RE: My PT is loud!

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "sundog by way of Terry Fritz <twftesla-at-uswest-dot-net>" <sundog-at-timeship-dot-net>

Drew,

 1/2" gap is pretty wide for a 10kv setup.  For pulling 10kv out of that
thing, all I can say is that you got a tough PT.  Not industructable, just
tough.

 Set the gap so that the pt can fire it every time it's turned on, *without*
the caps in the circuit.  That's the proper distance for the safety gap.
Set the main gap to about 1/2 to 2/3 of that distance.  The wider themain
gap is, the harder you're going to be on the caps.  Also, your saftey gap
should discharge through the primary, just like the main gap. If it's
directly across the cap, and fires once then power-arcs (like a pig system
when the SRSG fails), the RMS current on the caps is *not* limited and they
will get hot fast. This is important with high-powered systems, or where
your RMS current capabilities are limited (EMMC, rolled caps, etc).

 As for the tranny and cap buzzing but not firing, either the cap is too
large (loads the tranny down too much to reach firing voltage), or you've
got the gap opened too far up.  Usually when I hear a NST and/or cap groan
it's because it's a resonant cap, and the gap either is too wide or the SRSG
falls out of sync (it's breaker popped without me knowing.)  Either way,
it's a Bad Thing(tm), as the voltage skyrockets with a resonant circuit. The
only limiting factor is the gap setting, the capacitors' voltage handling
ability, and the insulation of the PT.  You probably don't want to destroy
the bags or the PT.

Given that your PT is running ~3x the normal voltage anyway, I'd *highly*
advise to run a pretty narrow gap, or you'll sacrifice the PT to the smoke
gods.  It's insulation is gettin' a lot af abuse already, a resonant
situation makes it worse.  Do you have a DMM or capacitance meter to measure
the capacitance of the cap?  Radio shack, sears, and most electronic stores
sell DMM's that can read capacitance.  I also recommend a clamp-on ammeter,
as you don't want to put a DMM inline with the PT while running TC service.
That and I don't trust the thin little leads supplied with the DMM to 10A or
1000v.

 What you might want to do is scrounge up some MW oven parts (namely the
caps and diodes), and put a voltage doubler on your PT.  That way you can
run it at 4200v, and double that to roughly 9kv, easily enough to run a TC.
You'll also be feeding the tank cap DC at that point, so a resonant
condition can't occur (only happens on AC.)  Your total output power will be
a bit less than it would be feeding the PT 300v, but I can almost guarantee
a longer life for the PT, and the lost performance (a few " of spark
probably) will be worth the PT not dying.  Also, the 8-9kv will be easier on
the caps (at 10kvAC the cap sees 14kvDC, at 9kvAC it sees 12kv).  Voltage
doublers are easy to build, and the parts are cheap, if not free at the
local dump (MW ovens).  Your PT will thank you.  Keep the MV trannies also,
they're useful for ballasting.

 Keep it safe!
												Shad


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Wednesday, February 21, 2001 10:06 AM
To: tesla-at-pupman-dot-com
Subject: My PT is loud!


Original poster: "Drew Murray by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<drewallmighty-at-hotmail-dot-com>

Hello,
I am almost finished my coil. I took everyones advice and redid my primary.
I don't want to risk cooking my secondary with the Vertical helix primary. I
have finished winding my 8" x 32" pvc secondary. I gave the pipe a thin coat
of poly before i started winding. I didn't have much left in the can as i
used it for my last coil. I have all of the current limiting and power
control equipment set up for the PT and i have been having fun watching the
heat waves totally distort the wall behind it from my jacobs ladder. It can
climb untill the flame is something like 5" long. Anyway,
I have been experimenting with around 323 1 gallon zip lock bags with the
zip locks cut off, and some foil plates, trying to make a capacitor. I
noticed that if i got the capacitance way too high, and i turned up the
variac to the pt, no sparks would jump the 1/2" saftey gap on the pt. It
worked with a 16 wine bottle salt water cap! When i turned it up to around
60% A really loud buzzing/humming noise would come from either the PT or the
capacitor, which i have watched vibrate voilently before. It would stay loud
until i turned everything off. What the heck is happening here? It is a
120:4200  -at- 1000va, but i have been feeding 300v into it from a step up
transformer, so i can get 10500v out of it. 4200 just wasn't enough. and
could somebody show me how to get the right size capacitor with my zip lock
bags and aluminum plates? I really need to know this.
                                                       The Young coiler
                                                        Drew Murray
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