X-ray transformer 60 kV
Above left photo shows the transformer which has everything under oil including rectifiers. The right photo shows the face plate specifications.
Above shows the series of 4 photos of the spark initially jumping just over 1 inch to my 200 kOhm water resistor for current limiting. The yellow ruler is 9 inches. The second photo shows the spark jumping to the sheet metal back that I has too close. It then began to "climb" and stretch out. This is now the full output with no resistor. It reaches it's full height at 26 inches before extinguishing like a Jacobs ladder. My wife came out to see why the power had "browned out" in the house.
Input power for the spark through the resistor is 25 A measured by a clamp meter at perhaps 100V. I didn't take current measurements with the spark above but the input voltage was set on the variac at 200 V. It didn't trip a 20A breaker possibly because each run was only a couple of seconds.
The mobile unit partially disassembled. I have already used the meter to make my high voltage meter described later. One of the ballast transformers went on to be used as the electromagnet in my magnetic levitation unit.
A peek at the internals lifted out of oil. The transformer which by my calculations will be at least 17 kV AC in a single winding drives a bridge doubler arrangement with 2 diodes. The 2 diodes are the single black bar in the middle photo about 1 foot (30 cm) long. The right photo shows one terminal of the capacitor which is about a cubic foot and occupies most of the space.
The burnout on the left above lost only 4 of the 67 resistors. It was resurrected and extended to 100 resistors for total 160 kohm and immersed in oil in the container above. Despite the 6 inch gap between electrodes it still arcs across at times with this 100kv supply.
A 5 inch (12cm) arc between terminals is on the left instead of going through the resistor as intended. On the right with the upgraded resistor with a large convoluted power arc that last about 1/2 second.
The left photo is of my poorly designed ceramic capacitor bank cut in half with the blown capacitors removed. I blew out 40 out of the 200 capacitors before I got a satisfactory photo. Of course this is very stressful for capacitors. The right photo is the same diode setup but with my rolled polyethylene/aluminium foil capacitors of 48 nF and 15 nF giving a much more intense spark with some steel wool to give the sparkles.
The circuit diagram is shown above. One diode was made from 3 microwave oven diodes rated around 11 kV each and the other diode from two 1N4007 (1000 PIV rating) arrays of 40 diodes each.
Here is a low voltage dual 5 stage C-W multiplier which puts out 2000 VDC from 100 VAC. The current is very low at the highest voltages and even the digital multimeter drops the voltage by perhaps 10% or so.
Voltage multiplier (Cockcroft-Walton)
At this stage I am a little unclear whether I will make it a mains frequency unit run from an x-ray transformer or a high frequency driven unit. The capacitor sizes are vastly different but I can get more convenient power from the x-ray transformer.
This is a 240 V / 3 kV transformer rated at 10 kVA which cost AUD$50 at a junkyard. Tested here using the most modern equipment with a draw-an-arc-off-it-and-see approach. I used the ballast as described in Scitech to limit the short circuit current to around 15 A. It takes 2 strong people to lift it, so at the moment it is stuck on top of my arc welder and 'will not be moved'. It makes a useful anvil as well.
coil sparks 60 kV 2004
Alternatively one can use SIDAC's. This very simple circuit uses the transformer, capacitor and diode out of a microwave oven to supply 2000 VDC. Once the voltage rises to 2000 V the SIDAC's fire dumping the energy into two ignition coils to give sparks of easily 5 cm. I am using 9 SIDAC's each rated at 240 V 1 A RMS and 20 A pulse. Each is shunted with a 1 Mohm resistor to give more even voltage division. There is a 10 Kohm 10 W resistor used for these shots but power draw is triggering a 10A cutout and there is sufficient heating of resistor, diode and SIDAC's to only allow short runs. 50 Kohm will allow about 4 sparks per second.
Unfortunately this is very hard on the ignition coil's insulation. I have lost one coil but the remaining one still puts out 3 inches and also about 10 inches of surface tracking (below).
in a MO 60 kV AC.
