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ExperimentsIntroductionSome interesting experiments which require high voltages are shown here. It is important that these experiments are not attempted by anyone unfamiliar with the dangers of high voltages. In many situations the combination of high voltage and current are likely to be fatal, and you don't necessarily need to be touching anything to receive a shock!
Jacob's ladder This can be set up easily and is impressive. It works well with a neon sign transformer or as here, with an ignition transformer. It is also possible to use homemade inverters which can run from low voltage supplies and with lower currents. Transformers must be of a leak-reactance type or they will overheat quickly. Two bare copper wires are connected to the secondary coil of the high voltage transformer. The wires are closer at the bottom and wider at the top, almost in a 'V'- shape. The initial spark forms at the base with the shortest gap. The air breaks down here first, but the heat generated by the arc causes the air to rise. The hot plasma arc is convected up between the wires. The plasma conducts easier than the air so it becomes longer as it rises. Eventually, the arc length becomes so long that it is easier to jump the small gap at the base again. This extinguishes the long arc at the top. The arc can have a greenish tinge because it can contain copper ions from the wires.
Ion motor The cross wires are balanced on an insulated nail. It is free to rotate and is connected to a high voltage DC supply. In this setup, the supply is negative and the tips of the cross are charged up to about 7000v. The electrons on the tips charge air molecules nearby negatively. These are then repelled by the similar charge on the wire tips. The action of the forces between the charged air molecules and the wire repelling each other causes the wire cross to rotate as shown on the video clip. Only one wire is required. The circuit will be completed via an earth path elsewhere.
X-rays X-rays can be produced by accelerating electrons from a cathode and colliding them into an anode at speed. This occurs inside valves and cathode ray tubes. However, the accelerating voltage determines the X-ray emission. The picture shows a couple of valves from early colour televisions. The triode has an X-ray warning stamped onto it. "Caution X-rays Do not operate without shielding" The video clip show the diode valve with over 20kV being applied in reverse bias and no heater current. It's not very nice to do this to valves. Don't use good ones. There is a Gieger-Muller tube beside the valve. You can hear the activity in the background increase as the voltage reaches 20kV.
Electro-magnetic Pulse A small electro-magnetic pulse (emp) can be produced with a magnetron. Running the magnetron in continuous wave mode is particularly dangerous to the eyes. In pulsed mode, little heating of tissue occurs, but large voltage gradients can be induced. The combination of voltage and energy required to pulse a magnetron is lethal. The video shows steel wool in front of the wave guide. The wool ignites when triggered by a short single microwave pulse. It then continues to burn in air.
Tesla Coil Invented by Nikola Tesla these air-core resonant transformers can produce extremely high voltages. The frequency of the output is also high. A high voltage capacitor is required in the primary circuit and these can be hard to find. This example employs a homemade dry capacitor capable of withstanding over 10kV. The coil is driven by the same transformer that is used in the 'Jacob's ladder' video. The primary coil is 12 turns of copper pipe. The secondary coil is formed by one layer of windings on the centre plastic pipe. The rod on the left is an earth return for the transformer output.
Electronic Lamp Ballast A high pressure sodium discharge lamp, pictured left, is running on an electronic ballast being supplied with 12V DC. This type of lamp requires a very high voltage to start and about 90V to run. The current must be high enough to heat the gas and evaporate the sodium amalgam. Modern electronic lamp inverters have many benefits over traditional inductive ballasts.
Lissajous figures Here is a use for all these old TV and monitor CRTs. This colour monitor CRT has it's field and line scanning coil connected up to amplifiers with variable frequency, sinusoidal inputs. The video clip shows an image obtained with the line coil frequency equal to x1, x2 and x3 the field coil frequency. |
Short Video Clips The video camera icon indicates that there is a video associated with the topic for down loading and viewing. Click on the icon to down load videos. All these experiment use very high voltages. Some have additional hazards.
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