Jacob's Ladder

"Build this exciting Jacob's Ladder and watch electric arcs ascend the ladder and evaporate in space. It works from a clever 12,000-volt power supply. Author Robert Iannini."

Jacobs Ladder, HV, Tesla, Wimshurst, Voltage Doublers, Kirlian, Lightning Bulb, Van de Graaff
 Re-written by Tony van Roon (VA3AVR)

People have long been fascinated by electric arcs--and perhaps put off by them. They show up as lightning, Tesla coil discharges, and long sparks that sting as you reach for the doorknob on a cold, dry, winter day. This Jacob's Ladder project turns electric arcs into a dramatic but harmless conversation piece.
If you build this project, you'll lean how a simple power supply operating from the 120-volt AC line can produce 12,000 volts. In addition to powering the Jacob's Ladder, the supply can power plasma displays, and it has even powered a light-duty, bench-type spot welder.
Perhaps you would like to know the origin of the term Jacob's Ladder. The Bible tells the story of Jacob's dream about a ladder that extended from earth to heaven. Jacob, the son of Isaac, was the father of the founders of the twelve tribes of Israel. Among sailors, however, a Jacob's Ladder is a long rope ladder that is hung over the side of a ship so the harbor pilot can climb aboard.

Climbing Arcs:
The power supply for this project forms electric arcs across two diverging stainless steel strips mounted in a protected case. The 16-inch long strips are mounted on insulating Teflon blocks to eliminate possible leakage. The stainless steel strips are angled with respect to each other so that the arcs form at the edges of the strips that are separated by about 3/16 inch at their bases but the strips diverge to a distance of about 2 inches at their upper ends.
The strips form a gap in the secondary winding of the output transformer. After power is turned on, the air dielectric breaks down due to the "almost" short-circuit state across the lower end of the gap, and an electric arc is formed.
As the arc heats up, thermal convection causes the arc to rise up the vee-shaped "ladder". As the plasma arc ascends the ladder, its length in creases, thereby increasing the arc's dynamic resistance and thus increasing power consumption and heat. This causes the arc to stretch as it rises and extinguish when it reaches the top of the ladder. When the arc extinguishes, the transformer output momentarily exists in an open circuit state until the breakdown of the air dielectric produces another arc at the base of the ladder and the sequence repeats.
The power supply for the Jacob's Ladder contains circuitry to protect persons and property from electrical shock or fire hazard if the ladder strips should be shorted accidentally when the ladder is operating.

Jacob's Ladder Schematic Diagram

Parts List:
All resistors are 1/4W, 10%, unless otherwise indicated.
           R1 = 0.47 ohm, 2 watt
           R2 = 82 ohm, 2 watt
           R3 = 2K, PC mount trimmer
R4,R8,R10,R12 = 1K
           R5 = 10K, PC mount trimmer
           R6 = 10 ohms, 1/4 watt
        R7,R9 = 27 ohms
          R11 = 220 ohms

 C1,C2 = 0.01uF, 1000V, ceramic
    C3 = 390uF, 200V, electrolytic
    C4 = 2.2uF, 250V, metalized polyester
    C5 = 1000uF, 25V, electrolytic
    C6 = 0.003uF, 50V, polyester film
    C7 = 0.01uF, 50V, ceramic
    C8 = 1.5uF, 100V, metalized polyester
C9,C10 = 1.2uF, 400V, metalized polyester

  BR1 = bridge rectifier, 4A, SIP
D1,D2 = 1N4007, 1000V, 1A, diode
   D3 = 1N914, silicon signal diode 
D4-D7 = 1N4735, 6.2V, 1W
 SCR1 = 0.8A, 200V, sensitive gate, TO-92, Teccor EC103B1 or equivalent
   Q1 = 2N2222, NPN transistor
   Q2 = 2N2907, PNP transistor
Q3,Q4 = IRF640, N-channel power MOSFET, 200V, 10A, Intern'l Rectifier or equiv.
  IC1 = 555 timer/oscillator
T1 = Driver transformer, 30 turns primary, 60 turns secondary (see text)
T2 = Output transformer, half bridge, 32 turns pri., 2500 turns sec. (see text)

