This article is very old, from around 2007. It was originally published on my old website, flylab.ovh.org, now defunct. It’s unlikely to have much educational value. I’ve republished it mainly for sentimental reasons. Grammar and style were left “as is”.
Introduction
I’d describe the High Voltage Generator (HVGen 2.0) I have built using two ignition coils from scratch. You can do some interesting experiments and demonstrations using this device.
Construction
The HVGen consists of 3 main parts: a signal generator, a high voltage block and a power supply.
List of components
| Part | Description |
|---|---|
| Two car ignition coils | The coils should be identical, but it’s not necessary. But they have to have exactly the same primary winding resistance. |
| Power MOSFET transistor | It should have the drain-source resistance RDSon possibly low, high power and UDSmax more than 600 V. I’ve used IRF740. |
| CMOS 4011 | |
| 2x standard low power diode | For example popular 1N4148. |
| Resistors | 2x 4.7 kΩ and 1x 10 kΩ. |
| Capacitors | 1x 68 nF, 2x 100 nF, electrolytic 6800 μF 50 V and 470 μF 16 V. |
| Rectifier bridge 20 A | |
| Supply transformer 24 V 100 W | I used a safety transformer 230 V -> 24 V. |
| Stabilized power supply 5-12 V | Needed to supply the signal generator. |
| Other stuff | Like PC board, wires, insulating tape, a case etc. |
Schematic
The schematic is shown below:
The coils are connected in anti-phase parallel configuration, so the voltage between HV connections is 2 times higher than in the case of using single coil. The supply voltage is also higher than in the first version. Now it’s 24 VAC, so U = 33 V.
Signal generator
This circuit can be assembled on the universal PC board. Potentiometers and R2 and R4 should be linear. They are used to adjust the frequency and inlay. To protect the generator against EMP it should be about 20 cm away from coils and transistor or be inserted in metal grounded box. It’s supplied from its own 5 V supply. I used also other generator, NE555 powered.
Keying transistor
The power MOSFET transistor with possibly low drain-source resistance RDSon, high power and UDSmax more than 600 V. The back EMF may destroy it if it was a low-voltage one. I’ve used very good IRF740 with a big radiator. After a few minutes of work it’s fairly hot. If the RDSon is low, the transistor won’t be very hot.
Ignition coils
You need two car ignition coils with resistance 1.5-4 Ω, like shown below on the photos (identical ones are the best, or course). They must have exactly the same primary winding resistance.
Assembly
At first, you should check the signal generator. Connect it to the power supply, then to small speaker or phones. You’ll hear the sound. You can also use an oscilloscope.
The circuit power supply-transistor-coils should be made of thick wire Φ1 mm. I made a rack of polyurethane for it. It looks like ‘I’. On the top there are HV connections. You can see it in the photos in the Introduction section.
HV connections should be made of special HV cable (used in TVs or ignition installations). In my own construction I haven’t done it, because they are short and distanced from other elements. On the top there are two screws. Insulate carefully these connections, because some sparks may appear on the surface of the plastic.
Experiments
Here are some experiments I did using this device. They look more impressively in the dark. In darkness, you might accidentally touch a HV element, so be careful.
Electric spark
The simplest experiment. You need two thick wires with sharpened endings. Screw them in terminal. They should be 2 cm from each other. If you turn the device on, you’ll see a continuous spark between them. Try to check, what is the maximal distance the spark still appears. In my device, there is 4 cm.
Jacob’s ladder
A Jacob’s ladder is a device consists of two electrodes looking like V and a HV power supply. The simple explanation is that an arc starts at the bottom and due to the fact that hot air rises, tends to move up the diverging rods until they are too far apart for the voltage provided by the power source.
My own version consist of two 50 cm cooper wires. It’s 44 cm high. The electrodes distance in the bottom - 2 cm, on the top - 3.5 cm. This video shows the working device. It was made by handy; sorry for bad quality.
In the pictures there are many sparks, but fairly there’s only one. The generator works in pulses and the spark in each time in other place.
Kirlian photography
I’ve experimented with a simple kirlian camera, but I didn’t obtain good effects. Some photos above.
Sparks inside the light bulb
A very good-looking effect is to wind some cooper wire on the light bulb and connect it to generator’s one terminal, the base to another one. There are nice sparks inside the bulb. I used 200 W one and a wire Φ0.2 mm. The device worked only a few seconds and the bulb broke.