Pulse Discharge

Home Up Get Your Own Accident Revision 2

 

Shrunken Quarter


If you want one of your own click here

The PDM Machine
(aka "Quarter Shrinker")

QS Complete Front 1.jpg (38763 bytes) 

This picture shows the front of the machine. On the lower left is the HV Power Supply. On the lower right is the control box which houses the control circuitry, low voltage transformer, and air compressor.

QS Complete Right 2.jpg (39615 bytes) QS Complete Rear 2.jpg (39861 bytes) QS Complete Left 1.jpg (31443 bytes)

This shows the right, rear, and left views of the machine. If you look closely you can see the buss bars, safety lockout, trigatron, and discharge resistors,

 

Work Coil

QS Complete Containment 1.jpg (36422 bytes) QS Complete Containment 4.jpg (33502 bytes)

The picture on the left shows a work coil in place and ready for a shot. The second picture shows the results after the shot. If you look closely you can see the shrunken quarter just to the right of the wooden dowel. also note the wire shrapnel all over the inside of the containment.

 

What it does

(This picture was swiped from Ross-O's site)

 

How it Works

The Quarter Shrinker uses a technique called high velocity electromagnetic metal forming, or "Magneforming". This technique was originally developed by the aerospace industry, and has been popularized by Aerovox, Grumman,  and Maxwell.  It involves discharging a high energy capacitor bank through a work coil to generate a very powerful, rapidly changing magnetic field which then interacts with and "forms" the metal to be fabricated. It only works with metals of relatively high conductivity, such as copper or aluminum alloys, although it will work to a more limited extent with sheet steel. 

The large current that's induced into the outer rim of the coin may reach a million amperes or more. Since the initial energy is in the range of 3,500 - 10,000 Joules, the instantaneous power is awesome, and for a brief instant is roughly equal to the electrical power used by the entire city of Chicago. The repulsion forces between the work coil and the coin create a huge radial inward compressive force on the coin that easily overcomes the yield strength of all the metal(s) in the coin, causing it to plastically deform the coin into a much smaller diameter. At the same time, a similar outward radial force literally explodes the work coil.

As the work coil expands, the wire eventually fragments, and pieces of the coil are then forcefully ejected outward with the force of a small bomb. Once the coil disintegrates, any residual magnetic or electrostatic energy remaining in the system is transferred into the resulting ball of blue white plasma that fills the blast shield or is dissipated by bleeder resistors.

(The description above was swiped from Bert Hickman's site)

 

Block Diagram

QS Block Diagram 2.jpg (48932 bytes)

Safety and reliability were primary factors in this design.

 

Schematics

QS Charge Circuit 2.jpg (39965 bytes) QS Fire Circuit 2.jpg (46002 bytes) QS Discharge Circuit 2.jpg (29410 bytes)

These show how things are actually hooked up.

 

Calculations

Pulse Discharge Workbook.xls

This workbook gives energy calculations as they relate to a particular charge voltage. It also provides peak and average power dissipation calculations for the bleeder resistor network. 

 

Construction

 

High Voltage Capacitor Charging Supply

HV_Power_Supply_1.jpg (29824 bytes) HV_Power_Supply_2.jpg (30587 bytes)

This is a 34kv power supply which is designed to charge capacitors at a rate of 1kJ per second. I've limited the controller so it's only capable of 22kv. This will help prevent over volting the capacitor.

 

Trigatron

Trig_clear_end.jpg (19372 bytes) trig_parts.jpg (18990 bytes) Trig_PLUG_END.jpg (21362 bytes)

trigatron6.jpg (16637 bytes) trigatron7.jpg (18204 bytes) trigatron8.jpg (15776 bytes) trigatron10.jpg (18488 bytes)

A Trigatron is a fast acting, high voltage, high current switch which is triggered by a high voltage arc inside of the main body.  This design uses a modified spark plug as the trigger electrode.

 

TRIG_1.jpg (55664 bytes)

 This trigatron is one of two units I hand fabricated. The other unit is installed in Ross-O's PDM machine.