Other Components:
S1 = Switch , SPST, panel mount, 10A, pull chain
F1 = Fuse, 3A, slow-blow

PCB or perforated board (see text); U-chassis (see text); mirror; metallized 
plastic (see text); transparent plastic covers (see text; L-Panel (see text);
stainless steel strips, 0.060-inch thick; 18-1/2 inches (see text) insulating 
blocks (see text); 2-feet high-voltage wire, 15 kilo-volt rating; 3-wire power 
cord with line plug; fuse holder; phenolic transformer insulator (see text); 
hookup wire; miscellaneous nuts, screws; rubber feet (4); linecord grommet; 
silicone grease; TO-220 mica washers; solder.

The following parts and kits are available from Innovation Unlimited, Box 716, 
Amherst, N.H. 03031; Telephone 603-673-4730 or FAX 603-672-5405:
  • Kit of electronic components and circuit board, less transformers--$69.50
  • Assembled and tested electronic circuit board--$89.50
  • Assembled and tested driver transformer T1--$9.50
  • Cores and bobbins for driver transformer T1--$4.50
  • Assembled and tested high-voltage transformer T2--$24.50
  • Cores, bobbins, and potting cap for high-voltage transformer--$14.50
  • High-voltage wire (15KV)--$0.50/foot
  • Teflon insulating blocks (2 required)--$5.00 (Tony's comment: Prices for the above are copied the way they were published in "Electronics Now" and may not be accurate anymore since dated from 1995. Also, although Innovation Unlimited still exists, there is no guarantee they are still selling the kits.)
  • Jacobs Ladder, HV, Tesla, Wimshurst, Voltage Doublers, Kirlian, Lightning Bulb, Van de Graaff 12,000 Volt Supply:
    The operation of the Jacob's Ladder depends on the current limited power supply that delivers 12,000 volts at 40 milliamperes from the 120 volt AC line. Refer to the schematic diagram of Fig. 1. The full-wave bridge BR1 rectifies the 120 volt AC line input, and resistor R1 limits the DC charging current of capacitor C3 to a safe value. The Jacob's Ladder project is powered by 150 to 160 volts DC derived from the 120 volt AC line.
    The drive circuit power is obtained by dropping the 120 volt AC line through capacitor C4 and current limiting resistor R2. Diodes D1 and D2 alternately conduct only in the positive direction, and their DC output pulses are integrated by filter capacitor C5. Zener diodes D4 and D5 regulate these DC pulses to peak values of 15 volts DC.
    Capacitor C4 and resistor R2 present a complex impedance so that most of the AC line voltage is dropped across the reactance. This configuration eliminated the waste of real power and heat losses that would have occurred by dropping the line voltage with only a resistor.
    The 555 timer IC1 is configured as a square-wave oscillator. The output frequency of its square waves is determined by the setting of the trimmer potentiometer R5 and capacitor C6. The frequency is is about 25 kHz for the values of R5 and C6 shown in Fig. 1. Resistor R12 limits the high-frequency setting to an acceptable value. Potentiometer R5 can be used to adjust the circuit's power output. Increasing the frequency reduces the circuit's output by increasing the inductive reactance of the transformer leakage inductance.
    The output of IC1 on output pin 3 appears at the bases of the current "source", NPN transistor Q1 and "sink" PNP transistor Q2. The emitters of this transistor pair are AC-coupled through capacitor C8 and resistor R6 to drive the primary of driver-isolation transformer T1. This drive prevents DC from flowing thought the primary. Resistor R6 dampens any overshoot that results from transformer T1's leakage inductance.
    The scheme provides a satisfactory source for driving the high gate-to-source capacitance of the two NPN switching power MOSFETs, Q3 and Q4. Transformer T1 is wound on a high permeability core with as few turns as possible to eliminate leakage inductance.
    The gate circuits of MOSFETs Q3 and Q4 contain 27-ohm resistors (R7 and R9) to slow their switching times. This eliminates possible parasitic oscillations that could occur if the MOSFETs were switched at their speed limit.
    Output transformer T2 has a half-bridge configuration so that MOSFETs Q3 and Q4 are only subjected to half of the rectified DC line voltage, or about 80 volts. Assuming that the voltage midway between capacitors C9 and C10 is about half of 160 volts (or about 80 volts), when Q3 turns on, the charge on C9 causes current to flow through T2 in one direction.
    When Q3 turns off, Q4 turns on, dumping the charge on C10 through T2 in the opposite direction. This drives the magnetic flux of T2 evenly and symmetrically, making full use of T2's core capability. The primary of output transformer T2 contains 32 turns, but its secondary contains 2500 turns. The ratio of these turns is approximately 1 to 78. When multiplied by the rectified line voltage of 160 volts DC, an output of about 12,000 volts peak volts is obtained across the secondary.
    This 12,000 volt output is the peak open-circuit voltage of the system, and it produces a short-circuit current of approximately 40 milliamperes. This current is limited by the leakage inductance caused by the loose magnetic coupling between the primary and secondary circuits of transformer T2. This leakage inductance can be controlled to some extent by placing air gaps between the cores, changing the reluctance of the magnetic circuit.

