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Tesla!

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Packet: TYRELL
Date: 08-13-94 (08:54)             Number: 0
From: CSHIELDS                     Refer#: 36
  To: tesla-at-grendel.objinc-dot-com      Recvd: NO (PVT)
Subj: Success!!!                     Conf: (0) Email
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T>>~Last night I finally got a tesla coil to work!  I used Gary Legel's
T>>~TCBA newsletter design (with a few modifications for currently available
T>>~materials).  I was getting streamers around 18" long from the top.
T>>~Now the next trick is to get them longer.  It's been so long since I starte
T>>~to make tesla coils that I had almost decided to cut my losses and find
T>>~some other use for the transformers and capacitors that I had amassed.

That's great.  Congratulations!

T>>~got a streamer coming off the top turn of the secondary, instead of the
T>>~top terminal.  The second is that after a longish run, my circuit breaker
T>>~on the variac tripped.  When I reset it, the coil didn't seem to power up
T>>~smoothly.  As I turned up the variac, I could hear the spark gap firing
T>>~as it always has, but I would only get an intermittent streamer, and only
T>>~when the power was turned up about 75%.   Before hand, I would get little
T>>~1" hairs that would smoothly progress up to the full length as I turned up
T>>~the variac.  This last time, I would only get nearly full length streamers
T>>~in little bursts.

T>>~So, here are two questions for everyone:
T>>~1) Does any one know why I am getting streamers from the top turn?

        There could be a couple of things.  One could be that your
        discharge terminal is not large enough to pump out the voltage
        as fast as it builds up in the secondary.  Or perhaps it is
        large enough, but is too far away from the top turns.
        Another cause could be that the turns are not coated thickly
        enough with polyurethane or some other type of insulating coat.

T>>~2) Does any one have any ideas why I am getting intermittent streamers?

        Sounds like something is shorting out under load, like somewhere
        the circuit is finding ground before it should.  Make sure that
        you don't have any sharp points on your primary coil, or on any
         of the connectors in the primary tank circuit.   While you are
        at it, take a look inside your secondary coil.  It could be you
        may see tracking where it's sparking down to ground inside the
        secondary.  If it is, try insulating all your secondary
        connections with RTV where it goes inside the tube, and put a
        little plastic tube over the wire where it runs over to the
        center electrode on the inside.  Another coat of poly or varnish
        wouldn't't hurt either in that case.

T>>~Any ideas would be helpful.



T>>~>> Series: I tried it without success on two neon sign transformers.
T>>~Perhaps I didn't play with it enough.  I am somewhat paranoid about
T>>~neons because they short out so fast.
        Neon sign transformers won't work in series like that.  The
input windings aren't't designed to handle any voltage over 120v AC.  In
my coil I am using 3 neon sign transformers in parallel.  Each xformer
is 15000v, 2 of them are 30ma and the other is 60ma for a total current
of 120ma.
        A couple of things I have been told about how to protect neon
sign transformers seem to be working well for me, and I'll share them
here.
1       Arrange your circuit so that the spark gap is across the output
        of the transformers, instead of having the main capacitors
        across the transformer output.  What this does is short the
        secondaries of the transformers when the gap is closed, thus
        shorting to ground any RF kickback when it's exactly at it's
        highest point.

2       Use RF chokes on each side of the circuit before the spark
        gap.  My chokes are on 1 1/2" PVC pipe and are spacewound
        using #18 insulated hook-up wire, like 25 turns, 1/4" space
        then 15 -space- then 10-space- then the last 5 turns
        spacewound about one wire space apart.  On my coil these
        are at about 60uh inductance by the LCR meter.  And going in
        to these chokes I use a 50ohm 10 watt resistor, one for each
        choke.  This prevents setting up another resonant circuit
        between the spark gap and the output of the transformers,
        with the idea being that too much inductance in your chokes,
        or having your chokes too big, bottles up some RF voltage,
        and it circulates between the big chokes and the neon sign
        output.  This would be in addition to any kickback from
        the primary tank circuit.

So to sum it up, here's how my coil circuit is arranged:
Three neon sign xformers in parallel.  Output from each side goes to
200pfd capacitors, the other end of the caps to ground.  These are the
bypass caps.  After the bypass caps, output connects to either side of a
safety gap with a grounded center electrode.   Coming out of the safety
gap on each side is the 50ohm 10 watt resistor which connects directly
to the chokes, with the end with the most turns on the choke being
toward the transformers.  The chokes are then connected to the spark
gap, one for each side.  One side of the spark gap is connected to the
primary capacitors, the other side to the inside turn of the primary
coil.   The primary capacitors are connected in series, with voltage
coming in from one side of the sparkgap, and going out to the primary
tap lead.

I got most of this from the TCBA newsletters, and from a couple of
coil building friends who have had quite a bit of experience and have
shared what they know through E-mail and letters.

Let me know what you find about the problem with your coil.  We can
all learn from it I'm sure.

Craig Shields    cshields-at-tyrell-dot-net

If you like, you can call my BBS at 913-371-3228 where I have a whole
bunch of Tesla stuff online.  If you call, leave me a note so I can
upgrade you right away, because the call back verifier wont' work
on long distance calls.
CS
---
 ~ QMPro 1.52 ~ I'm not a complete idiot.  Some parts are missing.