Tesla coil II
Wanting bigger and brighter arcs, I took a bit more time building this coil and used a better set of capacitors. These were kindly donated by Steve of http://www.scopeboy.com/tesla/ where they can be seen in a previous life with other even more impressive coils. I used the same oil ignition transformer used before for the initial HV supply. The top load capacitor below is, for the moment, part of a cafetiere.
The primary coil is made from copper brake pipe tubing. The output voltage exceeds 390kV easily but can suffer from flashovers to the primary. I suspect, as these circuits are not connected together, there is enough conductivity in the chipboard base to allow a path. The plastic collar at the base of the secondary coil is an attempt to reduce flashovers.
In the picture below, an earth return rod reduces the stress on the lower windings of the secondary coil and prevents coil flashover.
The primary circuit can be seen below. The spark gap is crudely made using three bolts. However, adjusting the hex head of the centre bolt neatly alters the spark gap size. The array of plastic film capacitors can be seen on the left. Each capacitor is 47nF 1.5kV.
My 3rd, and favourite small Tesla Coil project is this VTTC, based around an old Siemens RS1026 transmitting triode valve.
This circuit just wants to work! None of the components are critical and the bench mock-up started from first switch on.
Some long leads on the bench caused harmonics but now that it is boxed up they have gone. I have a few plans for it including
a new better tuned secondary coil.
Note: this circuit uses a full rectified MOT supplying the oscillator. The current available makes these potentially lethal. Protect against contact with any part of the circuit. The smoothing capacitors must have bleed resistors. The inline HV fuse only protects the MOT from a bridge diode short. The inductor L1 attempts to protect the diodes which are the weakest components.
Forced air cools the finned anode cap which forms a heat sink for the valve. Not sure if this is necessary but I have not reddened the anode yet. The picture shows the triode mounted horizontally. Although this was a neater fit I have since mounted it vertically to avoid possible heater/grid failure. Still needs a bit of work to improve the arc size. Perhaps a new secondary coil, as I am using an old one salvaged from an earlier TC. The circuit diagram is shown here with the RS19026 valve. The layout is shown below.
Occasionally I am involved in STEMnet activities to further science and education at schools. Using mains powered equipment for demonstrations brings many complications. As a result I prefer battery powered demonstrations. Unfortunately, I never get to demonstrate Tesla Coils or Can – crushers. While looking into running a Tesla coil from 12V via a ZVS driver I found this much neater solution at: http://skory.gylcomp.hu/tesla/mini_tesla.html . Unlike my idea, this design has no hazardous voltages other than the usual top load ones, such as slight burning sensations. Quite easy to build, small and light, yet can illuminate a 4ft fluorescent tube at a distance. Initially I kept blowing the driver FETs so often that I socket-ed them as shown below.
There is something about building Tesla Coils that creates a desire to build bigger. This coil is quite big but I still wanted it safe as possible. For this reason I have housed the primary coils internally rather than exposed on the base. It may be safer from touching but a flash over could be hidden. As it runs over a range of input voltages it can be used for various demonstrations. The left picture show a "see-through" view of the primary inside the secondary tube. circuit.