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On 12/18/14, 9:30 AM, John Paul Grippa wrote:
Hello All, It has been a while since I have posted, but do read all
of the emails on a regular basis. I am in the process of source
materials for my first BIG Coil and plan on using a ribbon primary.
Does anyone know how to calculate what thickness and height the
copper stip would need to be when building a primary of this type?
once the strip is more than 4 or 5 skindepths thick, it's mostly
mechanical issues, because not much current is flowing in the middle of
the strip.
You can go as wide as you want (subject to mechanical properties) to get
the DC resistance down.
copper (resistivity 1.62 microohm-cm) at 100 kHz has a skin depth of
0.008".
If you compare to, say, 3/8" copper tubing (which has an OD of 1/2"..)
and a wall thickness of 0.025 to 0.050".. most of the current isn't
flowing in the inner wall.
OD of 0.5" is a circumference of about 1.5", so the "effective cross
sectional area" is 0.008*1.5 = 0.012 square inches.
A 1" wide ribbon that is 0.020 thick has a perimeter that is about
2",and since the current flows mostly in the outer 0.008", the AC
resistance is probably less than 1/2" OD tubing.
10 mil (0.010") and 2" high is probably comparable, too.
As
you know, the price of copper stip goes up drastically when you move
from say 10 mil to 20 mil or from 1" to 2'' in height. I was hoping
to use the cheapest 100' stip that would sustain the current. I have
seen many setups that were using stips of 2" or 3" in height and 30
mil thickness. Is this really necessary? Currently, I have a 10 kVA
piggie (courtesy of the amazing John Freau) just waiting to be put
into action. I am not sure if I will be using all 10 kVA, but would
rather build a primary that can sustain the power I have available in
case I decide to do so. Thanks for all of your help! Best Regards,JP
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