[shortlink url=”http://tinyurl.com/msd4o8v” title=”Continued From V8 Tesla Engine”]

After playing with the V8 Tesla engine I realised that I could build a stand on tesla coil. The lack of mains power could make this “fairly” safe.

So I started with a topload that was big enough and strong enough to stand on. I started with a pair of 110mm PVC tubes and joined them together. The thought was to make an oval tesla coil (big mistake).

After winding the secondary, by hand (1000T of 0.33mm wire ) on to the former I started to realise that there was a problem, the wire stretched slightly and started to sag between the two tubes. To give the wire some support I wound PVC tape around the coils as I completed them. This was partially successful, but as I had nothing to loose so I continued.

The Topload needed to be strong enough to

stand on too and smooth and an oval.

So I started with an MDF former of 3 oval sheets spaced to a total height of 2.5″, and an external wrap of pipe lagging to give the external shape.

Over this I added paper mache and then a covering of plaster and PVA glue to give it strength. This last layer could be sanded to smooth out the edges.

The Primary, I quickly roughed out from 50′ of 5mm break pipe held in an oval spiral with cable ties and adhesive.

The output from the V8 tesla engine is fed into a primary cap and an crude sparkgap.

Here is the coil working at the Nottingham Gaussfest.

Note that the problems with the secondary coil are starting to show with a breakout at the bottom.

But it was worth having a go at standing out the coil. After a while I found that the tuning point changed only a single turn when I was standing on the coil.

Below is a video of the first run with me on top.

So I realised that the secondary needed to be re-built The pictures below show the damage.

So the rebuild begins

This time I’ve packed out the space with some cardboard in the void between the PVC pipes and sheets under the coil bridging the two pipes. The cardboard is held in place with many layers of adhesive craft paper that was varnished before the wire was wound on.

The finished article looks a load better then the old one, but there is still some minor ‘droopage’ between turns. So the coil was heavily varnished after winding.

Hopefully it will not suffer the same breakouts as the old.

Also I decided to clean and re-mount the sparkgap the old copper pipe gaps were a little? corroded.

The Sparkgap is mounted on to a channelled acrlyic chamber that allows a high volume fan to blow air over the gaps for cooling and more importantly spark quenching.

Better results from the new coil

I have been asked this question so many time I thought I aught to write down the answer.

Musical tesla coils are fairly common now and there are many videos of them working, but what causes the noise.

So lets start with the basics. Most electronic tesla coils don’t run continuously (Ill come back to CW coils later). To maintain a large spark output current in the primary circuit is key, to get the best out of the components the coils are driven for short periods of time, at high currents, quite often exceeding the continuous rating of the drivers.  During this short ‘on’ period, power is stored as in the primary and secondary coil. As soon as the power is turned off the stored energy is transformed into a high voltage high frequency pulse. It is this pulse that you see as the discharge from the top of the coil.

Creating hot plasma in the atmosphere has an effect, the air heats up to thousands of degrees C in a microsecond or so. This expanding air causes a sound wave that you hear as a click. (or a bang with real lightning, its just a matter of scale.)

So, if you repeat this process at say 263 times a second, you will hear an audio tone at middle C

Music can be played by controlling the length and frequency of the pulses you send to the coil. With these coils getting the frequency and length information is relatively simple from a MIDI audio source via a suitably programmed microprocessor.

Due to the pulsed nature of the coil real audio (e.g speech,singing etc) cannot be rendered.

OK, I mentioned CW (Constant or Carrier wave) Tesla coils
With CW coils the power isn’t interrupted they are driven constantly. Their output is essentially silent (You do get a hiss at lower frequencies due to variations in the spark output). To get music from these coils you vary the power going in to them in a very similar way to an AM radio transmitter. There is two ways of achieving this.
1) You control the voltage to the driver therefor controlling the power
2) You vary the frequency of the drive (FM modulation), The tuned circuit formed by the secondary gives maximum output only at the central frequency, so the effective output power is varied as the frequency is varied.

As the power is continuous, you can’t gain any power advantage by short pulses and neither do you get the voltage gain by the release of the stored power in the secondary so the sparks are smaller than a pulsed coil.

But, you can render speech, singing and any instrument can be played due to the almost radio style modulation. Plasma speakers are made using this technique.