Instructables

Audio Modulated Solid State Tesla Coil

video Audio Modulated Solid State Tesla Coil
Here is a video of my new SSTC, this test is only at 24 volts, and its already over an inch long, hopefully, it will be much more impressive at full power.

Here is a video of the coil running in audio modulation mode at 90 volts (this was an earlier test, so the arcs became longer later on)



Finally, we have a video of the coil throwing 7" to 8" long sparks at 90 VAC input.



leviterande8 months ago
Hi, I don't understand one thing.. why does my secondary decrease to very low voltage when I set the pulse width from say 58% to 80% at the same set frequency, shouldn't I get a higher voltage???
Im making this tesla coil and i was wondering if i could run it off 240v
Xellers (author)  tesladude1232 years ago
Yes, although you won't want to use a voltage doubler, and you'll need to use higher voltage rated FETs/IGBTs. Are you going for an SSTC or a DRSSTC?
SabooZX2 years ago
Tutorial? Pwease?
i love tesla
ps what is the scematic i so want one
It's probably something similar to this: http://www.stevehv.4hv.org/SSTC5/miniSSTCfnlsch.JPG
I've built an intractable on this actually.
Plasmana3 years ago
Wow! your coil looks really good, I am at the moment building a PLL SSTC after I seem to fail at making a tesla coils work from a flyback driven by a 555 timer. All i need now is a wide diameter pipe and MOSFET's, lol

Also I am not too sure about the GDT, how many turns of wires they should be and what wire thickness too, will16swg work?
Xellers (author)  Plasmana3 years ago
Unfortunately, when I tried raising the voltage to 120VAC, all my MOSFETs started popping, I need to get some better ones.... Did you try building a coil with your ZVS driver? I've seen quite a few impressive ones on youtube.

To answer your question about the GDT, I used 16 turns of 22 AWG wire (22 or 23 SWG) on a 1.5" diameter ferrite core. The GDT is one of those components that you will need to experiment with. I do not have an oscilloscope ( D= ), so I have not tested the output waveform, I just tried it and it happened to work. If you get a nice square wave signal on the secondary side, then you are fine. Use larger components rather than smaller ones, most gate drivers can handle quite a bit of current, and it's better to have a beefier GDT than to have one that won't provide enough current to turn the MOSFETs all the way on. Good luck!

-Xellers
MOSFET's starts going off at 120VAC? That is a little bit discouraging because the schematic I got (I can't show it to you because the site I was relying on is down) requires an 240VAC input for the SSTC. I really need to get a varic...

I do happen to have a simple oscilloscope so Ill experiment with different GDT designs, thanks for your tip, it helped alot! :)

And yes, I am thinking about trying my 'failed' tesla coils with my recently built ZVS driver. I also put an 1.5nF capacitor across the HV output just for the hell of it, and damn! The sparks are absolutely ear splitting without ear protectors, this is with 36V input. I really think it should work this time.
Xellers (author)  Plasmana3 years ago
What MOSFETs are you using? My IRFP260s were good for 80VAC, but my IRFP460s (high voltage rating, lower current rating) were useless even at that voltage. All of the schematics I've seen use a variac to bring the voltage up slowly, so it's definitely worth a shot, but I'm not sure why, since the dV/dt is still the same when the device turns on and that's my guess as to what's killing it. It could also be my GDT, my signal might not be a square wave or it might not be strong enough, either one could prevent the gates from saturating properly.
Xellers (author)  Xellers3 years ago
Just out of curiosity, are you using one of the CD4046 feedback/VCO designs for your SSTC? Unfortunately, I never managed to get my PLL version working, and I'd like to see what you are able to come up with.
Because good MOSFET's are a bit expensive, I can't afford to blow them up, so im using cheap IGBT's, it is IFG4PC30F, rated at 600V and 17A. I do have a varic, however, it is rated at 1.5A which won't do me very much good, lol :(. I'll keep looking for one at car boot sales and ebay.

And yes... I am working on a CD4046 design, I found it here: http://uzzors2k.4hv.org/index.php?page=pllsstc1
That would be a bit of a gamble for me if it does not work for ya..
Xellers (author)  Plasmana3 years ago
I'm planning on buying a variac and some new MOSFETs and IGBTs for experimentation - I'll try to post something new soon. As a sidenote, if you're afraid of killing transistors but want to experiment, I'd suggest something like Steve Ward's Class E SSTC. I assembled a small, single transistor Class E in about an afternoon and it worked great (until I tried to run it in CW - hint: don't do that =P ). However, be warned that if you don't add some sort of GDT, his schematic has the tendency to kill gate drive chips...
You tried using a GDT on steve's class e? How did that work out? I have much too many UCC's that have been given an unfairly short life. :'( What core material did you use to prevent saturation at that high frequency?
Xellers (author)  spark light3 years ago
Actually, I managed to get it working pretty decently, the maximum spark length was about an inch in CW with 45V or 90V input (can't remember which it was). The original reason I switched to a GDT-based design was that my UCCs kept dying without one!
lofty4 years ago
 Nice work, my first tesla coil I made was from a cardboard tube that kitchen roll is wrapped on. I took the wire from an old motor and used some wire you use on breadboards for the primary.
For the power supply I used a flyback transformer driven by a 555 timer and had a spark gap and wine bottle capacitor.
It worked but not very impressive, only about 1~2mm discharge into the air but it could light up CRT bulbs from a few inches away.

Anyway i'm looking into solid state ones now and am planning on a proper build. Could you give me some idea of how many windings you have on each coil and what frequency you are driving the coil at and how you are driving it?

