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Class E tesla coil

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ZakWolf

Tue Feb 10 2015, 03:58AM

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

Hi, Long time!

its been a long time since i have built anything and i want to start off with a class e tesla coil. I was wondering if your guys could recommend some good reading material ( i have googled class e tesla coils and haven't found much. maybe some more specific on class e amplifiers used in RF electrics that have directly influenced Class e tesla coil topology) on the subject and any schematics that are recommend for beginners. Im not looking for large sparks, this is purely to increase my knowledge and understanding of what a class e tesla is and how the work. Later on I hope to design and build me own.

Thanks eveyone

Kolas

Wed Feb 11 2015, 04:00AM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

Well I would certainly recommend Steve Ward's site. He has a very good explanation of the theory and the schematic. Terry fritz also has some good information about their operation and theory. Their sites got me going with a class E coil of my own. With some google sleuthing it shouldn't be a challenge to find either.

ZakWolf

Wed Feb 11 2015, 02:18PM

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

thanks Kolas, what is Terry Frits sight called ? I have never heard of it before.

Wolfram

Wed Feb 11 2015, 09:12PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Terry's old website is archived at

Also check out Richie Burnett's excellent site on Class-E tesla coils, and tesla coils in general.

Easily the single most comprehensive reference on the web.

Kolas

Thu Feb 12 2015, 03:20AM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

opps yeah it was Richie that had the info i intended to mention. my apologies to both for the confusion.

ZakWolf

Thu Feb 12 2015, 03:32AM

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

Wolfram wrote ...

Terry's old website is archived at

Also check out Richie Burnett's excellent site on Class-E tesla coils, and tesla coils in general.

Easily the single most comprehensive reference on the web.

Thanks :)

bob800

Thu Feb 12 2015, 11:08PM

Registered Member #18429 Joined: Sat May 18 2013, 02:05AM
Location:
Posts: 19

Also http://uzzors2k.4hv.org/index.php?page=4MHzclassE1

ZakWolf

Sat Feb 14 2015, 12:01AM

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

So I like steves coil

, especially dem sword like streamers. But I do not like how big the secondary is and that it uses an antenna to tune itself.

I must admit in the course of learning my hobbie i have greatly neglected learning what all this stuff means and does i have pretty much copied schematics :( so i really want not only to build this coil, but understand what each section is and is doing.

I am looking into getting a scope in a couple weeks because that is integral for building and seeing what the circuit is doing. For now i am just looking for information and planning.

So, from what i have read, its my understanding that class e refers to the topology used similarly to that of rf amplifiers. It utilizes zero voltage switching or close to that in order to dissipate less heat energy.

My research so far

So the low volt side consists of many transistors that "buff" and "boost" the week signal from the crystal or oscillator, unless like in steves coil where he uses a single ucc non inverting gate drive chip which i assume delivers a sufficient voltage to switch the fet?

what works better (more stable ), feed back winding or antenna for tuning?

Also what works better i have seen both, Crystal vs 555 interrupter to inject the signal.

Lastly, in uzzors coil he says "I had originally tuned everything to working order, and then foolishly decided to cut off any remaining PVC from the formers to get a more deliberate look to the project. Little did I know that the 1cm of PVC removed from the secondary and primary formers were adding vital amounts of capacitance to the setup! I was forced to make a new secondary" couldnt he have just added a top load to gain back that little bit of capacitance, like a thin metal disk or something. An why did he use two NPN transistors then that fed into an NPN and PNP pair?

So many questions, thanks everyone. I will try my best to learn this on my own so im not constantly taxing you guys for information.

Kolas

Sat Feb 14 2015, 03:05AM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

Firstly, the secondary of your own coil is really determined by the resonant frequency that you want to work with. Typically lower frequency coils are larger physically and are easier to switch. However if very fine wire is used, this can be false. Though that typically leads to much more severe problems with skin effect heating.
With respect to the closed loop versus open loop. Both work, but the closed loop has the advantage of tracking the secondary resonant frequency and keeping the switching in tune. It is also somewhat simpler in the case of the single UCC chip is the entire low side amplifier. The open loop system is one that I personally have not used, but it will for certain keep the coil oscillating near (native)resonance even when large loads and capacitive bodies come near the coil. These are both important factors to consider in the design.
It is my opinion that the feedback method is the easiest way to go. and I believe it to be stable enough.
In the case of the multiple levels of transistors and such; this is a multi stage step to amplify the signal into one powerful enough to switch the mosfet(the final stage amplifier.) In either the open or closed loop system, proper amplification is necessary. With the low logic input of the UCC gate driver chip, the whole process is in one tiny little package. So for simplicity and stability it probably cannot be beat.

The 555 has two purposes in the circuit Steve Ward uses. It firstly provides the initial start up pulse needed to cause a feedback signal, and it breaks up the continuous wave operation of the SSTC to provide interesting sound/visible/spark length effects. It also has the added benefit of lowering the power drawn from the power supply.
As far as the antenna vs feed back winding is concerned. They are both very effective. However the feedback winding will require some impedance matching to work correctly. Whereas the antenna has little tuning required (if any) There is a third option involving a current transformer as well. This method is extremely dependable and can be kept small and unnoticeable.

So if you want it to be easy, effective, and fast I'd go with redoing steve's project (like I did.) As he said, you can build it in one day, provided you already have the secondary made.
Another thing to mention is that UCC's cannot switch fast enough to drive a mosfet into the <2mhz range that I know of. So, that is possibly one reason for using a more complex system like both Richie Burnett and Uzzors2k did.
I hope that this helps clear some things up for you.

Sigurthr

Sat Feb 14 2015, 04:32AM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

Depending on what the Ciss is of your FET the UCC chips can work up to about 1MHz without a lot of complaint. They will run hot though. You can stack two UCC chips to parallel them, and I've done this for 1MHz coils where the gate/miller capacitance was uncomfortably high.

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