The supplying transformer
In order to supply our coil, we are using a transformer built upon laboratory coils.
The first coil has 500 spires and the second 23000, which allow us to reach a tension of 10000V with a power of about 600W at the entrance.Unfortunatly, this device belongs to our former secondary school. We have to borrow it each time we want to do a demonstration.
We are using 9 or 10 capacitors (depending on the coil we used), MMC Phillips 22nF/1600V type, serially used. This kind of capacitors is quite cheap and works wonders!
After trying several types of sparkgaps that all melt, burnt or simply couldn’t be adjusted properly, we found the sparkgap we are now using, the “ladder-type”. It is perfectly adjustable, even if the circuit is live, thus avoiding us having to “blow the spark’ by compensating the formation of ozone by wider gaps. It also stands up quite well to the heat it produces during its use.
As for the maintenance, we have to rub the surface of the electrodes quite regularly because they tend to oxidize extremely quickly.
The Primary coil
Our first primary : 15 cm wide, 20 cm high. Far too small …
Our second primary coil, now quite bigger, was functional, but still a little too small, and allowed us to see wonderful primary-secondary sparks :
Our current primary coil works perfectly. Even with its 22 spires, for we only use 7 of them most of the time anyway. The supplementary spires allow us to adapt the system to our other secondary coils.
The Secondary coil
We built 3 different secondary coils :
- The first is made of around 3000 windings on a plastic tube 4cm wide with a coiling-height of 80 cm. The final electrode is made of a telescopic antenna picked up from an old radio. The base is made of a 50CD-R box weighed down with sand-filled film cans. The top is insulated by a “schtong”, a springing toy given away in Kellogg’s cereal packages. This coil’s performances are quite ridiculous. No more than 5-6 cm long sparks.
- The second secondary is the twin brother of the first one, except for two things : the final electrode is a big screw and the width of the plastic tube is now 5 cm. The performances are now far better with more than half a million volts and 15 to 20 cm long sparks. This is the coil we use for public demonstrations.
- The third one is slightly different : it has less windings and is only 60 cm high, but is now 10 cm-wide. The performances of this coil are outstanding : sparks over 30 cm-long, but in between the windings, which makes it impossible to use, even rendering it dangerous for itself.
Each coil is made with enamelled copper wire 0,2 mm wide and varnished several times with a plain wood varnish, not so as to insulate it electrically (which is completely impossible at such a voltage), but rather to keep the spires into place as well as to protect it from possible scratches or shocks.