3/4" vs. 1" primary on 30 Kw system ?
From: Robert W. Stephens [SMTP:rwstephens-at-headwaters-dot-com]
Sent: Saturday, June 27, 1998 11:04 AM
To: Tesla List
Subject: Re: 3/4" vs. 1" primary on 30 Kw system ?
> From: Daryl P. Dacko [SMTP:mycrump-at-cris-dot-com]
> Sent: Thursday, June 25, 1998 7:01 PM
> To: Tesla List
> Subject: 3/4" vs. 1" primary on 30 Kw system ?
> A friend asked me to post this:
> He's designing a coil that might have up to 30 Kw input on the primary (!).
> Would there be a practical differance in performance in going from 3/4"
> to 1" copper tube ?
> The price is about double for the 1", which is why he's asking.
> C = Pi * Dia, so I'd say that resistance would go down by 25%...
> Given the losses in a standard sparkgap, I'd guess that you wouldn't
> see too much differance.
> What does the collective wisdom say about this ?
Tell your friend that the only best way is to make two primaries for
his 30 kW coil system, one out of 3/4 inch copper tubing and the
second out of one inch copper tubing. Make sure that the
center-to-center turns spacing is identical for both coils (i.e.
there will be less airspace between turns on the one inch job). Both
primaries must be matched in delivered field or the comparison test
won't be valid. Please post to us all on your findings.
I know that is not what your friend wants to hear!
Without knowing other parameters, like the diameter of the HV
resonator and how many active turns this primary is going to have,
and at what voltage will the system capacitor be charged to, it is
IMO impossible to give useful opinions on the primary conductor size.
Building a 30 kW coil can be quite expensive. Tell your friend to get some
3/4 inch OD or larger Cable TV distribution aluminum hardline coax for free
from the local cable company (anything less than 100 feet on a new
reel is pretty much useless to them). Build the first primary out of
that and see how the system goes. I'm doing exactly that now on my
own personal Big Mo' coil project. I plan to change to real copper once I have
the rest of the design down pat. When I do I don't actually expect a *huge*
difference in system performance from just this change.
Money is better spent on good capacitors and a good rotary break!
Don't forget to build a substantial topload too. A smooth 20" x 8 foot OD
doughnut sounds about right to me for 30 kW.
Robert W. Stephens
Lindsay Scientific Co.
RR1 Shelburne, ON Canada L0N-1S5
Tel: 1-519-925-1771 Fax:
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