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Sync RSG and hot resistors
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From: Gary Lau 09-Feb-1998 1136 [SMTP:lau-at-hdecad.ENET.dec-dot-com]
Sent: Monday, February 09, 1998 10:46 AM
To: tesla-at-pupman-dot-com
Subject: Sync RSG and hot resistors
>> What really surprises and disturbs me is how hot my choke series resistors
>> now run. With my static-only gaps, I was using a pair of 750 Ohm/50W
>> units. These used to run somewhat hot, but smoked in a very short time
>> with my sync RSG. I've gone to 500 Ohm/75W units, but even these begin
>> to smell like they're burning after about 15 seconds. Assuming they're
>> dissipating 100W each, that means they're passing 447 mA??!!
>
>> Observing the RSG, the gap arcs appear to be about .5" long, does that
>> sound right? (This is the length of the arc before it breaks, not the
>> RSG gap spacing, which is about .03")
>Gary,
>
>Are you sure the gap arc is being pulled out .5", or is this just the
>*fireball* of hot plasma that splashes out from the gap when it fires?
>If the arc is being stretched by .5" this is strange. Are the electrodes
>more than 1/4" wide? I figure maybe the gaps are refiring if they're too
>wide. Refiring gaps will cause a heavy current draw and heat the chokes,
>and hurt the performance. Yet, with the RQ gap in series, this should
>stop re-firing from occuring, so it's a mystery to me. Besides neon
>trannies probably don't provide enough current to cause re-firing in
>general. Maybe a quench problem of some sort, power arcing?
>Although there shouldn't be. Do the spinning
>electrodes get hot? Maybe the chokes are resonant and heating up?
>
>I'm not sure I remember the size of cap in your system, is it .011uF to
>.014uF or so? If it's a smaller cap, it may have been firing twice per
>half cycle using the static gaps, but firing once (of course) using the
>sync gap, which would hurt the performance. I forget also what size
>toroid you're using, are you obtaining a different amount of streamers
>now from the toroid? It's an interesting problem. Forgive me if I've
>already discussed some of these issues previously.
>
>John Freau
My RSG has a 9" dia .09" thk G10 disk (horizontal) with four brass 1.5"
8-32 screws sticking vertically out of one side. There is 2" wide copper
foil on the perimeter of both sides of the disk connecting the four
screws. The two stationary electrodes are .06" thk x .625" wide copper,
90 degrees apart, also vertical, positioned such that each gap is about
30 mils x .625" wide (parallel to screws) at presentation. The dwell
time in this configuration should be very brief. The rotating screw
electrodes get plenty of cooling by virtue of their rotation, and the
stationary electrodes are massively heatsinked. My cap is .01 uF.
Since going to the sync RSG, it's clear my cap is charging to a much
higher voltage, evidenced by arcing between my outermost primary turn to
strike rail. I've since removed the outermost turn.
I made a new discovery last night. The secondary tap that was correct
for my static gap system is no longer right, I've had to move out 1-2
turns. My theory is that the higher voltage bangs are creating a denser
ion cloud about my toroid, lowering the secondary Fres.
My top load is two toroids - a 4.5" x 15.5" plus a 6" x 22" unit. With
the static gaps only, a nail on the 6" x 22" unit would produce a
singular breakout from that point. Now with the sync RSG, I get a
breakout from the nail, plus from several other places as well. This also
suggests a much higher cap voltage per bang. The surface of the 6" x 22"
unit is just the corrugated aluminum dryer duct. My next task is to smooth
it out. I'm wondering if it needs to be bigger still?
With the corrected tuning, I'm now seeing 40" discharges, still not the
43" performance I had with the static gaps. In addition to being
somewhat shorter, they are less bright, but much LOUDER. I'm wondering
if I add another four rotating electrodes for 240 pps, how that would
affect things. Has anyone else tried a sync 240 pps system?
Still no progress or clues on why my R's are toasting, unless my NST and
cap are so powerfully resonant that it can pull >400 ma from that puny
60 ma secondary.
Gary Lau
Waltham, MA USA