A Multi-purpose power pulse generator capable of driving Tesla Coils and other high power coils. This device is based on the Homemade Tesla Coil project and uses an improved version of the ignition coil driver circuit to generate high voltages.
This unit quite simply can generate high current pulses of variable frequency and pulse width. This unit uses the Square wave frequency generator shown in the DIY Devices section for the main signal source but any other signal source can also be connected to it. The input signal is amplified using an array of nine 2N3055 power transistors (T2) which is capable of switching huge amounts of power.
|WARNING: High Voltage is used in this project!|
A switch allows power to be sent to external coils for low voltage applications, or the internal ignition coils can be powered for charging a large HV pulse discharge capacitor.
The low voltage circuit in this device is similar to the driver for the Homemade Tesla Coil, but with some important differences. The high current pulses from the Lead Acid Batteries makes the signal generator unstable in the original design. The new version uses a completely independent signal source with its own battery to minimize the interference. There is also an extra buffer circuit to protect the 2N3055 Transistors from voltage spikes caused by the inductive kickback from the auto ignition coils.
All the power electronics are housed in an Aluminum case finished with panel meters, IO ports, and switches. The signal generator circuit is housed in an independent unit with its own 9V battery. This can be connected to the main unit via a shielded cable allowing it to be operated from a safe distance.
The high voltage output from the ignition coils is rectified using some large high voltage diodes (D2) designed for X-Ray machines. The rectified output is connected to a large capacitor (C1) for smoothing the DC output. From the smoothing capacitor an inductor (L1) and an additional ‘de-Q-ing’ diode (D3) have been added to the charging circuit to block the AC ringing from the TC primary coil from reaching the the smoothing capacitor. These also help to protect the the rectifier from short circuits, arcing currents and possible back EMF or transients.
|SW1||Low Voltage Selection Switch|
|TR1||Four Ignition Coils in Parallel|
|T1||BFY 51 Transistor (Preamplifier)|
|T2||2n3055 (nine in parallel)|
|D1||High Power Diode|
|D2||High Voltage Rectifier|
|C1||High Voltage Smoothing Capacitor|
|C2||Pulse Discharge Tank Capacitor|
|SG1||Variable Spark Gap|
|The connectors used here are just standard banana types. They are not designed for high voltage use and will therefore leak a little energy by ionising the air nearby.|
The main high voltage front panel on the box has sockets for HV DC output, an internal HV pulse discharge capacitor, and an internal spark gap. This allows the high voltage circuits to be configured in a number of different ways without having to re-wire any internal components.
The image on the right shows how the panel is wired to drive a Tesla Coil. The spark gap can be adjusted using a handle on the side of the case. Depending upon the resonant frequency of the TC being driven, it may be necessary to adjust the capacitance. This can simply be done by adding more capacitors in parallel, or using a separate one.
This image shows the interconnected outputs of the ignition coils. The ignition coils are wired in parallel to give a higher output current.
All the high voltage cabling inside the box is placed inside flexible plastic tubing for added insulation. You can see here that the low voltage connections to the ignition coils are also covered with tubing for added protection.
The case is grounded by connecting a thick wire to a long metal spike driven into the ground. All of the ground connections for the internal circuits are also connected to the case.
Connecting the case to the earth spike is essential when using the device to drive Tesla coils. This is because a Tesla Coil (TC) will generate radio frequency (RF) currents that would otherwise become present throughout the circuit. Without a good RF ground you would probably receive little shocks from the controls when operating a Tesla Coil.
Internal Variable Spark Gap
This new spark gap is made using three spherical electrodes in a high K dielectric casing. The double casing of the spark gap reduces the overall noise and allows the airflow to be doped with other gasses.The anode and cathode are spaced further than the voltage could jump and the third sphere can be moved in and out of the gap via a long glass fibre rod. This allows the spark gap to be adjusted smoothly anywhere between short and open circuit whilst it is active.
A pair of 12V DC brushless fans are installed to improve airflow through the spark gap. This is not to improve quenching, but it will reduce electrode corrosion from Ozone buildup in the spark gap casing. A further filtering capacitor has been added across the fans connectors as this type is sensitive to voltage spikes
The control circuit used for generating the driving signal is made using a 555 based circuit. This circuit can be found on the DIY Devices Page and is titled Signal Generator with Pulse Width Control. This circuit is housed inside a small hand held box with a 9V battery. It can be connected to the Power Pulse Generator by a jack plug on the end of the cable from the unit. You can buy an advanced version of this signal source here.
Different ignition coils or transformers will have different resonant frequencies. Using this circuit allows the Ignition coils to be tuned and driven at their resonant frequency.
External transformers, coils, or solenoids can also be driven at any desired frequency within the range of the 555 timer. The pulse width modulation capabilities of the control circuit are used for power level control for transformers and other coils. This feature also allows large or small DC motors to be powered with variable speed between 0% and 100%. These can also be tuned to their resonant frequency.
This device is capable of powering a multitude of experiments and is great for any researcher experimenting with pulsed power or resonant applications. You can see experiments we have done with Tesla Coils using this device on the Tesla Coil Experiments page.