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Small Tesla coil power supply

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Dr. ISOTOP

Sat Apr 02 2011, 06:59PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

The Class-E is definitely easier to build.
microSSTC is even easier to build.
Sadly, I never got either to work, because the cute little minibrick MOSFET I was using was broken :(

ZakWolf

Sat Apr 02 2011, 08:20PM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

I was looking at the PCB James made for the SSTC-5 mini and i was wondering what if i buy the parts and etch the board (I haven't bought any parts yet this is just an example) but the parts don't fit the holes in the PCB, i know electrolytic caps vary in size greatly and sometimes have the same ratings. How do you make sure you get the right parts for the PCB ?

Arcstarter

Sun Apr 03 2011, 02:20AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Well neither has a better output, you could make a Class E sstc with 4 times the spark length of a halfbridge coil, and vise versa.

The halfbridge is the better choice for higher power, and it does not require mosfets with 3.3 times the input voltage (mosfets see 1 times the input voltage minus ringing etc), but it requires 2 times the mosfets. Also, shoot-through is a very common problem, and it reduces efficiency and blows silicon. Also, if one mosfet dies, invariably, the other will too.

Class E is more compact and can be made as efficient as a halfbridge. But, because of the fact that the switching device will see 3.3 times the voltage input, it can be hard to get a large spark with what you have sitting around. A 600v device is required for 120vac input, and a 1200v device for 240vac input or a voltage doubler, which are hard voltages to get ahold of for mosfets, but IGBTs are a good way around the voltage problem.

Tell us what you want out of the coil, that is the only way we can help. It is impossible to tell you which would be best based on what you've told us. You say you want the best performance for the least complexity, but that is too vague. Does performance mean the length of the spark, or the power in the spark? Do you want long sparks or hot sparks?

The mini sstc nor the class E coil require scoping, but it makes it much easier to get good efficiency with a scope with both. With class E, you have to make sure the gate doesn't switch on until the zero crossing where the voltage and current are low. With a halfbridge, you have to have a good waveform out of the GDT.

ZakWolf

Sun Apr 03 2011, 03:10AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

OK, i want something that is compact that gives about 5-10 inch arcs. I was reading about Steve's tesla coils and looked at this one it looks pretty compact and James also gave me a PCB design on KICAD. Also what size secondary will i need? i have a 12in tall by 2 in wide one already wound, and i picked up a 3-1/2 inch tube (cardboard) will that work potentially?

edit: i think i will go with the half bridge, i want to make a PCB for it, whats the easiest way? photo resist or the one where you iron the circuit on then etch. Check out the SSTC 5 mini if you already haven't

ZakWolf

Tue Apr 05 2011, 07:28AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

How do you by parts for a designed PCB and make sure they fit?

James

Tue Apr 05 2011, 05:52PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

I designed the PCB around parts I already had. I provided the original files though so one could modify the layout to fit any parts. The electrolytic, film caps, and bridge rectifier are the only parts likely to vary. You can see the dimensions on the PCB and look up datasheets for parts you intend to buy and make sure they match.

ZakWolf

Tue Apr 05 2011, 07:37PM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

I canâ€™t make up my mind on what I want to build I want something simple which is the class E and a decent output which the class E can deliver. I also like to VTTC output like streamers. The circuit is smaller and requires fewer parts which arenâ€™t so costly, and would be easier to debug. Does anyone have a PCB for this on KICAD? Thanks

James

Tue Apr 05 2011, 09:26PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

Heck, build both, or all! I've got one of each design brewing, but only the VTTC has come together enough to make some sparks yet. If you wind several secondaries you can experiment. Some will work better than others, but it's hard to make one that doesn't work at all.

In a pinch you could build any one of these circuits point to point on perfboard but a PCB is less error prone. Personally I laser print on magazine paper and use a laminator to transfer the toner for etching. There's a great yahoo group forum on DIY PCB making that has been a great resource.

Dr. ISOTOP

Tue Apr 05 2011, 10:43PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

The Class E is simple enough so that you can just breadboard it.

ZakWolf

Wed Apr 06 2011, 05:39AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

I am making my parts list right now for the sstc 5 mini, I am buying from mouser there the bomb :) It would be awesome if you guys could double check it before i finish it. Also my GDT has 18 turns, how does this affect the GDT.

Sorry for the horrible quality this was taken with my camcorder camera. (the weren't meant to take pictures)

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