Power Control Unit:

The most basic form of a power control unit would be an ON/OFF switch at the mains supply socket, but this would provide little protection for you and your house. A more advanced unit would provide a variable output, with voltage and current metering and numerous safety features. My controller lies somewhere between the two (see below).

[power control unit - top]

The controller has a main breaker ON/OFF switch, with a power-ON lamp, and a 10A fuse.

The output connector is activated by entering in a code number on the keypad, and the power can be shut down by pressing the emergency OFF button or by removing the tether interlock.

The output voltage is varied from 0 - 240VAC with the variac, and exits the controller through a 16A industrial connector. An indicator lamp comes on when the output is live.

An extra module was added to the controller to provide another variable output for controlling the speed of the spark gap blower motor. It is a simple solid-state dimmer circuit, fused, and routed through an IEC connector.

VariacTether interlockMain ON/OFF breakerFuseController ON indicatorOutput live indicatorPower output connectorSolid-state dimmer moduleCode entry keypadEmergency power-OFF button




Inside the controller you can see that all the space is pretty well used up. This is why I had to mount the extra dimmer circuit as an external module.
Output connectorlampBreaker, lamp and fuse holderMains filter protecting lock circuitsMain power contactorvariacMains line filterElectronic combination lock

Construction:

I was lucky enough to find a cool looking aluminium case and a scrap mainframe computer power supply unit. The chassis components from the PSU turned out to be a perfect fit for the case! So with a little bit of sawing, drilling, filing, riveting and welding, I had the makings of a portable Tesla Coil controller! The final product weighed in at 4.5 stone (30Kg)!

Safety:

In an emergency, the ability to kill the power to your coil before it can kill you is most important! My control unit uses a high current contactor (relay) to switch power to the output connector. When it is off, the output is dead. The only way to activate the contactor is to enter a combination code into the key-pad, but the contactor will only engage if the tether is set, the red EPO button is reset and the variac is at zero. Once engaged, the contactor is held on by the ouput power but it can be de-activated at any time by hitting the EPO button or pulling the tether.

Happy Home (and neighbours):

Using suitably rated fuses and/or breakers will protect your wiring from overload but one extra item is highly recommended for Tesla Coil use, a mains filter. Normally a filter is used to prevent mains-borne interferance entering a piece of equipment. As we are trying to stop interferance getting out of our TC system and into the mains, we wire the filter in backwards (swap 'line' and 'load' connections).

[mains filter]

The RF energy generated in the tank circuit can leak back through your wiring and into the house wiring. It can even spread to neighbours houses! The least that will happen is RFI (radio frequency interferance) will disrupt television receiption. The worst is that every electronic device plugged in in your house will be fried, and the neighbours will get nasty when they can't watch TV! Use a good filter!