[FwdX: [TCML] High Primary Q]
bartb at classictesla.com
Fri Dec 28 18:21:20 MST 2007
I posted this to the TCML in early December but didn't receive a reply.
I've kept it around but have been busy with other stuff.
Thought I would repost and see if anyone has any disagreements or
It's not highly discussed on the list except in generalizations. So, as
I did this little mathematical analysis, I was surprised myself.
> Hi All,
> How high does the primary Q have to be? Reason I ask is I don't think
> it's as high as assumed and I include myself in that initial assumption.
> I was looking at Rac and Rdc in primary's this weekend and came across
> an interesting find. Rac is amazingly high in the primary and
> culminates into a rather low Q. How low? How's the 50 to 100 range
> sound excluding proximity effects.
> For example, 8.5 turn primary with 1/4" tubing. Length = 789.1cm,
> thickness is .254cm, and equivalent height if shaped into a ribbon is
> 1.995cm (using ribbon strip calculations).
> Rdc = p*length/cross sectional area
> p is resistivity in ohm per cm = 0.000001678
> Rdc = 0.000001678*789.1/(.254*1.995) = 2.61 mOhms
> Rac = length*sqrt((p*pi*u*f)/ht)
> p = resistivity in ohm per cm = 0.000001678
> u = relative permeability of annealed copper = 0.000001256629
> f = frequency = 229106
> Rac = 789.1/sqrt((0.000001678*3.14*0.000001256629*229106)/1.995) =
> 688.3 mOhms
> Q = sqrt(L/C)/Rt = sqrt(0.000025669/0.0000000188)/(.00261+.6883) = 53.5!
> I am only looking at a significant portion of impedance but haven't
> included surge impedance which in my particular coils case is 37.3 ohms.
> So, where is the high Q? I can't find it.
> Take care,
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