Re: nobody knows whos maggie at fla teslathon?

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

Original poster: "D&M's High Voltage" <DMsHV.DavMcKin-at-verizon-dot-net> 

Colin, All,

I apologize for the delay.  I've been out of town most of the last 3 weeks
and the few days I was here between trips I was too sick to respond.

I would like to thank Shad for his excellent answers and then fill in the
rest of the answers to all of your questions!

Base coil (Black one in the pictures):  12" diameter wound 32" (48" form)
with 12 Ga. heavy build magnet wire for approx. 360 turns.  Painted black,
and then lightning bolts were airbrushed on.  Original run was at the 2002
teslathon when the paint was still wet - worked fine!

Magnifier (Tertiary coil on the plywood base):  12" diameter wound 42" (48"
form) with 18 Ga. heavy build magnet wire for approx. 930 turns.  One of the
pictures is of me (5' 11") standing next to it on top of the platform.

Toroid:  20" x 72" chicken wire mesh with 24 sections to help make it smooth
as possible.  One of the pictures of me repairing it after our tarp beat it
half to death on the trip up to Pensacola.  Next year all of our stuff will
be crated!

We started running the coil at approx. 35-40 amps and then raised the
current level to approx. 75 amps (made the sparks a bit hotter which you can
see in the last 5 pictures of it).  The primary is an adjustable primary
(1/2" tube with approx. 9 turns spaced 1" center of tube to center of tube,
inner diameter approx. 15-3/4").  I think it finally tuned in somewhere
around 6 turns or so.  We had it very loosely coupled (approx. 6" total),
and then started increasing the coupling (by raising the primary approx.
3-1/2").  We had to back off the coupling because the arcs from the terminal
pretty much went straight to ground and didn't do much - this is shown in
the 4th picture down from the ones in which people were standing in the cage
(we never did get it "fully coupled").  Also, the 4" of corona all around
the plywood circle (unfortunately, not visible in the pictures) and the
smoke coming off the base was too much.  So we wound up with most of the
"runs" fairly loosely coupled at approx. 75 amps (~18 KVA) - unfortunately,
quite a bit of lost power.

For overall height reference:  In the pictures on Ralph's website, there is
a 12 foot ladder that I'm pushing next to the coil for size reference (a 10
foot aluminum ladder is on the other side of the coil).  Also, a couple of
pictures down from that one you can see how low the toroid is sitting on the
coil (the bottom of the toroid is approx. 4" below the top turn of the
secondary - explanation to follow).

As far as a magnifier "design" - these coils were designed to be ran alone -
not in a magnifier "mode."  So if they hit one of the "sweet modes" it's
pure luck - not design.  We did the magnifier setup for several reasons.
One was to add quite a bit of inductance to the system so that we could run
"LTR" with a big toroid.  Another reason is so that we could make really big
sparks without them hitting the base and blowing something up (like the srsg
motor).  Lastly, is so that we can run a lot of power into a closely coupled
coil without having to worry about racing sparks at the bottom of the
secondary coil (such as in a standard setup).

Next year we're going to raise the secondary another 2-4 feet on top of the
platform and put a corona control ring (connected to the bottom of the
secondary) around it.  The magnifier coil didn't have a long enough
connection rod to properly set the height of the toroid so it sat really low
on the coil.  So we're going to raise the toroid and put a corona control
toroid on top of the magnifier secondary but underneath the large one.  This
is to provide corona control to prevent flashover down through the middle of
the coil.  We're also going to make a primary that is closely coupled to the
base coil.  Lastly, we're going to raise the capacitance to 400 nF, and add
one of our Variable Reactors for precise current control while the coil is
operating.

I'll be adding pictures to our website and making CDs with all the pictures
and movies from the teslathon as soon as I can.  I'll post to the list when
these are done.

As a heads up for next year - we're planning on having it on Labor Day
weekend again next year.  So make your plans to attend early!

Please let me know if you have any more questions!

