DIYbanter - View Single Post - Transformer shot! (was scope SMPS/ capacitor venting)

MJC

In article , says...

It looks like the thing may have drifted a little bit out of resonance
over the years. That can happen, electronic parts age and tolerances
slowly increase. Running out-of-resonance, the power factor of the
resonant circuit was probably no longer close to one, but instead the
resonant circuit began to pull reactive power. If you try to drive an LC
circuit with a frequency that is slightly wrong, the driving source will
still force the LC into its frequency, but there will be a phase shift
between voltage and current. The further off the frequency, the larger
the phase shift will become. A phase shift means that a load is no
longer purely resistive, but also reactive (either capacitive or
inductive depending on direction) and so the power factor gets lower. As
the power factor gets lower, the total current draw increases (imagine a
constant current due to resistive load plus an additional current due to
the reactive part of the load, which increases).

Your wonderful description of resonant circuits reminds me of an
experience I had as an apprentice. I was given the job of trying to lay
down a silicone insulating film generated by polymerising a silicone
vapour in a high voltage AC plasma. (I don't remember why it had to be
AC.)

We didn't have any special HV AC supplies but stores did have a signal
generator and powerful audio amplifier. I managed to scrounge a large
open-centred coil (meant to generate a magnetic field around a bell-jar)
and a collection of high voltage capacitors, waxed paper in steel cans
with ceramic terminals on top.

With these I built a series LC circuit which generated a satisfactory
plasma. I'm afraid I don't recollect any measurements. Health-and-safety
consisted of large hand-written warning notices!

However despite being distracted by my plasma I also noticed that the
poor capacitors, excellent with DC no doubt, didn't like the AC current
they were subjected to, and bulged, leaked and fizzed. The experiment
was terminated abruptly!

Mike.