RE: [TCML] primary & power input

[david baehr <dfb25@xxxxxxxxxxx>]

 Hi,   They do also sell  .032" Thick  x  1/2"    for $13 more for a 50' roll    . That may be worth the cost ?
 
          Thd next width up is 1" , and may be a little wide for a 12" tall   cone.  Yes, prob  about 6-7 primary turns was the idea 
 
            Lots of the old/antique  coils  I see pics of have a banded pri. , I was going for that 'look'
 
                 Take care, dave
 

> From: k.schraner@xxxxxxxxxxx
> To: tesla@xxxxxxxxxx
> Subject: Re: [TCML] primary & power input
> Date: Mon, 14 Jan 2013 15:47:25 +0100
> 
> Hello David, Jim,
> 
> ...was having exactly the same concerns about corona, as you're describing. 
> But I had no problems at all, using the copper-ribbon primaries:
> 
> http://home.datacomm.ch/m.schraner/FlatPrim_1555.jpg
> 
".
> 
> 
 Even the taps, on the narrow spaced turns (only 6mm / 
> 0.236"), didn't provoke any flashovers.
> Well David, perhaps the idea to scrap the .022" idea could be thought 
> again, especially if having a multiturn primary?
> 
> Regards, Kurt
> 
> -----Ursprüngliche Nachricht----- 
> From: Jim Lux
> Sent: Sunday, January 13, 2013 9:44 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] primary & power input
> 
> On 1/13/13 11:54 AM, david baehr wrote:
> >
> >
> >
> >
> > Hello, On a primary for my little conical sec coil , I want to
> > go with the banded type. Georgia Copper has .5"
> > wide , .022" thick copper ground strap . Would this be adequate
> > for 2 kw ?
> 
> Skin depth in copper at 100kHz is 0.008 inches.
> What you can do is think about what size tubing/wire you would use
> (circumference) and compare that to the width of your strap.
> 
> Your 0.022" thick is only 3 skindepths thick, so you could probably
> assume it has uniform current and calculate the AC resistance that way
> (resistivity * length /cross sectional area) to see if it's comparable
> to what you'd use for tubing/wire.
> 
> Certainly the strap has good cooling..
> 
> But, that's a pretty thin edge, so corona might be an issue. (and, on
> general principle, sheet metal is like a knife...cuts right through
> skin, gloves, and you don't even feel it at first)
> 
> If the edge is radiused (you'll have to do this) and has 0.011 inch
> radius, the field at 20kV would be 20/0.011 kV/inch or 1800 kV/inch.
> Considering that air breaks down at about 70kV/inch, corona is going to
> be a *significant* problem with something that thin.
> 
> With, for instance, 1/4" OD tubing, the radius is 0.125, so with 20kV
> from the NST on it, you have 20/0.125 = 160 kV/inch. While more than
> double the breakdown in air, most people don't have a big problem at
> that voltage (probably because having adjacent turns close by with a
> voltage that is a few kV different makes the overall field "smoother".
> 
> But going to 10 times the field with your thin strap is looking for
> excitement.
> 
> 1/8" thick strap might work fairly well, is still bendable, etc?
> 
> A good way to check it is to to try a trial primary with some bare wire
> of the same diameter as the thickness, before you buy your strap.. if it
> arcs everywhere or sprays corona, you know you've got trouble.
> 
> 0.022" is going to be about awg 22
> 
> 
> SKin depth calculator:
> 
> http://www.microwaves101.com/encyclopedia/calsdepth.cfm
> (copper is 1.67 conductivity, frequency is 0.0001 GHz)
> _______________________________________________ 
> 
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
 		 	   		  _______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla