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12" secondary observations
Original poster: "Gregory Peters by way of Terry Fritz <twftesla-at-qwest-dot-net>" <s371034-at-student.uq.edu.au>
I quickly fixed my burnt out 12" secondary by rewinding the bottom 3-
4" with PVC insulated stranded wire, held in place only by hot glue.
I got one decent photo of a 9 foot strike. Go to:
and look at the last two pictures.
I made some observations, see some more info on my page.
1. Even at 400BPS (sync), 0.11uF is not enough capacitance for the
power I have available (about 12-13kW, with a bigger fuse). I need a
2.I feel the gap is not adequately quenching. Above 220v on the 270v
variac, performace drops of quickly. I don't think the gap can handle
the extra power. This will be even worse when I make a bigger cap. I
need to drop the frequency of the system to allow the use of more
primary turns to increase the surge impedence and reduce gap losses.
It is currently tapped at turn 7, despite a very low operating
frequency of 68kHz. I would like to use a bigger toroid, but the coil
can't break out of the one I've already got without a bleeder rod, so
I'm going to wind a "John Freau" secondary using 1300-1500 turns
(currently 900 or so).
3. I at last know why the last two secondaries failed.
a) Secondary was overcoupled. Raising it 2" solved this, and probably
the PVC coated wire at the base.
b)Probably as a result of overcoupling, I was getting secondary-
primary arcing (as always, on the side I can't see). Fortunately, I
was able to wipe away the carbon track, wrap some LDPE around the
base of the secondary and continue. This was only allowed due to
the "ruggedness" of the stranded PVC coated wire. The spacewinding
effect of the PVC insulation helped in this regard. My new secondary
will not have this, but I hopefully will prevent the arcing BEFORE it
4. Fres of bare secondary: ~125kHz, Fres of secondary with toroid:
~75kHz. I set the primary at 6% lower and the tuning was accurate to
within 1/3 of a turn. All measurements were made without the
secondary sitting in the primary.
5. Longest spark recorded was ~10 feet, with no adjustments being
made to toroid height, etc. Tuning was fairly good, but otherwise
coil was poorly set up. I can't wait to set it up properly and wind
up the power with more tank cap.
6. More info on my page given above.
The other, other Greg.