This project was conceived out of boredom and had one simple goal, draw some High Voltage arcs. Oh and it had to be cheap. The Jacobs ladder is a classic device designed to initiate an arc and make it rise between two separating pieces of metal. Typical Jacobs Ladders are high voltage but low current devices producing thin arcs. Using some parts found in microwave ovens we can create a high voltage resonant circuit and draw some nice fat arcs.
SAFETY NOTE: This circuit generates voltages which can instantly kill without warning. There is no current limiting, earth fault protection or anything else which will help your chances of survival. Don’t replicate unless you know exactly what you are doing.
The following parts were scavenged to make this Jacob’s Ladder
- 4x microwave ovens (high voltage transformers, and capacitors)
- Two long band elements of a TV antenna
- An extension cord (cut to provide us with a Live and Neutral cable).
- A piece of bamboo from the garden as a safety pole.
- A screw to initiate a short.
All together it is hooked up as follows:
Theory of Operation
The magic behind this Jacob’s ladder relies on the theory of resonance. When a tuned inductor and capacitor are connected in series or parallel the generate a resonance at a specific frequency like a tuning fork. As any AC signal approaches this resonant frequency it experiences sudden gain. This is used in electronics to boost weak signals and tune other undesirable signals such as in a radio tuner. Resonance is also what drives the power in a microwave’s magnatron. In our circuit resonance provides a high current boost allowing our arcs to sustain for longer and get drawn wider without extinguishing.
The series / parallel combination of capacitors shown is required as doubling the voltage rating by connecting capacitors in series halves their capacitance, so we need to connect another pair of capacitors in parallel to get us back to our original capacitance. In addition to 4 capacitors and 2 microwave transformers connected in series, a third microwave transformer acts as a ballast. This is required as an arc acts as a short circuit and drawing arcs will quickly lead to tripping a fuse without some form of current limiting. By shorting the primaries of a transformer and connecting the secondariness in series the transformer acts as an inductive ballast limiting the current draw and preventing any trips… oh and it gets very hot in the process. This same principle is used in iron core ballasts for florescent lights.
A non-conductive stick has a screw through the end which is electrically connected to one side of the Jacob’s Ladder. This allows us to kick start the circuit by generating a brief short circuit all the while not killing ourselves in the process.
Well the results speak for themselves. Beautiful arcs are drawn from and sustained for several seconds. Of note is the fact that the arc has a different colour depending on which material it jumps from. From the aluminium ladder the arc draws blue, from the steel screw the arc draws orange. When the cable briefly came in contact with the arc the arc jumped to a section of copper and turned green.
The arcs will rise up the ladder and extinguish themselves as the distance between the top points of the ladder combined with the updraft of air being heated to 70,000 degK cause the arcs to become too long to sustain themselves.
Maybe I need to up the voltage…