Thanks, and i'm looking forward to the next SSTC you build =)
Xellers (author)  lofty4 years ago
Thank you for your comment =] The Tesla Coil I built here closely resembles Steve Ward's Mini SSTC - I found that his feedback driven oscillator design was the simplest and (in my opinion) the most elegant way to built my first coil. In essence, a signal from an antenna is amplified by a 74HC14 inverter chip (two inverters are in series to make a buffer) and then sent through a gate drive transformer after further amplification by push-pull arrangement of two gate driver chips (one is inverting and the other isn't - I used the UCC37322 and UCC37321 because they are available as free samples from TI). The signal from the gate drive transformer then siwtches a half bridge of IRFP260 MOSFETs. Additionally, an astable 555 timer chip with variable frequency and pulse width switches the gate drive chips on and off through their enable pins. One interesting feature about this circuit is that no startup circuitry is required as the 74HC14 chip will send a short pulse to the UCC gate drivers on startup (at least that is my theory).
lofty Xellers4 years ago
I just took some pictures of my crappy coil if your interested =)

Basic setup:
555 Timer -> MOSFET Driver -> Big MOSFET -> Flyback -> Capacitor -> Spark gap -> Primary -> Secondary -> Fluorescent tube.

Light on top of coil

Light next to coil (off)

Light next to coil (on)


I'm not sure how to get it working properly though, I can only draw tiny arcs from it by holding something metal next to the breakout point.
Can you use a ZVS driver with the flybacks that have lots of plastic moulded round them ? All the circuits I have seen for them talk about winding your own primary coils and I can't do that with a moulded one. Can I?
Xellers (author)  lofty4 years ago
Yes, a ZVS driver will work well with this type of coil and can be made even with almost any modern flyback. However, before you go to more power, try tuning your secondary circuit. After I tuned by coil a bit, I managed to get 5" to 6" long sparks with a 24VDC 555 timer driver and transistor from an old TV. Also, try winding a larger coil and adding a topload, such as toroid made by wrapping AL foil around a circular fluorescent tube.
"no startup circuitry is required as the 74HC14 chip will send a short pulse to the UCC gate drivers on startup (at least that is my theory)" The reason it start up is because even with no input, the inverting driver chip is high, and the non inverting chip is low. this causes a short current to appear on the gtd, and in turn the mosfets, which sends a power pulse to the primary, then that induces a resonating voltage in the secondary, which is picked up by the antenna/74hc14, completing the circle.
Xellers (author)  spark light3 years ago
Are we talking about the same thing? I'm not talking about my SSTC, I'm talking about my LOPT-powered DC SGTC. Also, a 555 timer should still be used for starting up any SSTC because if the coil stops oscillating from feedback (which can happen when you draw a spark to a grounded probe), then the timer will compensate and the SSTC will not turn off.
I think I meant sstc. The 555 on the back of the 74hc14 isn't needed. the process stated above happens every time the driver chips are enabled. all you need is some kind of interrupter.
lofty Xellers4 years ago
Thanks for the reply.

What is the purpose of the gate drive transformer ?
I mean why can't you drive the FETs directly by the control circuit ?
Xellers (author)  lofty4 years ago
Driving the FETs directly is always a possible, however, the GDT is there to protect and isolate the logic components from the power components. Just in case of any sort of unwanted feedback or high voltage spike, the GDT keeps the driver chips (more or less) safe and keeps the logic power supply safe. It also serves to isolate transistors that may be driven by the same signal. Driving the coil without the GDT might work for a few short runs, but don't expect much before a driver chip blows. Usually, the GDT is the one thing that keeps people away from SSTCs, but it is not a difficult component to fabricate and even a sloppy-wound transformer will work (albeit not a well as one wound wound rightly with trifler wire).
spark light3 years ago
"Driving the FETs directly is always a possible, however, the GDT is there to protect and isolate the logic components from the power components. Just in case of any sort of unwanted feedback or high voltage spike, the GDT keeps the driver chips (more or less) safe and keeps the logic power supply safe. It also serves to isolate transistors that may be driven by the same signal. Driving the coil without the GDT might work for a few short runs, but don't expect much before a driver chip blows. Usually, the GDT is the one thing that keeps people away from SSTCs, but it is not a difficult component to fabricate and even a sloppy-wound transformer will work (albeit not a well as one wound wound rightly with trifler wire)." The biggest reason you CANNOT drive fets directly is because you would have to ground all the source pins, making it impossible to create a half bridge.
mihai2mn3 years ago
Is it safe to touch the sparks?Because it works on AC and shouldn't be dangerous, or i have no idea of what I'm talking about
Xellers (author)  mihai2mn3 years ago
With this particular Tesla Coil, it is safe to touch the sparks because the current is very low. However, just because it "works on AC [sic]" that doesn't mean it is safe! Try shorting out a microwave oven transformer (also "works on AC [sic]") with your body and then telling me it's safe! In fact, you probably won't be able to say much at all afterward, that is, if you survive.
johnqpublic4 years ago
Very cool!
It is a little lite on the instruction portion.
Xellers (author)  johnqpublic4 years ago
I'm just posting this as a preview to what is coming; I am building a larger PLL SSTC and will be sure to make an instructable when it is finished =]
i am looking forward to seeing that!
thanks.
Dr.Bill4 years ago
AAAHHHhhhhhhhhhhhh !!!!!!!!!!!

I Can Smell The Ozone Already !
Xellers (author)  Dr.Bill4 years ago
Actually, this coil produces surprisingly little ozone; the sparks are long, hot, and VTTC-like unlike this SGTC-type sparks that produce copious amounts of ozone.
mattccc4 years ago
sweet!!!!!!!!!!!!!!1
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