Re: tesla coil power ?! (fwd)

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Original poster: Steven Roys <sroys@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Thu, 27 Sep 2007 18:18:52 -0700
From: Ed Phillips <evp@xxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: tesla coil power ?! (fwd)

Hi Ed,
Yes, I was very surprised when I first heard of their "new" work! They
claimed 40% efficiency (coupling?) I understand everything you wrote,
except the last sentence.
A 60 watt 120V bulb is about 240 Ohms, and that isn't a high Q load for a
LC circuit with a coil inductance in the range of 25 -50 uH. (series or
parallel) at 3.5 or 10 MHz.  I used bare #12 AWG wire (~ 2mm diam.) and
varied the coupling coefficient by the spacing, looking for "critical
coupling".  I don't know if the unloaded receiver coil Q approached 1000.
For a HV connection, the voltage obviously can be increased by increasing
the effective parallel impedance, up to a point where the unloaded Q
becomes a factor. It wasn't clear in the MIT photo that the xmit or
receiving coil had any taps or links. I guess I could use a resistor load,
which could be much higher than an incand. lamp, for higher voltage and Q.
I guess it would be cheating to come up with a high-power regenerative
receiver for high Q.
-Dave D.


	I meant tapping the lamp down the coil - adjusting the coupling of the lamp to the receiving coil.  A 25 uH inductor has a reactance of about 1570 ohms at 10 MHz if I didn't slip a decimal place so for a loaded Q of say 500 the coupled effective SERIES resistance of the load would have bo of the order of 3 ohms.  That means you'd have to tap it across the coil at a point where that would be the equivalent series resistance added to the coil. That would mean a tap point [if the turns were tightly coupled which they aren't] at about 4.5 % of the total turns.

Ed