 06 2010, 09:17PM

Registered Member #1956 Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172

Here is my schematic:

As you said, I think I ended up mixing things up. But anyway it's done now. This weekend I will give a shot to this, maybe blowing some fets.. After that I will make a suitable driver =)

Thanks for the help so far!!

Goodchild

Sat Jan 09 2010, 05:40AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

Any luck yet getting you SSTC running?

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