    Safety Provisions:
    Because this project is operated from the 120 volt AC line, fault and safety shutdown provisions are included. They are provided by silicon controlled rectifier SCR1 connected as shown in Fig. 1 with its anode in series with diode D3. When the gate current reaches a specified threshold, the SCR is triggered on and latched by holding current through resistor R4. Trigger pin 2 and Threshold pin 6 of IC1 are now clamped to ground, thus preventing oscillation and turning off the circuit.
    The signal current for the gate of SCR1 is obtained from the capacitive connection to the actual core of the output transformer T2. This connection is made by winding three to four turns of insulated hookup wire around the core of transformer T2. In effect, it is a capacitive wire pick-up probe. As long as output power is flowing between the output connections of T2, the Jacob's Ladder will continue to operate.
    If, for some reason, one of the output leads (vee strips) is grounded, a return current is forced to flow by capacitive action between the core of transformer T2 through the wrapped-wire pick-up probe. This current then turns on SCR1, shutting down the Jacob's Ladder.

    Building the Circuit:
    The high-voltage power supply circuitry for the Jacob's Ladder can be built by point-to-point wiring methods on a 5-1/2X2-1/4 inch piece of standard perforated circuit boards (holes spaced 0.10 inch on centers) or on a circuit board available from the source given in the Parts List. Drill mounting holes in the four corners of the circuit board before inserting any electronic components.

    parts lay-out

    All of the electronic components with the exception of transformers T1 and T2 are standard, off-the-shelf components available from electronics stores and mail-order distributors. However, the transformers must be custom wound. Both transformers, completely wound and tested, are available from the source given in the Parts List. Alternatively, you can wind your own transformers if you have some experience in doing this. Some useful information on winding these transformers and material selection is given later in this article under the heading, "Winding the Transformers."
    Refer to the schematic in Fig. 1 and parts layout diagram Fig. 2. The parts layout diagram gives the approximate locations of all components except for switch S1 and transformer T2, which are off-board components. There is nothing critical about parts placement, and suggest layout of Fig. 2 is based on keeping interconnecting wiring as short as practical. Be sure to make the gate connection go MOSFETs Q3 and Q4 as short and direct as possible.
    Begin by inserting and soldering all components except MOSFETs Q3 and Q4. Observe the correct polarities for all silicon diodes (D1 to D3), Zener diodes (D4 and D5), and electrolytic capacitors (C3 and C5. If you wire point-to-point, do not trim the leads of the components until you have made use of as many excess leads lengths as is practical to form interconnections between components.
    Then insert the TO-220 packaged MOSFETs Q3 and Q4 close to the outer edges of the circuit board in the locations shown in Fig. 2, with their metal tabs are facing outward. In a later step, the tabs of Q3 and Q4 will be fastened to the sides of a U-shaped channel that functions both as a heat sink and as a support for the circuit board.
    Carefully examen all the electronic components on the board to be sure that they are correctly placed and oriented. Examen all solder joints to verify that there are no inadvertent solder bridges or cold solder joints (a joint soldered too fast and does not adhere properly). Make any corrections at this time before proceeding. Then set the completed circuit board aside.

