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2 meter arcs with 8 MOTs

    I've built another high current high voltage power supply with no other purpose than drawing giant arcs. This time up to 2m long. This high voltage power supply contains 8 MOTs (transformers from microwave ovens) connected to two groups of four. In each group, the MOTs are connected both primaries and secondaries in parallel. These two groups are then connected in series (both primary and secondary) and powered from 400V~ phase to phase mains voltage. When connecting the power supply to the mains, the inrush current has to be limited. For this I use a modified ballast for a 150W high pressure sodium discharge lamp (made by TESLA). I've removed the "U" part of the iron core, leaving only the "T" part. After the modification, its inductance is about 35 mH. This inrush inductor could be replaced by a heater element, probably rated 230V and at least 2kW. After connecting the power supply to the mains, the inrush inductor is bypassed using a switch. On the secondary side there are resonant capacitors taken from microwave ovens. Each capacitor is approximately 1uF 2100V~. I got the best results with 12 to 16 microwave oven capacitors (6 to 8 on each side). If I used even more capacitors, the circuit breaker would trip too early. The reason to use secondary resonant capacitors is simple: With them, you can get longer high voltage arcs :). Thanks to the resonance, you can reach a high secondary current while the primary current isn't too high for the circuit breaker. This power supply is not designed for continuous operation. Output voltage is about 4000V~. With 14 capacitors (7+7) and 400Vac input, this high voltage power supply draws about 4.3A idle current, about 23A with the output shorted out and up to 41A when drawing the longest arc. My 25A class B circuit breaker does not trip sooner than after tens of seconds of operation. The secondary arc current is about 7A. As one of the electrodes I used an upside down metal can with salt on top. The salt colors the arcs to brighter orange and probably makes them a bit longer.

    Warning! The output voltage of a microwave oven transformer (MOT) is around 2100V AC and current ranges in the order of Amperes. Using more MOTs brings even higher voltages and currents. Risk of serious electric shock, severe burns and death. The output high voltage is lethal and can bridge large distances. The shock may therefore occur without direct contact with live conductive parts. Capacitors can remain charged to a dangerous voltage even after disconnected from power. Arcs produce poisonous gases like ozone and nitrogen oxides. Arcs emit strong visible and ultraviolet radiation. Risk of eye and skin damage. Risk of fire. You do everything at your own risk. This is not an instruction. The author accepts no responsibility for any harm to your health, life, property or other.

High voltage power supply with 8 MOTs and 12-16 microwave oven capacitors, running on 400Vac phase to phase voltage.

Me drawing up to 2m long arcs.

Me drawing another giant arc from my 8 MOT high voltage power supply.

One end of the arc is now more orange-colored by the sodium in the salt than the other. I need to add more salt.

Another big arc.

And yet another long high voltage arc.

High voltage power supply with 8 MOTs and 16 microwave oven capacitors.

High voltage power supply with the inrush inductor added. 7+7 capacitors. One of the electrodes is an upside down can with salt on it.

Inductor to limit the inrush current and a switch to bypass it after the power supply is connected to mains.

Video - drawing up to 2 meter arcs :).

Added: 20. 4. 2020