David L. McKinnon
D&M's High Voltage




 > Original poster: sundog <sundog-at-timeship-dot-net>
 >
 > Hi Colin, All
 >
 >    Sorry for the delay, I've been busy getting moved into a new house
 > (Finally have my own garage/lab!), and Dave (of D&M's High voltage) is
busy
 > with work.
 >
 >    The magnifier has a driver coil of 12x42 (IIRC) wound with 18 ga wire
 > for ~250 turns I believe.  The tertiary is 12x50" wound also with 18"
 > wire.  The base unit has a 133nF tank cap running on a 120BPS SRSG with a
 > static gap in series with the main gap.  Input power was pretty
substantial.
 >
 >    The problem we ran into was the plywood base the extra coil was sitting
 > on.  With a few hundred KV coming off the top of the driver, we were
 > getting corona all the way around the wooden base (corona off wood = smoke
 > and probably fire).  We had to shut it down for good when the secondary
 > tracked to the base and tried to set stuff on fire.
 >
 >    At it's best, the thing was belching off almost 16' of spark.  If we
 > could have eliminated the losses of the transmission line and leakage
 > through the base and legs (the 2x4's we used as legs for the tertiary
stand
 > got tracked all the way down to the concrete), we could have gotten much
 > more spark out of it.
 >
 >
 >     As far as how impressive it was... it was scary.  I've been around big
 > coils running before, but that one took the cake.  Even with the topload
 > ~10' off the ground, we got nearly constant ground strikes, and *hot*
 > ground strikes at that.  When the streamers connected to the faraday cage,
 > you could see them trying to arc upwards from the heat.  At times, the
 > system would come into near-perfect tune and push a streamer out real far,
 > and you could feel the charge even from the "safe" distance.  (means the
 > distance wasn't too safe...)  I got sparks to the tripod I was using while
 > the coil was running.   One hit from that coil to anybody unlucky enough
to
 > be within range would be an event they wouldn't forget for a long time.
 >
 >    The tank cap is a bank of 4 strings, 3 caps in each string, of the big
 > green Chenelec capacitors that Mike Loftus
 > offered.  They're rated at 10kV at .1uF each.  3 in series comfortable
 > handles a pole pig's output. Each cap is made of reconstituted mica
(unsure
 > of internal construction), and even though we got the outside of the caps
 > hot to the touch (insides much have been scorching), we've yet to have a
 > failure.  This is with 1-2 minutes at a time runtime on the coil, with
 > maybe 3-4 minutes between runs.
 >
 >    If you're planning a coil to really kick out long sparks, I'd recommend
 > a magnifier.  It gets the output away from the primary base (a streamer to
 > the SRSG or contactor's 240V terminals is a Bad Thing(tm)), lets you
change
 > the elevation of the extra coil easily, and plus, it looks cool.
 >
 >    On a note here, this is the first time I've had the opportunity to get
a
 > pole pig powered coil running on 120BPS with a massive tank cap.  (I
wanted
 > to try .4uF at ~20KVA input for LTR operation, but we burned up the
 > magnifier's base).
 >
 >    I'm an advocate of big toploads, massive tank caps, and 120BPS
 > operation.  With all my little coils, it's given the best sparks.  And now
 > with big coils, it seems the idea holds true.
 >
 >    The advantages don't stop at longer sparks, though.  The control system
 > runs much smoother, with less bucking and thumping, and almost no
 > kickback.  ASRSG with a high breakrate can lead to nasty kickback.  With
 > the LTR operation, the controller is driven hard, yes, but the load
appears
 > much smoother to it.  Something to keep in mind -
 >
 >    The massive tank cap looks like PFC on the HV side of the pig.  It
 > throws out your power factor, so adding some PFC on the input is a good
 > idea to get the current draw back in line.  We don't see this so much with
 > small coils, because we're only using a few nF of tank C, but at over
.1uF,
 > it becomes apparent.
 >
 >     I'm still itching to see the .4uF tank cap in action.  With the top
 > voltage being a function of ratios of capacitance (and breakdown voltage),
 > it should be able to put an outrageous voltage on the topload, and have
 > plenty of current to supply the streamer with once it's formed.  Either
 > way, it's going to make long streamers.
 >
 > Hope it helps!
 >
 > Shad