(Microwave oven transformer) 2004
In good Tesla Downunder tradition, total cost is almost nothing, being made almost entirely from scrap microwave ovens, old ignition coils and only a handful of new parts such as the SIDAC's.
supply 13 kV DC 2005, 2008
The left photo shows a lash up of the charger, showing the various basic components including a red warning strobe to show it is charged. The right photo shows the partly built charger and 6 kV spark output is shown (drops to less than 1 kV once arc starts). To keep the HV and mains isolated and still feedback the voltage, I send pulses into a ferrite rod which will be picked up and trigger the solid state relay to turn off once the voltage has risen to the desired level.
I have rewired this supply with an extra stage for higher voltage and added some big power resistors. This is to be used for charging my big capacitor bank.
The photo above shows the latest reincarnation of this supply. Now with extra stages to boost to the 13 kV shown here plus the addition of two 50 kOhm 100 W resistors as current limiting. This is to handle the higher voltage of my big cap bank.
This is based on a TV flyback coil and a single 2N3055 power transistor and other on-hand components giving a 1/2 inch spark at 20 V 3 A input. It runs at frequencies above the audible range and only under load is it heard as a whine when the frequency drops. This is one of my earliest HV setups but not particularly efficient.
This circuit is from Andrineri from Vladimiro Maziili. The supply is
made almost entirely from parts from a scrap microwave ovens which are of
the electronic type (the light ones). I used 2 IGBT's and one of the heatsinks along with the small toroid inductor.
The main ferrite transformer, also from the microwave, had the primary heavy
Litz wire removed and replaced by 10 turns centre tapped driven by the
simple Royer type circuit. I have also removed the spacers between the
cores. Non microwave parts included the main capacitor, two 12 V Zener's, a few resistors and two high speed diodes (BYV-29
500 Volt, 9 A, 60 nS).
The left photo is from a modern TV flyback transformer with core spacers removed and the exposed core wound with 10 turns centre-tapped of rather flimsy wire running about 250 W. On the right is an older but larger one.
The older style flyback transformer here has the spacers removed and is a little more efficient. It is running at 44 kHz at 30 V, 6.3 A. (The meters are lying). The right photo shows a 1 inch DC arc with a 30 nF 40 kV cap added to the unit which now has a dedicated 37 V 10 A power supply. The intense spark is seen behind the filter made out of 2 welding goggle filters.
TV flyback HV supply 80kV DC 2005
The left photo shows it running with 4 inch sparks with limiting provided by several resistors. The right photo shows the corona in a time exposure.
frequency flyback supply 4 kV AC 2007
I used a simple circuit with a 555 oscillator driving a MOSFET. This drives a ferrite transformer which was from a microwave oven inverter power supply and puts out about 2 kV. Not technically a flyback transformer but similar. I rewound the primary to 10 turns. Once driven by enough voltage (about 37 VDC) it puts out about 900 VAC RMS into the capacitative load. This is about 20 W or more even with no additional load. Since the input waveform is a switched half wave, it has a lot of harmonics. This excites the resonance of the capacitor and the coil at perhaps 200 kHz. I have smoothed the output by using a resistor. Because this is near resonance the resistor takes a lot of the output and the 4 x 10 W resistors get to 160 C.
The setup is housed in an old variac case which is a neat case and has room for the transformers. The load resistors are shown and also a voltage divider to allow a CRO to be hooked up.
The spark at 22 kHz is about 5 kV peak (left photo) and can be drawn out. Voltage at 100kHz is about 900 VAC RMS, lower(center photo), but still enough to draw an arc and heat wires. It lights a nearby neon as well (right photo). And, no, those low voltage terminals don't stand up to 5kV long.
Left photo is at 22 kHz, center photo at 70 kHz and the right photo is at 100 kHz. The smoothed resonant effect is evident at 100 kHz where the waveform is much more sine wave like.
