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Re: [TCML] Primary selfC
Paul, Gary,
You will have to explain how any other type of primary can be made out of
ribbon ? I am not sure a vertical or otherwise is even physically possible ?
coupling is an issue, in order of 0.05K. Cannot rework the primary in any
way if it increases the coupling.
Factors for consideration... Firstly, This is a DC based coil. The initial
bang is DC, low resistance of the primary to pull the current. Also
inductance is a factor here also. My caps do not seem capable of 800amp
pulses, so this has been reworked to 250amps (hence the reason for this
thread in making sure nothing else alters in using more turns)
Second, the possible real problem, 2mhz frequency, large surface area is
needed, for this copper strap probably is not the best choice (eddy currents
etc), though its not as simple as you think. I could use copper tube and
maybe gain better HF efficiency, though the resistance of the primary would
be many times higher on the DC level so it would greatly reduce my initial
DC pulse which set everything in motion in the first place.
Overall, I went for a primary which would give the best figures for the DC
part of the circuit. The 2mhz part will probably not be very good, though
the cap is 31Joules capable so even if 50% loss it still will have enough
efficiency to overcome a lot of these "problems".
Going back to resistance, if you go from 0.002ohms to 0.015ohms you pretty
much kill 100% of the bang energy, food for thought for sure! Again the
reason for my re-working my primary. The system does work as is, with a
single turn, though I fear the caps DVDT/DVDI ratings are not what I assumed
them to be. They were supposed to be good caps, though the ratings are not
published. Most good caps should cope with 20A/uS though I am going for
2A/uS , works out at 250amp pulse over 800amp pulse.. so most caps should be
happy with 250amp pulses... I think the worst caps were those rolled yellow
ones which everyone is/was using, maybe 50A/uS ? don't recall offhand!
Unfortunately, its all compromise every time (isn't it always!) The low
voltage does not help matters much, I should have gone for 1KV pulses then
it would have helped get pulse time down and resistance wouldn't be so much
of a problem... but as with all new designs, many of them won't work! Though
at least when I build the MK2 design I will have *hopefully* ironed out all
the bugs by then ;-)
Chris
----- Original Message -----
From: "Lau, Gary" <Gary.Lau@xxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Sunday, July 27, 2008 4:10 PM
Subject: RE: [TCML] Primary selfC
I would agree that a spiral ribbon is not the best choice for a high-Q
primary. When I made AC resistance measurements on several different
primary conductors, all of the same inductance, a 1" x .03" copper ribbon
showed a slightly higher AC resistance than a coil of 1/4" Cu tubing, over
all frequencies of interest, despite having less than half of the tubing's
DC resistance. I attributed this to eddy currents; not sure how this
differs from proximity losses.
http://www.laushaus.com/tesla/primary_resistance.htm
Regards, Gary Lau
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of Paul Nicholson
Sent: Saturday, July 26, 2008 5:26 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Primary selfC
This compact ribbon primary is proving to be interesting. The
high turn-to-turn capacitance is turning out to have a
non-negligible contribution to the internal capacitance of
the coil, which as a result, affects the coil's effective
inductance and will lower the resonant frequency. By how much?
I hope to be able to estimate this, or at least point the way.
I'm brewing up a more thorough reply which goes into the matter
in some detail. I'd like a few more days to work on it so that
I can try to adapt some of the tssp software to this type of
coil - not something we've looked at before.
Meanwhile, have the proximity losses of this design been
considered? If high Q is a design priority, would a helical
ribbon rather than a spiral ribbon not be a better proposition?
--
Paul Nicholson
--
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