Re: [TCML] 2 beginner questions

[Yurtle Turtle <yurtle_t@xxxxxxxxx>]

The only conductor that gets warm on mine is the lead running to my tap. I forget what size it is, but it's probably around 12 or 10 AWG. I have some thicker automotive stereo wire scraps (that someone paid WAY too much money for), but never got around to swapping it out, as the wire on it gets warm, but not hot. So at even runs at 15 to 25 kVA, we're probably only talking about a few watts.



________________________________
 From: Jim Lux <jimlux@xxxxxxxxxxxxx>
To: tesla@xxxxxxxxxx 
Sent: Tuesday, May 15, 2012 9:31 PM
Subject: Re: [TCML] 2 beginner questions
 
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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