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Power Arcing
All,
I was running my coil at somewhat higher power today (off three 15 KV 60
MA neons instead of two), when suddenly my vacuum gap motor stopped
running. After tearing it apart, I discovered that a field winding wire
had arced over to the 3rd-wire grounded motor frame, melting and
openning up the #22 AWG wire. From the looks of it, a high voltage arc
had initially bridged the gap, and was followed by a heavier flow of
120V power which blew open the wire. An easy repair was made via solder
and shrink tubing, and the unit put back into service. There's no EMI
filtering of any kind on the lines going to the motor, but this unit had
functioned just fine for 5 months.
The coil was again powered up, and the same thing happenned again! The
cord to the unit is the standard 3-wire one which came with the
Shop-Vac, and is about 6 feet long. It looks like high voltage is being
picked up or induced into the cord somehow. Before powering up (or
blowing up) a different motor, I need to determine the source and
correct it. My first guess is that its common-mode RF pickup from the
near-field radiation coming from the coil. I am planning a couple of
potential changes, such as running power through shielded power cords or
flexible conduit, and adding EMI filters.
I'm also concerned about the RF energy coupling into the aluminum
siding, window frames, and guttering, and plan to make sure that these
are adequately grounded to AC ground. It looks like any length of wire
or cable in the room with the coil will also pick up a goodly amount of
induced RF from the coil AND the sparks.
What are some of the techniques used by the more experienced coilers to
control these?? I'm concerned about boosting power (especially with a
pig) until I get this situation under control! Thanks in advance!
Safe coilin' to ya!
-- Bert --