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Re: First light, and a poor performance
Thanks for all the suggestions, here's a summery, and my response to
them.
Pole pig driven systems have an enormous amount of current which has to be
quenched - static gaps by themselves won't do it. You badly need a rotary
gap
for this system.
Bert Pool
Since I'm using a resistive ballast, doesn't this limit the current to a
value of my choosing?, I have only been running as high as 4Kw because of
the system's poor performance, I would like to be running it around 1Kw,
which based on the other systems I saw at the UK teslathon in may, can be
quenched ok by a good static gap. I've been having some hassle with me
tungsten carbide gap system, I think I'll have to build an RQ gap and try
that out.
This looks pretty thin for this power level- 6 or 8mm copper tube
would probably be better.
Mike Harrison
Thanks for the comment, I do have some 8mm tube which I will make into a
primary as soon as I have time, what is the smallest bend radius that can
reasonably be made with this sort of pipe?
Your gap seems way too small for 11KV (3mm, or 0.118" (god I hate
converting))
I'd think you would want to go at least to 0.190" (.8mm spacing?? for 6)
Micheal Baumann
The gap had to be that small, I originally had 9x0.5mm gaps, but I had
to close them down one by one till the circuit fired reliably, remember I am
not using resonant charging, so the transformer has to break down the gap
directly, without any help from resonant voltage rise
Steve, I am a complete novice compared to various personalities on this
list, but why on earth would you choose a pole-pig to power such a small
coil ??
Your supply would be better suited to my proposed next coil at 11" x 40+"
Mark Finnis
I used a polepig simply because it was all I had available, and since I
am ballasting it, I can make it look like a transformer of any power rating
I want upto it's maximum, I also plan to use it to ultimately operate a coil
12"x50" or larger.
3) You didn't mention anything about airflow over your gaps. Quenching
will be nonexistent without forced airflow, and at the power levels
you're operating at, difficult even with massive airflow.
4) Don't waste your time even thinking about operating without a top load.
A 4" sphere isn't much better. Even your proposed (finite element
array?)
3x14" toroid is too small to extract good performance from a pig.
Gary lau
Airflow over them is blown by a high capacity 80mm fan, as for top load,
I chose 3x14" because it was the correct size to enable the system to meet
the LpCp=LsCs and the quarter wave resonant conditions simultaneously. What
size would you suggest?
With small and medium size systems never start with a fixed primary of
10-11 turns. You probably don't have enough inductance to bring the system
into tune. Always use some scrap wire affixed to edgewise cardboard and
use 25-30 turns with a scraped tap at each turn.
With this setup your main cap
value should be around .02 MFD (2.0 nF) for effective tuning. It sounds
like you have way too much cap for this system with a 14 x 3 toroid. The
lowest turn on the sec. coil should be at least 1 inch above the horizontal
plane of the primary coil for proper coupling -- you are way over coupled if
you have them even, and the pri-sec spacing should be at least 1 to 1 1/2
inches.
D.C. Cox
I do have enough inductance to bring the system into tune, I can clearly
demonstrate the tune point because the output falls off VERY sharply as I
move away from it, output is down by around 1/2 at a tap point 1/3 of a turn
from tuning. Thanks for the suggestion about the coupling, I'll try moving
it up, what effect should over coupling have?
Comments:
1.) Your cap is a bit small it should be around 8.75 nF, although you could
get away with it.
Why?
4.)Your coil could probably produce better results with a bigger secondary.
Try something like 6" or 7" times 24" to 30" long (winding length) plus
another 1"-1.5" on the top and bottom (no wire). Use a wire gauge that will
allow you to wind somewhere between 800 and 1000 turns. Thicker wire/low
turns
are better because you will decrease the resistance and increase the "Q" of
your coil. The coil you built would be better suited with a 60 to 120 mA
NST.
The wire gauge you used works out to AWG 23, which IS okay for the coil you
WANT to build.
I may try that at some point, I would like to get this system to produce
output of around 16-20", but I do have some more capacitance available which
I will probably use in a 6 or 8 inch coil at a later date.
8.) FORGET the 1/4 wave stuff. Alas, another poor soul who fell (like I DID
TOO) for the old theory. Basically you will have to design your coil the
other
way around. Design your secondary first, calc at what freq it resonates
(using
Wheeler and Medhurst) and the build your primary circuit to fit.
I designed my system to meet both the resonant matching and quaterwave
conditions at once.
I hope I didn't "hit" you too hard. But you learn by doing and that means
making mistakes, too.
Reinhard
The whole reason I'm building this small system it in order to get all
the problems ironed out before going on to build the planned 12"x50" system,
cause when you get up to that size mistakes are costly and I don't have much
money.
Thanks to everyone for all the advice, I'll try to implement much of it
soon, I'm also planning on meeting up with micheal tucknott, who has kindly
agreed to let me try out my coil using some of his spark gaps so I can try
to pin down the fault. If I am able to come to any definite conclusions I'll
let you all know.
--
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