High Voltage
Home
Tesla coils
High Voltage
Pulse Power
Electronics
Rail gun
Lasers
Magnetic Levitation
Nuclear, X-ray
Public Displays
Misc
Links
About Me

 

 

 

 

STOP PRESS  This is my old site last updated June 2005.  Enjoy the pics here but it is best to shift direct to the new site. Looks the same but lots more stuff and regularly updated.  The full size pictures  are only available there.

CLICK HERE to go to tesladownunder.com index page


High voltage projects on this page include:

bullet

100 kV DC (dental x-ray unit)

bullet

100 kV DC (mobile x-ray unit)

bullet

Voltage multiplier (Cockcroft-Walton)

bullet

Jacobs ladder

bullet

Junkyard transformer

bullet

Ignition coil sparks

bullet

MOT supply in a MO

bullet

TV flyback HV supply (60 W)

bullet

TV flyback HV supply (300 W)

bullet

Strange HV/water effects

bullet

Van de Graaff generator

bullet

Voltmeter

bullet

Future plans.

High voltage projects on a separate sub-page include:

bullet

Lifters 

bullet

Lifters 1 Beginners

bullet

Lifters Better

bullet

Lifters Now on permanent display in a science museum.

 

100kV DC  (dental x-ray unit) from a small x-ray transformer.  This was given to me by a friend who got it for AUD$1 on eBay (Thanks, Ralph). It is from an old dental x-ray machine and is rated at 60 kV. It looks tiny for a mains transformer to give this even under oil. It doesn't have any shunts and can draw 15A from 240V.  I connected it up and with about half power (125 V) it puts out about 30 kV at 20 mA before internal shorting occurs and the oil starts to bubble. Occasionally it will run to a 2 1/2 inch spark on the full 240V.  It has a lot more power than an NST. 

      (video 570 k - run mouse over)

Above left is the 60 kV transformer with a bit of suppression circuitry (ex microwave).  The video shows the transformer under oil in a PVC pipe running as a Jacob's ladder with a drink can next to it for scale.  A Jacobs ladder is a spark gap in which a spark forms initially between the lowest and closest points then rises as the plasma heated air rises.  It eventually extinguishes near the top then restarts at the bottom. A favourite backdrop for old Frankenstein movies.

To obtain around 100 kV DC from this 60 kV x-ray transformer I input 150 V AC which gives 36 kV AC out.  With a  diode and a 0.015 uF 80 kV mica capacitor connected as a voltage doubler, around 100 kV DC is achieved giving a best spark of 5 inches (13 cm).    Note the spark is hazy (and fairly quiet) due to current limiting with a resistor and an inductor to reduce strain on the capacitor.   The whole setup crackles with corona when in action.

  (click to enlarge)

The spark above is attenuated with a resistor (below right and the short central poly tube in the left photo) which has 67 x 1.8 k ohm resistors and is almost exactly 100 k ohm.  The voltage rating is unknown but for these 2 or 3 watt types is probably around 1 kV each. It was placed in a PVC pipe and filled with paraffin wax.  I have had these in my junk box for around 20 years so I hope they aren't past their use-by date.

  (click to enlarge)

The capacitor (the upright tube in the photo) is a 2.2 nF rolled polyethylene in oil cap composed of 2 sections with 8 layers of sheet in each side.  I have a 1 3/4 inch (4 cm) safety gap which only starts to fire at output sparks with the voltage doubler of 4 inches (10 cm). This was replaced with the mica caps for the highest voltages.

(click to enlarge)

The diode is composed of 290 x 1N4007's in a PVC pipe about 15 inches (40 cm) long. Each one is rated at 1000 PIV at 1 A.  This was designed to accommodate the full 60 kV AC = 169 kV peak to peak. Allowing for 10% increased voltage from the variac gives a total 186 kV which allows 50% headroom only.  Note no dropping resistors were used.  So far no problems (but many lesser ones have come to grief). I now have two of these to allow another stage to my voltage multiplier.

I also have an inductor made from 21 g wire close wound 15 inches on a 1 inch (2.5cm) former.   The inductor and resistor are needed to limit the current for devices such as the lifter (below).

100 kV (mobile x-ray unit).
I have acquired a mobile x ray unit base with its associated 100 kV transformer, diodes and capacitor under oil.

    (click to enlarge)

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.


  (click to enlarge)

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.

(click to enlarge)

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.

  (click to enlarge)

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.

For my 125 kV x-ray transformer head internals see here.

 Voltage multiplier (Cockcroft-Walton)
This uses two diodes and two capacitors to convert an NST's 12 kV AC into around 30 kV DC. This gives an intense spark 1 1/2 inches long.

  (click to enlarge)

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.  The lack of equalizing resistors is probably the fatal flaw.  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.

(click to enlarge)

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.

 
Jacobs ladder

  (click to enlarge)

This one is powered by my original old unpotted NST and shielded with acrylic tube to allow safe public display.  This was struck by my TC resulting in mains arc-over in the power switch and fuse and also destruction of the limiting resistors for the indicator neon's.  I need a bigger shed.

Junkyard transformer

  (click to enlarge)

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.

Ignition coil sparks  A simple way to drive two ignition coils is with a light dimmer in series with the 250 VAC mains and a capacitor of perhaps 1 - 10 uF.  I used two microwave oven caps in parallel for about 2 uF at 2000V which gave sparks of about 2 inches (5 cm).  My meter says about 60 kV peak but may be over reading a bit.

(click to enlarge)

Alternatively one can use SIDAC's. This very simple circuit uses the transformer, capacitor and diode out of a microwave oven to supply 2000VDC. Once the voltage rises to 2000V the SIDAC's fire dumping the energy into two ignition coils to give sparks of easily 5cm. I am using 9 SIDAC's each rated at 240V 1A 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. 

