
Resonant MOTs
Resonant
MOTs
While a single MOT doesn't give very impressive arcs, two MOTs and a
four MOCs will give incredible arcs. (MOT = microwave oven transformer,
MOC = microwave oven capacitor) Running MOTs in resonance has to be the
easiest way to get massive arcs as only 7 components are required, all
of which can be found in microwave ovens. This also makes then
exceptionally dangerous because no skill or knowledge is required to
construct a resonant stack.
How can it give bigger arcs than a two MOT system? Series resonance.
MOTs are designed to have a large leakage inductance, which is the
inductance a winding will have when a different winding on the
same core is
shorted. It can be thought of as an external inductor in series with a
winding on the core. So when putting a heavy load on the transformer
(like an arc)
instead of the winding inductance dropping to zero it will drop to the
leakage inductance value which is more than zero. This extra inductance
can be used to form a resonant circuit, by
including some extra capacitance. MOCs are conveniently sized and rated
perfectly for the task. The resonant circuit
consisting of the MOT's leakage inductance and capacitors allows much
larger currents to be drawn, and thus longer arcs. To keep the arcs
stable a ballast is used. I've found that a primaryshorted MOT put on
the secondary side works good. It didn't function as well on the
primary side, so maybe it contributes some inductance to the resonance
circuit making it more in tune with mains. Either way the arcs couldn't
be drawn out very long without it. Although 1 MOC could probably be
used alone it's best to give them a
good margin. (A trained eye will see that the 4 MOCs have the same
capacitance as one.) The resonant voltage rise will put much more than
the 2kVAC across them that they're rated for. Mind the phasings, if out
of phase the arcs can't be drawn
out and will just be short puffs. See Jan
Martis' page for more info.
Youtube video of arcs!
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