I learned a bit making this which will be helpful in making solid state Tesla coils in the future. During the course of testing I did convert this to a half bridge supply before I realized I could smooth the waveform resistively. I have let the smoke out of a few IGBT's and MOSFET's during testing.
Candy box HV 40 kV
The disposable photoflash unit with the electronics removed shown charged by the 1.5 V battery.
The completed box which produces a 1.5 inch spark with a repetition rate of about 2 Hz. It is "safe" to touch giving a mild pinprick sensation. This formed one part of my display at a University Expo recently where I was offering "free" electric shocks. I would demonstrate on my arm first before calling for volunteers and it was quite a popular display.
This is the waveform of the output at 20 uS per division, which is a damped wave of around 25 kHz with a superimposed signal of about 1 MHz on top. It is about 40 kV at 20 uA but measurements are difficult at this frequency.
HV supplies from a photocopier 5 kV 2006
The left photo shows the larger supply outputs 5 kV DC, 3.8 kV AC and
a few smaller voltages.
Valve regulated supply
50 kV AC 2006
Xenon lamp ignition
50 kV AC 2008
The sparks here are about 1 inch and you can see the multiply stacked gap firing as well.
This is the internals of a Siemens 120kV x-ray tube head which includes the transformer (not rectified) and a rotating anode under oil sealed and lead shielded. The glass has been removed with the outline shown in yellow. The electron beam is shown in red and the x-rays in purple. The induction motor is outside the glass and works well on 250V with a phase delay with a 1 uF capacitor on the additional windings. The right picture is the filament on the cathode electron gun which I have joined to some glass feed through wire from a neon tube.
Unfortunately the HV winding was open circuit but still gave a 1 inch spark at 100V. I sort of hoped it might do better when I got it under oil but of course it didn't. It was drawing about 5kW to get that 1 inch spark!
The 3 second photographic exposure above shows 1 inch sparks from this project. Here's what you need.
The left photo shows the wiring layout. The switch (equivalent of the "points" in an ignition system) is the two wires at bottom right. To operate, touch the two wires together. You should see a very small spark where the wires touch. Current is now flowing into the coil and has built up an internal magnetic field. Immediately lift the wire off to break the contact. The collapsing field creates a voltage spike of hundreds of volts which is raised to perhaps 30,000 volts at the output. You will see another spark where the wires were touching, larger this time. In most cases you will see a long high voltage spark from the aluminum foil to one of the terminals. The right photo show a 2 second exposure with several long sparks.
So you have completed it and have made some sparks. But is it safe? Yes and no. A shock from this to is similar to being pricked with a needle. Not pleasant but tolerable. Of course if you jump backward and trip over and hit your head then yes you may do some injury.
Here is a spark onto my arm. I had to turn on the camera remote and turn on the sparks with my left hand, seen only as a blur in this 2 second exposure. It took about 10 shocks to get a reasonable picture. My right arm receiving the shock will jump involuntarily. That's how muscles work and was discovered by Galvani giving shocks to frog legs. Anyway, I survived unscathed although I probably get more practice than most.
So what can you do with it?
How about lighting up a lot of "dead" fluorescent lights? As you can see, some are more dead than others. Try testing conductivity of various objects like dry then wet wood or plastic. See how well it jumps through paper then thin plastic.
Just a note. High voltage can damage electronic equipment like phones, ipods, TV's and computers. Keep it well away. 30,000 volts will jump 1 inch and 2-3 inches along the surface of insulation.
If you want to progress further to something a little more complicated, try
The top photo shows the ignition coil and relay running on 12 volts at 5 amps from a power supply, battery charger or car battery. There are only three parts. It uses a relay as a vibrator to turn current on and off rapidly to an ignition coil. The bottom left photo shows a close up of the wiring. The bottom right photo shows the schematic with the capacitor, relay and ignition coil.
