Re: aluminum primary coil AC resistance

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com> 


Aluminum's resistivity at RF frequencies is poor and will kill the Q factor
of your primary LC circuit.  It can be used but is poor engineering.  Use
copper --- much better and more peak current into your sec circuit due to
higher peak current in the pri.

If you measure the peak pri currents while the coil is operating with a
storage scope you will see the difference.

Dr. Resonance

Resonance Research Corporation
E11870 Shadylane Rd.
Baraboo   WI   53913
 >
 > The primary resistance was limiting the amount of power my DRSSTC could
put
 > out, so I built
 > another primary that was supposed to have a much lower resistance. I built
 > it out of 6" aluminum
 > flashing, and used two layers spaced 1/8" apart. Each turn is separated by
 > 1/4" and it has 10
 > turns. The ID is ~7"
 >
 > Here are some pictures of my new primary coil
 > www.hot-streamer-dot-com/chunkyboy86/newprimarytop.jpg
 > www.hot-streamer-dot-com/chunkyboy86/newprimaryside.jpg
 >
 > The DC resistance measures about twice as high as I calculated for pure
 > aluminum, but at 4.9
 > milliohms, it is small enough. The AC resistance of the primary is 0.25
 > ohms! The skin depth at
 > 60khz is 0.013", so the 0.01" thick aluminum should have pretty uniform
 > current distribution. I
 > thought that it may be due to eddy currents in the two layers, so I tried
 > using one layer. I got
 > pretty much the same resistance.
 >
 > I ran the coil with no secondary, and was putting out 600watts. I then
 > checked the temperature of
 > the coil. The inside turn was the hottest, the next one out was not quite
 > as hot, and so on. The
 > outer turn was at room temperature.I was thinking that the inside turn
 > could be shorted, but I
 > didn't see any short. I can't figure out why the inside turns would be
 > getting hot while the
 > outside turns remain cold, can anyone else?
 >
 > =====
 > Jimmy
 >
 > _
 >
 >
 >