    Assembly diagram

    Product Enclosure:
    Figure 3 illustrates the author's enclosure for the Jacob's Ladder project. It was designed to meet two objectives: 1. to meet all reasonable safety requirements by providing adequate insulation between people and flammable materials and the enclosed high-voltage circuitry, while at the same time protecting the circuitry form dust and dirt. 2. to be simple enough to be made by persons with minimal carpentry skills form materials readily available at hardware and home-improvement stores.
    Many variations on the author's enclosure design are possible including changes in exterior and interior dimensions and the substitution of more expensive wood for the framing. However, it is imperative that all provisions for ventilating both the circuitry and the vee "ladder" to dissipate any heat buildup be followed, but make sure that those spaces are not large enough to admit fingers or the small hands of curious children.
    The overall case dimensions are 24 x 12.5 x 4 inches. The closed H-shaped frame was made from 3/4-inch thick x 4-inch wide soft wood. Slots that are 1/8-inch wide and 1/4 deep were milled 1/8-inch in from each edge of the inside surfaces of the frame members to accommodate protective transparent plastic covers on the front side and a metalized plastic mirror on the back side. (These protective sheets could be fastened directly to the case edges with screws.)
    The bottom of the case and the back of the lower circuit/transformer compartment is covered by an L-shaped aluminum plate that serves as the vertical support for the circuit board and output transformer. Holes drilled in the bottom of this plate permit circuit ventilation and access to the on-board trimmer potentiometer R3 and R5. Another hole id formed in the back of the plate for mounting on-off pull switch S1.
    Figure 4 provides general information on the sizes and shapes of the principal wood and aluminum parts. Notice the holes drilled in the top member of the frame for cooling the ladder compartment. The author's prototype frame was made by assembling the wooden frame with screws after the clear 1/8-inch plastic front windows and rear mirror were cut to fit the milled slots.
    The transparent plastic cover for the ladder compartment was cut 1-inch shorter than the inside dimensions of the frame to provide a bottom opening for ventilation. This ventilation slot is important and should be there regardless of any dimensional changes you might want to make in the frame. The cover for the circuit compartment protects that compartment completely. It is transparent plastic in the prototype so that the circuitry could be seen, but it could be opaque.

    Jacob's Ladder Enclosure

    Project Metalwork:
    No hole sizes or location dimensions are given here for the enclosure components. Those are left to the builder's judgment. Cut and form the U-shaped aluminum channel from No. 22 gauge sheet aluminum, as shown in Figure 4. Drill hole in both ends of the channel along the centerline. Then, using the drilled holes in the circuit board as a guide, center-punch and drill four holes for mounting the circuit board to the channel. (These can be omitted if you elect to bond the circuit board to the channel with hot plastic glue drops.)
    Cut the L-shaped panel as shown in Figure 4 from No 22 gauge sheet aluminum. Before bending the front lip of folding the plate, drill 1-inch diameter holes for circuit cooling and access to trimmer potentiometers R3 and R5. Above the fold line, drill another hole for the linecord (powercord), large enough to admit a rubber or plastic grommet, and drill a hole to accommodate chain-pull switch S1. Then bend the flat plate 90° along the fold line and bend up the front lip.
    Drill two holes evenly spaced within 2 inches of the ends of the stainless steel "ladder" strips, and bend those 2-inch long sections approximately 90° with respect to the rest of the strips. Note: Stainless steel was selected for the ladder strips because the electric arcs will not cause the strips to oxidize or corrode, and tests showed that stainless steel permits easier starting of the arcs than other metals.

