Sir Pedro HV Generator

Free Web Hosting Provider - Web Hosting - E-commerce - High Speed Internet - Free Web Page

WARNING: This project is only for adults with a sound knowledge of electricity and electronics. Working with high voltages and currents carelessly can cause personal injury and damage to property. If you build this project it is at your own risk and responsibility ! ! !

With occasion of building an electrostatic motor I feel the need of a high voltage generator to drive this motor. Among the various methods of getting high voltage, one of the simplest is using an ignition car coil. The only problem is that car coils have to be driven with a series of electric pulses of a specific frequency, or at least among a certain margin of frequencies.

And these pulses are needed with about 2 or 3 amps in 12 volts direct current.

Luckily enough we have in our electronics shops two masterpieces of modern technology; one is the integrated circuit NE 555, a universal oscillator, a timer, and the other is the power transistor 2N3055 (the horse power of direct current when you need up to 15 amps in your circuits).

With these two special components and a few more ordinary items you can build a power pulse generator to drive an ignition car coil and get 20 to 25 thousands volts in your laboratory, always with the respect that high voltages are due.

One battery/12 volt/at least 10 amperes	One protection polarity diode/15 amperes/100 volts or more
One Amp-meter/0 to 10 amps	One LED diode
One 850 ohm resistor	One 2N3055 power transistor
One small 12 volt fan for cooling the heat-sink transistor	One 100 ohm/1 watt resistor
One Integrated Circuit NE555	One 1uF/25 volt capacitor
Two small switches	Two 1,000 ohm resistors
One 22,000 ohm potentiometer	Cables, bolts, nuts, and solder. All these useful items we have by our workbench.
One 100uF/25 volt capacitor

This piece of equipment is really a high voltage transformer. It was taken from the Physic's Laboratory to the automobile industry in order to get electric sparks into the gas engine cylinders to ignite the mixture of gas and air.

As a transformer, what we call the coil, has a primary winding of a few number of enamel copper turns with a low resistivity; about 0.7 or 0.9 ohms and a secondary winding of many thousands turns of copper wire as thin as a hair. If you plug the primary to the 12 volts of a car battery a few amps run instantly creating and intense magnetic field in a nucleus around which these two coils are wound. The result is high voltage and a spark... mind your fingers! So we need a switch to feed this coil with power electric pulses; the same as it happens in the engine car.

That is the function of the power pulse generator. This unit sources a continuous flow of pulses with a frequency in the region of sound frequencies.

The circuit for this generator is quite simple and you can find similar circuits in electronic books and on the web.

The heart of the unit is the integrated NE 555 made by Fairchild, though it appears with others denominations by different manufacturers. So it is found like XR-555, SE555, LC555, and LM555. There are even two units into the same capsule with the 556 figures.

About the power transistor 2N3055...There is plenty of information on the web, being its main characteristic that it can manage easily up to 15 amps, always running in the region of low voltages...nevertheless something has to be taken into consideration. This circuit works with intense currents, and this means heat. The 555 IC delivers in the circuit a current of 75 milliamps to the 2N3055 base and if you touch lightly its capsule, you will notice that it is hot. Nothing convenient for an IC. So I developed a heat-sink taken from a piece of aluminium, bending it in the shape of a V and gluing this metallic piece to the upper part of the NE555 IC capsule.

Other source of heat in the circuit is the protection polarity diode. I made a heat-sink for this diode by cutting part of a small heat-sink from a discarded CPU computer, and used the fan for cooling the whole pulse generator. Through this protection diode the whole current to the circuit flows.Finally it it is important to refrigerate the 2N3055 transistor. I build a heat-sink for this transistor with two pieces of aluminium in the L shape joining both with screws. The 2N3055 has the capsule as collector, so you need to isolate the capsule from any other metallic part in the cabinet. Use a mica wafer and silicon grease. For increasing the cooling capacity of this heat-sink, I fixed the L pieces to the bottom of the metallic cabinet.

To be sure that the power pulse generator doesn't turn into an oven, I added a small fan from the above mention CPU and also open some holes in the bottom and in one of the lateral cabinet sides.

Never change the polarity of one of these small motors, they are DC motors with its electronic circuit into the rotor (the piece that turns) made from SMD components. There is a transistor inside which gets destroyed instantly if the polarity is changed when you want to invert the rotation of the fan. Better change upside down the fan itself.

