Amplitude Modulated Tesla Coil: First the power, Now the control!

last updated:03 Dec 2003

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High Power AM Tesla Coil

This set of experiments demonstrates that not only do I have the power, But I can have absolute control over it. I am using my new tesla coil wound on a cardboard form for concrete posts, 8" in diameter 2' tall. I used 28 gauge wire to wind this one. It seems to work pretty well. Above left, is a pic of a tesla coil being AM or pulse modulated at about 10 Hz. The sparks look somewhat normal, accompanied by the usual raaat-tat-tat-tat type sound. I do have the power turned down a little, because when I use higher frequency modulation rates, it is very easy to blow out FETs. I believe it is because of the back ringing of the coil across fets when in the off state, causes the disasters out come. A little trick I learned to get longer sparks with a solid state tesla coils, it to detune the drive frequency, a little lower than the actual resonance. The higher the power you run at, the more you should detune. This is probably because the plasma streamer will detune the coils resonance, and you want maximum power out put, while the streamer is being formed.

Above, To the right, is a streamer produced by a tesla coil being modulated at over 1 kHz. Notice that the streamer becoms noticably shorter and brush like. It also splits in to a 'V' type formation for some unknown reason. Like to see kHz modulation done with a normal spark gap variety tesla coil. It is very also unusual, because the streamer makes a sound at the modulation frequency. As you tune the frequency, the pitch goes up and down, almost like a plasma speaker or spark-audio transducer. I have included a video below, that demonstrated the AM tesla coil in action.

Download Video of AM Tesla Coil (2.5MB)

OK, here is my new version 4.2 Power driver circuit, able to put out Kilowatt power levels D.C. to MHz. It is also super broad band, not being limited by isolation transformers. More than half of the components are surface mounts, making the devie very compact, and It has BNC connectors, so it is convient to hook up to RG-58 coax cable, and pump the power anywhere you need to. I am currently testing the next version and will soon be able to make available as a kit, shematic, etched PC board, or parts, if there is enough interest. I figure I will be able to make the kits available for around $250. Presently I am working on a few minor detail to push the frequency responce up past the MHz range, but this present model is more than adequate for for nicely driving your favorite tesla coil.

Here is a nifty little gem that makes high power operation of a solid state tesla coil, safe for the fets. I have a second primary type coil in parallel with the driver coil. This second primary has a very short spark gap, which shorts out the coil when the ringing becomes excessive, and disipates the excess energy, before it can ring back through the primary and kill any fets. To the left is a close up of the little spark gap, and to the right is the same gap fireing. The flash if very bright, momentarily blinding the video camera. This gap has enable me to run the coil at much higher power, without blowing out my high power RF AMP (Power Driver Circuit).

Ok, In the picture above, is a beautiful demonstration of Tesla dream, the wireless transmission of electrical energy. I have two tesla coils, which have a common resonance around 110kHz. There is a little neon bulb on the large tranmitting coil, which flashes as the coil is pulse modulated, and there is a neon bulb in the ground path of the smaller, passive coil. When the large coil is pulsed, the smaller coil receives some of the energy, and its neon bulb also lights, even though there is no physical electrical connection. Of course this is the principal that radios, cell phone, TV's,wireless eather net, etc. work on. Of course, we all know that Tesla was the true inventer of Radio, and not that other guy who's name starts with 'M'.

An interesting thing happend the other day in the lab. And those of you who are experimentalists, will immedialty know that 'interesting' translates to equal something BAD. Yes, I turned on my little Tesla coil, and there were no spark comming out. This usually means that I had blown a couple of fets, but the Bird power meter is telling me I am putting out a good amount of RF power. So, What would any one in my position do, given the circumstances? Crank up the power, right? The coil started smoking, and stinking, like you can't believe. The smoke was rolling out the base of the coil. My first reaction was, this can't be good. But what the heck is going on here? I took the coil out of the system, and examined it more closely. Some of the winding were a little darkened, and the insolation was melted off them, in a complete ring around the coil. I had to unwind about an inch of the coil to see what was going on underneath. It appears that a burnt carbon ring formed around the base of the coil. It formed a complete ring. I imagine that it formed slowly, but once the carbon ring made it all the way around the PVC pipe, it completely shorted out the coils. By putting more power in to the coil, I was only heating up the carbon start starting the PVC a smoking. I doubt you will ever see anything like this in the spark gap type coils. (the coil was being run in C.W. mode at the time of destruction.) The RF levels to do this type of dammage are much too high.

And now for the word of the day. NAFTA, Just say NO. It seems apparent that polititions of this great nation have no reguard for the working majority of the people that live here. These NEW Labor Laws must be changed back, otherwise all of the wealth that you, your parants, and your grand parents have work so hard for, for the past 250 years, in persuing the Great American Dream, will soon lost, in to the pockets of a few special interest groups.

This will inevitably leave America to become nothing more than a third world nation. Look around, it is already happening, Just as Ross Perot said it would. Yes, I have heard those say that bad times will pass, and they use the example of bad times in the recent past to show that things will eventually get better some how (but they never say how or when).

The truth is, that they did not go back far enough back in to history. Compare apples to apples why don't we???. Try looking back in history to a time before these laws were in place to protect the American people, The era of Robber Barrons and Sweat Shops, right here in the US. Without these laws, there is no mechaism for recovery. (period) Is it really resonable to assume things will ever get better, when we are still heading in the absolutly wrong direction???

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