The left photo shows the relay with the connection for the coil as
the bottom two pins and the other contacts coming out in line. Note the
center contact is the one that moves and touches the lower contact in this
picture. This is the "normally connected" (NC) pole and is the one used
here. The top contact is the "normally open" (NO) pole and is not used here. The right photo
shows the ignition coil. These should be available for a few dollars
from an auto wreckers.
Photo shows the identical circuit running 2 coils in 1972.
This is a static electricity generator of the type used in displays which make your hair stand on end. It uses 2 inch rubber belt with fibre reinforcing which was the only non black belt I could find (black rubber is slightly conductive). Powered by a variable speed electric drill. Top load is 12 inch ducting. I have tried a 10 kV DC charging spray but there was no improvement over the standard triboelectric static generation. Maximum sparks on a low humidity day are about 2 inches. More work needs to be done. Winter and the increased humidity will put this on the back burner for a while. PVC is not ideal as it does tend to absorb a little moisture and polypropylene is better.
The left photo shows the spiral impulse generator generating a 5 mm spark (perhaps 5 kV) from a 1 mm spark gap. The spark gap is between the two electrodes (which are not connected to each other) and the right upper electrode is the one that continues through to the output electrode strip with the longer spark coming off it. The capacitance between the two strips is 900 pF. The right photo shows the 2 kV peak input from a small NST limited by a variac. It is half wave rectified and run through a 1 MOhm resistor. My meter reads peak voltage AC or DC as I have designed it.
The left diagram shows the circuit of the basic spiral impulse generator with two copper strips with a spark gap between them. The are insulated from each other and rolled up. The right diagram shows the version I am using with extended foil. The larger version I try later has equal foils and works better for a number of reasons.
The left photo shows the 1984 patent that this comes from. The center photo shows the start of the copper strip windings separated by polyethylene sheet. The right photo shows the strips of copper foil of 10 x 62 mm obtained as big sheets of 60 cm square from a craft shop. I have soldered two together for the long winding. Hence there are two parallel strips of 4.5 turns and one strip only continues on for another 4.5 turns. It doesn't seem too efficient but I don't really understand the setup enough to know which way to modify it best. I imagine that I could make one with more turns to start.
The photo above shows an earlier version that didn't work other than to light a neon pilot. No real idea why, but I tried again with thinner flatter windings.
Now here is a better one.
The photo above shows a beefier version. Specifications:
LED Voltmeter 2008
Above shows the meter reading 13.06 kV using a 30 kV rated HV probe. The leads and switch are at the back. There is some rudimentary HV protection using a neon pilot globe, capacitor and a small toroidal coil in the main lead.
Water resistor 2008
The left photo above shows the ends of the 2 m x 10mm tubing with copper tubing connectors and valve to allow air release or to replace the water if it becomes clouded or for a resistance change. The advantage of this construction is that it is not specifically inductive so sparks, like Tesla sparks will not try to jump across adjacent windings. The right photo shows sparks from a 60 kV supply. The resistor was set at 200 kOhms. The heat was enough to cause cavitation either with boiling or electrolysis but it survived fine without leaks.
A DRSSTC (Double Resonant Solid State Tesla Coil) is a must do at some stage.
Lots of diodes: A 6 foot stack of 112 of 2.5 kV 2.5 A, 200 of BYV-29 500 Volt, 9 A, 60 nS, 500 of IN4007 1000 V 1 A, 1000 of 2.5 kV, 250mA, plus 2 of 1200 V 1700 A SCR's and another 12 similar sized ones. Lots of projects in mind for these.
Marx generator for high voltage DC which means more capacitors (a lot more). I have a large number of resistors that should do in HV service and am getting some ceramic capacitors which should be OK for over 1 foot of spark.
I have various IGBT bricks and arrays to use in a half or full bridge arrangement to experiment with and also 20 A IGBT's from old microwave ovens.
A nice 60 kV transformer and heavy dual variac for the kids to play with.
This page was last updated September 12, 2010