Re: [TCML] 2 beginner questions

[Jim Lux <jimlux@xxxxxxxxxxxxx>]

On 5/15/12 11:47 AM, G Hunter wrote:
> Hi Jeff,
>
> Yes, it is a bit unsettling to use fat copper conductors for the various tank circuit connections and copper tubing for the primary coil,

I'm not convinced that large diameter tubing is all that necessary. 
Even with skin effect, the IR losses in the tank aren't all that high 
compared to the loss in the spark gap.

1 meter of 1.5mm diameter copper wire has an AC resistance at 100kHz of 
0.02 ohms

let's assume we've got 20 meters of wire, so we're up to 0.4 ohms total 
resistance.

The RMS current in the tank will be roughly sqrt(Q) times the RMS output 
of the transformer.

So, for a 60 mA NST, and a Q of around 10, we're looking at an RMS 
current of about 200 mA.  0.2A into 0.4 ohms is not even a watt.

You can also look at it by looking at the peak current, and integrating 
over a bunch of cycles.

Running some numbers with what I have handy..
A 10 turn flat primary, 1/2 inch spacing, 6 inch inner diameter, 20 inch 
outer diameter is 58.6 feet (let's just assume the 20 meters, above)

L is 37 uH
To resonate at 100kHz (which would be low) C is about 0.06 uF
if you charge C to 21 kV (15*1.4), ipk is 845 A, which sounds like a lot 
(285kW)  BUT, it only lasts for 5 microseconds, dissipating less than a 
joule.. And that was the peak.  If the Q is 10, then every cycle loses 
about 1/10th the energy, and since both energy and loss scale as the 
square of current, the next cycle dissipates 0.9 joules, the next about 
0.8, and so on...






Large diameter tubing is needed because:
a) it's easier to hold shape
b) it's less likely to have corona losses



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