Re: Wire Losses
Subject: Re: Wire Losses
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Wed, 29 Nov 1995 00:37:00 GMT
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Quoting Chip Atkinson:
> Do you know how twisted stranded wire compares to braided in
> terms of loss?
When I use stranded wire in Tesla coil applications I have always
looked for DC power cable or other wire that has a very slight
twisting, if any, of the strands. I have avoided avoided using
stranded wire with a great deal of twisting in RF applications
(read Tesla coils). It just seems to make sense.
> Also, should I then replace the braided ground wire for my
> secondary with something solid or stranded?
This is one that also makes perfect sense, yet I was still very
surprised at the difference a good ground strap makes to the
overall secondary Q. The ground strap needs to be smooth strap.
I have found that 50 foot rolls of 4 inch wide aluminum flashing
can be purchased cheaply and is very high Q. The cost per foot is
much, much, less than 1 inch tinned copper braid, and it works
markedly better in this application.
I regret that I drew up my COILBLD.GIF diagrams to show some
braided ground strap connected to the smooth ground plate at the
base of the coil. I should have diagramed and stressed that
smooth strap be used for the ground path, but I was just
becomming aware of this issue at the time I created the GIFs.
The advantage of using smooth strap over braid can be measured
with a scope and frequency generator. Disconnect the ground strap
from the RF ground, leaving one end connected to the base of the
coil. Then place the entire length of the ground strap on an
insulator. Plastic sheet, plastic grocery bags, etc., may be used
to insulate the ground path from earth, concrete, metal, etc..
Connect the input from the freq. generator to the far end of the
ground strap (away from the coil) and adjust until you reach near
a flat line on the O'scope indicating resonance in the coil.
Without changing the settings or turning off the warmed up freq.
generator and scope, disconnect and remove the braided ground
strap. Replace the braided strap with one of smooth aluminum
flashing. Run the replacement strap on the same insulated path
that the braided strap was measured on. Reconnect and look at the
scope. I tried this several times with different straps, every
time I made the substitution to smooth strap I was able to get a
flatter line on the scope. The flatter the line when grid
dipping, the higher the coil Q. This really does work towards
improving the secondary coil Q.
The same relative experiments can be performed while grid peaking
the tank circuit. I routinely swap caps of different types,
change tap leads, reconnect & reroute tank circuit components,
etc. while looking at the relative Q on the scope. Like Malcolm
states; if you look hard enough, you really can see when things
are not going right. When firing new or modified tank circuits I
discharge ALL of the caps (bypass too) on the HV side of the
power supply, then touch all of the wiring, components, and
connections, feeling for hot spots indicating problems with
excessive loss and resultant reduction of tank circuit Q.
Sometimes problem areas and lossy spots are found at power
(indicated by excessive heating) that are missed with the scope.
For those of you guys out there without scopes, do not despair!
We spent the money and experiment with stuff like this so you
don't have to. If you use common sense, and follow the constantly
improving construction methods we outline here, you won't be
missing out on too much.
... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12