Jacob’s Ladder Climbing Arc Display


Commonly seen in older science fiction movies such as Frankenstein, thedramatic looking high voltage arc of the Jacob’s Ladder travels upward between two wires. The arc, which is a plasma of hot ionized gas, grows longer as it climbs up the wires.

For the operation of Jacob’s Ladder, a transformer generated arc of ionized plasma strikes at the small gap at the bottom of the rods, which is the point of lowest breakdown voltage. The heated plasma arc climbs up the diverging rods. Even when the arc reaches a width on one inch or greater, it still provides an easier path for the current to follow than the surrounding air. It works on the principle that the ionized air in the arc is at a lower resistance than the air around it and also the principle that hot air rises. Warm air pushes the arc up the ladder. The arc’s climb is also affected by the expected ‘high leakage’ or reactance curve of the transformer. For as long as Paschen’s Law will allow, the transformer arcs electricity across the bottom of the two wires. Paschen's Law states that the breakdown voltage is constant as long as the product of gas density and gap length is constant. Once the arc is established, the current in the arc will increase to the transformers preset limit. The arcs heat causes increasing resistance. We might expect that the transformer would try to decrease the voltage as the current increases. However, just above the arc there is a path that the transformer can easily maintain and which will lower its current. The arc climbs until the gap between the rods becomes too great. At the pinnacle of the two-rod course, the arc has reached the upper limits of the transformer’s power. Arc current is very low at the crest of the rods, and so the arc extinguishes only to re-ignite at the base of the two rods.

Despite the ease of acquiring the two major parts of the Jacobs Ladder, caution should be exercised if you decide to build your own Jacob’s Ladder.

The construction of a Jacob’s Ladder is not terribly complex. The climbing arc display only requires a high voltage power source (such as a DC-AC inverter using a television set flyback transformer) and a pair of metal rods arranged in a V configuration on an insulated and fireproof stand. Despite the ease of acquiring the two major parts of the Jacobs Ladder, caution should be exercised if you decide to build your own Jacob’s Ladder. The first concern is the dangers associated with high voltage applications. Another issue is that a Jacob’s Ladder (and Tesla Coils, also) are broadband RF sources when operating. The Jacob’s Ladder could potentially cause interference to radio, TV, cellular phone, cordless phone, and other communications equipment. There are unconfirmed rumors of the FCC tracking down and issuing fines to people who cause such interference. So it goes without saying, that you should proceed with caution if you construct your own Jacob’s Ladder.

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