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Re: Magnifier Driver coil design

Original poster: Steve Ward <steve.ward@xxxxxxxxx>

Hi Terry,

I was talking to Jimmy just a minute ago and he pointed out that i
should figure out the over all coupling between all 3 coils, that is,
treating the L2 and L3 as 1 coil.  I found a formula on Antonio's
site, looked like this:

K(L1L2L3)=(KL1L2)*sqrt(L2/(L2+L3)).  I ran my original design through
there with the ~4mH secondary and got a pathetic .07 for the K!  Im
almost certian that wont work too well.

So here is my revised design:

Tertiary: 8.1"x45" winding of 46awg with a 36" toroid up top.  L is
190mH, loaded Fr is 48khz.  Im going to start off just using my
original secondary, since i *know* it will take lots of abuse for
producing long sparks.  Will look at shorter windings later when
teslathons approach at the end of summer.

Secondary: 12.25"x18", 22awg winding.  L is 55mH.  With a 17"x2.5"
toroid on top the Fr of that coil is 123khz (not that this should

Primary:  20" diameter, 9.5 turns, .5" diameter conductor, .4"
spacing.  53uH, and using a .45uF tank capacitor.  Fr 32khz.

With a K (pri/sec) of .5, i calculate an overall K of .24, which is
right where i want it.  I looked at what i had done with the little
DRSSTC magnifier and noticed that my driver L to resonator L was a
ratio of about 1:3.2.  I felt that the driver is producing a little
too much voltage, so a ratio of 1:3.5 seems about right for a start,
so that is how i arrived at the 55mH for the secondary coil with a
190mH tertiary.

Keeping the coils from arcing will be a fun challenge.  Must not have
any sharp points on my primary!  I might also look at reducing the
Bang length on my driver so that i can try running greater than 500bps
and keep the power reasonable and see if anything fun happens :-).


On 4/17/05, Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
> Hi Steve,
> I have played a "little" with tree coil systems so don't take what I say
> with much weight compared to say Ed Wingate and others who know a ton about
> them!...
> It seems to me like the third coil is pretty conventional other than its
> based is raised up and insulated for voltage clearance on the high voltage
> base.
> The voltage between the secondary and third coil is sort of a percentage of
> the top voltage roughly based on the two inductances.  You don't want that
> voltage to go too high or you will have problems keeping the secondary top
> or third coil base from arcing.  Corona rings may be needed.
> I think the primary to secondary coupling is still pretty close to say 0.2
> if you consider the secondary and third coil as one.  Since you don't want
> the secondary top voltage to be super high, you need a fairly small
> inductance with big coupling between the primary and secondary.  But don't
> worry about it "too" much.
> In general, I think just about anything will work.  Antonio has come up
> with some cool optimizations, but I think just about any three coil system
> that does not arc over in the wrong place or has some obvious "boo boo"
> will work fine.
> I still have my magnifier thing on the "to do" list, but now I guess it
> will be run with a DRSSTC too ;-))
> BTW - If you can run at 500-1000BPS without any big added work, it may arc
> further...  I am still looking into that...
> Cheers,
>          Terry