(click to enlarge)

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).

  (click to enlarge)

MOT supply in a MO.  (Microwave oven transformer)
I have a couple of MOT projects. Firstly, there is the SIDAC driven ignition coil driver above.  Secondly there is my MOT multiplier originally constructed as a HeNe laser supply which gives about 9kV firing and 2kV running, ballasted by 30kohms.  I have never had any problems with this supply which gets used for all sorts of general HV stuff in the range 1 - 9kV such as nitrogen lasers.

To accommodate these projects, so that they look less out of place in a modern kitchen, I rewired a microwave oven, keeping the existing safety interlock, light, fan and transformer.  I removed the magnetron and old electronics and wiring.  I then cut a hole in the cooking cavity and outer case with an angle grinder, added terminals and presto, a neat HV supply. The HV lead from the transformer passes through the microwave waveguide to the cooking cavity with the wire in plastic tubing for extra insulation.  The fan helps cool things and the safety interlock turns off the power when the door is open.  (I forgot about this and thought I had blown a fuse).  There is room for both projects. 


(click to enlarge)

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.

 TV flyback HV supply 60W

(click to enlarge)

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.

TV flyback HV supply 300W

(click to enlarge)

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 input here is about 30V 10A (300W) with resonance at about 70 kHz. The IGBT's are rated at 600V 30 A and only get slightly warm in action but the cap will overheat if the resonant frequency is too high.  Output is probably around 2000 VAC.  The arc stretches out to about an inch and has a lot of power.

(click to enlarge)

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 250W.  On the right is an older but larger one.

(click to enlarge)

 The older style flyback transformer her 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 30nf 40kv cap added to the unit which now has a dedicated 37 V 10A power supply.  The intense spark is seen behind the filter made out of 2 welding goggle filters.

(click to enlarge)

This is a standard screwdriver.  It is interesting how the arc bends around it.  This is because the hot arc channel is a low resistance but the air just next to the screwdriver is cold (or at least not not ionised and would have to be "jumped" by a sufficient voltage for it to connect. This only happens with stable pulsed DC or AC arcs.  One could make up a bit of a pseudo-explanation for this and indeed I have on the 4HV community.

Strange HV/water effects  While I was waiting for my deionised water to freeze around my coinshrinking setup, I thought I would do some HV conductivity tests.


(click to enlarge)


Photo above left, shows the effect of an electrode with 4kv DC across it when dipped in the water. It creates a spike from the mutual attraction of opposite charges. Almost ferrofluid like. The yellow tip is a reflection of the yellow base which is my theme background colour in most of my photos. This spike is stable although there is a moderate water flow around it.  Wire width is 0.09 inch (2.2mm).  As the deionised water became conductive enough to sustain a higher current , the faint and feeble spark increased to a power arc to water of about 2kV DC eventually to the point of making the wire red hot.  Centre and right photo's.  In contrast, the water is dimpled downwards beneath the arc.


(click to enlarge)

This shows DC sparks from my flyback supply with a 0.2 uF capacitor providing a spark energy of perhaps 10 joules at 10 kV.  In air this spark will jump less than 1/2 inch (1.25 cm) but surface tracking means that this will be many times longer and gives a widely branching long spark suggesting a much higher voltage. The left photo above shows a single discharge and the centre photo is a time lapse shot of multiple shots.  The right photo shows a spark direct to the other electrode about 4 inches away which discharges the full 10 joules with a big bang.  Picture scale is about 3 inches (7.5 cm) across.

Van de Graaff generator

  (click to enlarge)

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.

Voltmeter  Using the meter from my old x-ray unit (with a dial reading of 100 kV full scale deflection - FSD for 125 uA), I added a resistor chain (720 M Ohm, 72 M Ohm, 7.2 M Ohm, 800 K Ohm) to allow FSD of 100 kV, 10 kV or 1 kV.  The current is full wave rectified at about 100V level with fast diodes (BYV-29   500 Volt, 9 A, 60nS) and is protected by a gas arrester and diodes across the meter itself.  A capacitor smoothes the output of the bridge rectifier giving the ability to read DC and peak AC. Voltages up to 1000 V agree with my digital voltmeter to within around 5% on DC and peak AC 50 Hz.  A 30 kV power supply seems to read accurately.  This is not intended for Tesla type frequencies but it is reasonably non inductive and the diodes are high speed ones.  A capacitor divider is needed as well for higher frequencies. All the main workings are behind the acrylic to avoid accidents.  Although the resistors have a peak rating of around 100 kV, the spacing between strings is not enough for more than 80 kV before big sparks start jumping everywhere although without damage to the meter..


 (click to enlarge)

Future plans

bullet

An SSTC (solid state Tesla coil).  My printed circuit board has arrived from the Captain, for an audio modulated 3 kW SSTC  using MOSFET's such as  IXFN3650. Now I need to find the parts.  Alternatively, the new DRSSTC's with resonant primaries are now reaching 10 feet sparks.

bullet

  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.  Lots of projects in mind for these.

bullet

Marx generator for high voltage DC which means more capacitors (a lot more).  I am planning for a 2 stage Marx to boost my 100 kV to 200 kV using water resistors and doorknob caps.  I have the caps, tubing and water (deionised) but have to assemble it.

bullet

I have an IGBT array to use in a half or full bridge arrangement to experiment with and also 20 A IGBT's from old microwave ovens.

Sadly I also have to eat, sleep, work and communicate with my family periodically...
 

This page was last updated August 28, 2005