    Insulator Blocks:
    The two metal strips that form the "ladder" must be mounted on insulators that have high dielectric strength. The insulators in the prototype were made from Teflon blocks that measure 1-1/4x1x3/4 inch high. This material can be drilled and tapped, and it is strong enough to withstand the heat created by electric arcs. Individual Teflon blocks are available from the source in the Parts List.

    Project Assembly:
    Jacob's Ladder, T1 With the completed circuit board inserted in the channel, elevated slightly above the bottom of the channel, mark, centerpunch and drill the holes in each side wall for fastening the tabs of MOSFETs Q3 and Q4. Be sure to deburr and perhaps countersink slightly the holes in the channel so that the tabs on the MOSFETs will be clamped securely against the channel walls. Cut and trim the ends of two 3-inch lengths of insulated, stranded linecord to the circuit board, as shown in Fig. 2, to make the connections with the linecord. Insert and solder the ends of the wires on on-off switch S1.
    Attach the circuit board to the U-channel with screws and nuts, using several nuts as standoffs to isolate the circuit board from the channel. Align the tabs of MOSFETs Q3 and Q4 with the holes in the sidewalls of the channel, insert insulating mica washers with a film of silicone grease between each tab and the channel walls, and fasten them with screws and nuts.
    Cut a 2-1/2 inch square of phenolic laminate or circuit board stock between the base of transformer T2 and the bottom of the channel. Bond the transformer to the insulator and channel base with epoxy or hot glue.
    Drill two holes through the wooden frame member between the two compartments, and insulating blocks. Drill a singe hole in the opposite sides of each block and fasten the ladder as shown in Fig. 3.
    Then attach the insulation blocks and strips to the frame member with screws. Fasten the bent metal strips so that they are offset by about 30°, as shown in Fig. 3. The base strips are diagonal across the insulator blocks so that the corner edges are separated by about 3/16 inch. The upper ends of the strips should be about 2 inches apart.
    Fasten the channel with transformer T2 and the circuit board to the L-shaped panel with screws and nuts, as shown in Fig. 3. Complete the installation of switch S1 and the linecord with a grommet, and complete all soldering. Be sure the L-shaped metal panel is hard-wire connected to the earth ground by means of the green wire within the three-wire power-cord. Assemble the enclosure with its plastic covers and aluminum base plate. The Jacob's Ladder is now complete.

