Raise the secondary....because! (fwd)
---------- Forwarded message ----------
Date: Sun, 12 Jul 1998 16:18:38 -0600
Subject: Raise the secondary....because!
I have 5 scope pictures at:
I set my coil at the point were the quenching sometimes works on the first
notch and sometimes it doesn't.
In all pictures, the top trace is the output voltage at 100kV/div. The
bottom trace is the secondary current at 2.5 amps/div.
This shows my coil with good first notch quenching. Note that you
can see the zero current crossing bursts from the gap in the bottom current
waveform. The gap is quenching at about 23uS and there are 5 current
crossing bursts. Note that the current bursts are 90 degrees out of phase
with the secondary current as lumped parameter models predict. No standing
waves here! It is scary how good the models are getting!! Phase, timing,
delays, levels..... all dead on! See schem.jpg for the schematic.
Same as above with time scale stretched out.
This shows the coils performance when the quench fails. Note that
the output voltage is somewhat higher as modeling predicts. The gap is
firing 17 times instead of 5 as in the good quench case. Obviously wasting
It is interesting to note the current crossing spike is absent where
the first notch should occur. Also note the "painful" final burst of the
spark gap. These are typical of quench failure.
Same as above with expanded time scale.
This is the voltage waveform with about foot long streamers (250kV
peak). Note the linear decrement. It appears that the steamers are drawing
power from maybe 15 to 20 of the cycles. Obviously, having the quench fail
will starve the streamers of voltage far too soon. Judging from the
ringdown profile, The arc is loading the coil at about 6 mega-ohms (trust
me, I know these things :-)).
These pictures clearly illustrate why good quenching is important. If the
quench fails the following things happen:
1. The output voltage peaks fall off far too soon and cannot supply the
2. The gap is dissipating much more energy and is wasting much more power.
3. The gap, capacitors, neon, etc. have much more stress.
This clearly explains why, when quenching is good, the gap quiets
and cools down, the streamers improve, and life is good!