To control the current pulses reaching the primary of the high voltage coil we need an ammeter. An expensive instrument for a hobby economy. That is why I recurred to an old time milliammeter I found among the stock of my components bank. After testing this milliammeter against a DMM and checking that its measurements were acceptable I decided to use it as an ammeter in the unit frontal panel. The movement reaches only 5 milliamps and I needed to measure up to 10 amps.

The solution was to short-circuit the binding post of the instrument with a heavy shunt made with constantane wire by the error and trial method.

After a few trials I encounter the right wire length to make the needle reaching the 5 milliamps when the total current in the circuit is of 10 amps. So any measure in this instrument has to be multiplied by a factor of 2.

In the front panel you find also a switch that allows selecting a high or a low frequency. With low frequencies you can drive 12 volts lamps in a flashing mode, always watching that the current be inferior to the 10 amps. The high frequencies are mainly for driving car ignition coils searching the most appropriated to a particular coil with the frequency control knob. You find also the ON/OFF switch and the pilot led.

Experiments in high voltage at a home laboratory, I understand, must be made WITHOUT any kind of connection to the main line for many reasons. The personal security is the most important, but there is another one that has to be minded: high voltage sparks produces electromagnetic waves, and in a connection to the home power line, the mains, these electromagnetic waves propagates to all the neighbourhood interfering with TV sets, computers, electro-medical equipment, radios, etc. This electromagnetic energy liberated by high voltage sparks is harmful to any electronic equipment...even yours.

Your experiments must be short in time and only run to show briefly what you are looking for. It is advisable to investigate the mysteries of high voltage far from your electronic equipment...such as computers, power sources, amplifiers, video cameras.

Don't forget that in many countries you can even infringe the law because of the electromagnetic energy these high voltage devices radiate. So using a BATTERY is a more secure and comfortable way of conducting high voltage experiments at your workbench, though there is the problem that the small batteries we use in a home electronic lab have reduced capacity...mine is only 4,5 amps . Though if you are installing your equipment in your garage or cellar and own a 45 amp battery...congratulate yourself. Not all of us are so lucky. Nevertheless, with a small battery many experiments can be driven comfortably providing you have means to recharging.

You can make a spark gap easily with a spherical metallic drawer knob and a big needle. Two brackets of any isolating material can support these two pieces...one in front of the other, being also necessary to develop a way of changing the distance between the needle an the metal sphere to adjust the gap.

Building a spark gap solidly allows you to get an idea about the voltage your generator is able to get. More or less each millimetre space between the needle tip and the sphere is equivalent to 1000 volts tension. This is not a rule...there are many factors involved such as temperature, humidity, barometric pressure of air, ionization. But at home, to measure high voltages is really difficult; if not impossible. Though never, never intend to measure high voltages with your DVM.

Once you have the spark gap plugged to the coil and a stream of sparks are running for a few seconds, you will perceive a peculiar smell; it is the ozone gas. Precisely this chemical element was discovered experimenting with electric sparks into the oxygen. The chemist was Van Marum, from Holland, in the year 1785, who first reported this effect of high voltage sparks.

The spark gap is also a source of strong sound. It is a rattling sound which frequency depends from the frequency of the power pulse generator. At the higher frequencies this sound becomes a hissing whistle and from the needle tip you will not observe sparks but a stream of light surrounding only the tip. If your spark gap shows all these manifestations, your job has been successful and you are ready to enter in the fascinating field of high voltage experiments. Do please read my safety precautions below !

* Always turn off the energy to the pulse generator and to the high voltage coil before manipulating into this equipment. Be sure that the power is off.

* Do not touch any part of the spark gap with metallic objects, screw drives or similar, and do not approach your fingers to the spark gap, when working. Sparks can jump even at a distance about one inch (25 millimetres)

*Do not forget that electric sparks jumping into the air generate ozone, an irrespirable gas.

*To operate this equipment with a sophisticated power source can damage the source

*Also any other electronic equipment, such as computers, digital photo cameras, oscilloscopes, TV sets, radios etc., near the high voltage coil can also be damaged.

*And finally, please, do not forget that when working, the high voltage coil is an electromagnetic wave transmitter, which can be heard by RF receivers around your neighbourhood.

Having all this in mind, I wish you successful experiments studying the intriguing world of high voltage.