 

TRIG_BASE.JPG (18150 bytes)
This is the prototype trigatron base and bus bar configuration.  The pulse cap was hooked up via the 2ga screw down connectors on the left and the quarter went inside the coil on the right hand side of the photo.  This is the 2nd of 2 units we fabricated.  Turns out that the blast force was much more than we anticipated.

 

P6071036.JPG (59961 bytes) P6071039.JPG (59005 bytes)
Extensive damage was done to the blast plate, wooden base, and 1.25" thick Lexan when the diamond plate containment box was fitted over the quarter shrinking coil and the fire button was pushed!  Regardless, with a little last minute engineering we managed to make this unit hold up for 8 or 9 quarter shots.
    

 

Trigatron Firing Circuit

Trigatron_Fire_Ckt_3.jpg (27625 bytes) Trigatron_Fire_Ckt_2.jpg (29446 bytes)

Trigatron_Fire_Ckt_4.jpg (36887 bytes) Trigatron_Fire_Ckt_6.jpg (30637 bytes) Trigatron_Fire_Ckt_7.jpg (35747 bytes)

Trigatron_Fire_Ckt_8.jpg (26790 bytes) Trigatron_Fire_Ckt_9.jpg (28354 bytes)

This method was recommended by Bert Hickman.  It is simple, inexpensive, and will produce about 1" arcs from either a standard ignition coil or a HEI coil.  The light dimmer can be found at Home Depot or similar stores.

 

Pulse Discharge Capacitor

pulse_cap1.jpg (88234 bytes) pulse_cap_label.jpg (102880 bytes)

This unit is capable of storing and discharging over 67kJ of energy. Shrinking of a quarter takes only 4-9kJ. This is an extremely deadly and deceptive component. Utmost care need to be taken whenever working with or near this capacitor.

 

Main Control Box

QS Main Control Box 1.jpg (25797 bytes) QS Main Control Box 2.jpg (33912 bytes)

This box houses the 240v mains isolation transformer which also provides 120vac to the Trigatron firing circuit. It also contains the power supply control board, charge voltage adjustment, status indicators, air pump, air reservoir, pneumatic switches, and other control circuitry. 

 

 Pneumatic Controller

QS Pnumatic Control 1.jpg (28769 bytes) QS Pnumatic Control 2.jpg (14846 bytes)

This is the hand controller which allows the operator to override the interlock, charge, and fire the PDM machine. Safety is a primary concern with this machine so I've designed it with complete isolation for the operator. To accomplish this I use air pressure to control the functions eliminating any wires between the operator and the machine. 

 

Cart

QS_41.jpg (30500 bytes) QS_44.jpg (29811 bytes) QS_45.jpg (32180 bytes)

I'm attempting to build a cart that is half hand truck and half cart. If all goes well it will tip back on two wheels for moving between locations. It will also have a third front wheel to ease in positioning while in use.

 

QS Cart 46.jpg (30390 bytes) QS Cart 51.jpg (32095 bytes) QS Cart 55.jpg (27934 bytes) QS Cart 54.jpg (30490 bytes)

All the major components are mounted. I now need to disassemble it, paint the mounting board, then re-assemble.

 

Containment

containment 1.jpg (34167 bytes) containment 2.jpg (29106 bytes)

The containment box is made of 1/4" steel diamond-plate. The lid has overlapping seams to prevent fragments from slipping between the mating surfaces. The first shot shows the inside with the lid removed. The second shot shows the unit with the lid installed. I still need to add the catches, HV insulator and binding posts.

 

Containment 11.jpg (31018 bytes) Containment 14.jpg (31223 bytes) Containment 12.jpg (32956 bytes) Containment 16.jpg (34250 bytes)

Some better pictures of the containment and how the lid operates.

 

Completed PDM

Containment 17.jpg (24934 bytes) QS Complete Front 1.jpg (38763 bytes) QS Complete Rear 1.jpg (36086 bytes)

The first picture shows it nearing completion. The second and third pictures show the completed unit (minus some lexan shielding around the top HV wiring). The black cable on the left is four air hoses in a corrugated sheathing. These hoses carry supply air and control signals to/from the hand-held pneumatic controller.

The Accident

 

 

Questions and comments                Copyright 1997,2006 Brian D. Basura                This site was last updated 04/02/06