[Prev][Next][Index][Thread]
Re: Archimedes Spiral Primaries-Spiral Magnifier Drivers
Hello All:
Dave Sharpe said in part:
>One additional nugget of information has appeared involving
>"spiral coils". At work, a consulting company issued a report
>of using spiral coils in a proprietary process application. One
>of the "bottom line" comments was that the optimum geometry for
>maximum Q for a flat or saucer-shaped spiral coil was when the ID
>was 1/5 the OD.
<snip>
The Radiotron Designer's Handbook has similar comments regarding maximum Q.
Unfortunately, flat spirals tend to have rather high distributed capacitance
which reduces their effectiveness as a conventional tesla coil secondary.
<snip>
>An alternative design, shared with Dr. Mark Rzeszotarski, was use
>a regular helical coil primary and a flat pancake secondary. The OD of
>the pancake secondary is grounded and the helical primary is powered as
>customary. The centerline of the pancake secondary was centered with the
centerline
>of the height of the primary helical coil. Mark indicated good results
>with such a system (Mark, jump in!)
As we all know (well, some of us!), maximum coupling is achieved if
the central axes of the two coils are in the same plane. This is not
practical in a conventional tesla coil due to arc-overs between the primary
and secondary. A flat pancake driver coil with a solenoidal primary wound
around the outside achieves the desired highly coupled geometry. I
connected the outer turn of the flat spiral to ground, and the inner turn
went to the extra coil in a magnifier configuration. The voltage rise is
rather impressive, with most of the rise occuring in the first few outer
turns of the spiral where most of the inductance for this type coil is
located. One could immerse this coil in oil for better protection. I have
not tried this. It did perform well as a small magnifier with a K value
around 0.4 or so.
Regards,
Mark S. Rzeszotarski, Ph.D.