    Adjusting the Ladder:
    Carefully examine your work to be sure that there are no inadvertent short circuits of cold solder joints. The circuit is now ready for testing. First, adjust potentiometer R5 as follows:
    1. Disconnect one end of R1 to Q3.
    2. Connect an oscilloscope to the Q4 gate.
    3. Plug in power cord and turn on power.
    4. Adjust R5 for a period of 40nS so 15-volt squarewaves are symmetrical.
    5. Shut off power, reconnect R1, and connect the oscilloscope to the Q4 drain.  
       Turn on power.  A near perfect squarewave should appear, and it should remain 
       constant as arcs form and reform. 
    Adjusting procedure for the ground-fault potentiometer R3 to shut off the circuit if there is ground-fault current:
    1. Turn off power and set wiper of R3 for maximum sensitivity.
    2. Disconnect a high-voltage lead from a ladder strip, and connect it to ten 
       1-watt, 100 kilo-ohm resistors in series.  (This simulates a 10-milliampere 
       ground current.)
    3. Apply power and verify that the circuit shuts down.  Turn off power, adjust R3 
       slightly clockwise.  Reapply power until high voltage stays on.  Note: allow 
       time for C3 to discharge before re-applying power or SCR1 will stay on.
    Jacobs Ladder, HV, Tesla, Wimshurst, Voltage Doublers, Kirlian, Lightning Bulb, Van de Graaff Winding the Transformers:
    Figure 5 is a "footprint" diagram of drive transformer T1 with callouts that can be related to those found on the schematic Fig. 1. The cores and bobbins for this transformer are from Philips (Ferroxcube) Components, Saugerties, NY). The cores are No. E187 made from 3E2A molded ferrite material. The plastic molded bobbins are Part No. E187PCB1-8. These parts are available from the source given in the Parts List.
    Transformer T1: Wind the first 30 turns trifilar (three wires in parallel) from No. 30 AWG magnet wire and the remaining 30 turns as single wire turns. Solder the ends of the windings to the pins, insert the E-core, and tape the assembly together securely.
    Transformer T2: The core of transformer is No. 4162S from Samhwa USA, Chatsworth CA, with matching seven segment bobbin, cup and primary bobbin. These parts are also available from the source given in the Parts List.
    Start winding the secondary bobbin by securing the magnet wire to a pin insulated on the bobbin end and wind between 300 and 400 turns of No. 37 AWG magnet wire on each of seven segments. Snap the cup in place and solder the output leads. Fill the cup with epoxy or RTV Silicone when you are satisfied that the transformer has been wound correctly.
    Wind eight turns of No. 30 twisted wires on the primary bobbin and tape the windings in place. Form the air gap of the primary section with 0.005-inch thick Mylar tape and form the air gap for the secondary section with 0.010-inch thick Mylar tape. Tape of clamp the two sections together with a heavy rubber band.

    Parts List:
    All resistors are 1/4-watt, 10%, unless otherwise noted
       R1 = 0.47 ohms, 2 Watt
       R2 = 82 ohms, 2 Watt
       R3 = 2K, trimmer potentiometer
    R4,R8,R10,R12 = 1K
       R5 = 10K
       R6 = 10 ohms
    R7,R9 = 27 ohms
      R11 = 220 ohms
        C1 = 0.022uF, 50WVDC metalized film
    C3-C12 = 0.001uF, 2000WVDC ceramic disk
       C13 = 220uF, 25V, electrolytic
       C14 = 4700uF, 35WVDC, electrolytic 
    Note: There is no C2.
    D1-D10 = 1N4007, 1A, 1000PIV, silicon rectifiers connected in series (see text)
       D11 = 1N4007, 1A, 1000PIV, silicon rectifier 
        Q1 = TIP31A, Darlington transistor
        U1 = MC1458BAL hex, inverting Schmitt trigger, IC
       BR1 = 6A, 50PIV, full wave bridge rectifier
      Led1 = Jumbo green light emitting diode
    Other Components:
    Ne1 = Ne2 neon lamp
     T1 = Ferrite core step-up transformer (see text)
     T2 = 12 Volt, 2A, power transformer
    PL1 = 117 volt AC plug with line cord
    Perfboard materials, enclosure, battery, heat sink, IC sockets, battery, wire,
    Battery, Battery holder, solder, hardware, etc.
    Please Note: don't ask for additional information. This is all there is. Don't email me or leave messages in regards to this project in the "Message Forum"; they will be deleted without prior notification. NO I don't sell a kit, NO I don't have a pcb either. The 'suggested' parts lay-out diagram refers to perforated board. Meaning, you do point-to-point wiring and soldering.
    However, on the positive side, I may try to put a kit together with all parts and maybe a pcb if there is enough interest.

    Copyright and credits:
    This article originally appeared in "Electronics Now" magazine, December 1995. It was written by the author Robert Iannini. Published by Gernsback Publishing. (Gernsback Publishing is no longer in business).

    Electronics Now cover, Dec 1995


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    Last Updated July 24, 2010