Fwd: nobody knows whos maggie at fla teslathon?

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

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


>Resent-Date: Sun, 21 Sep 2003 12:38:29 -0600
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>Date: Sun, 21 Sep 2003 12:24:10 -0600
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>Subject: nobody knows whos maggie at fla teslathon?
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>Original poster: "colin.heath4" <colin.heath4-at-ntlworld-dot-com>
>hi all,
>         i take it nobody knows whos coil that was at the fla teslathon then?
>im surprised with it being such a magnificent coil.
>oh well thanks anyway
>colin
>

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Shad (Sundog)
G-5 #1373
The Geek Group www.thegeekgroup-dot-org
"Ever stop to think, and forget to start again?"
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