Re: troubleshooting tesla coil (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 15 Jun 2007 14:41:16 -0400
From: Marko Ruban <Marko@xxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: troubleshooting tesla coil (fwd)

One more thing... I enclosed the cap sandwich between two quarter inch
plywood sheets.  Do you think it might get conductive at HV, or the glue
within plywood?  The cap terminals go through the plywood without any
additional insulation from it.


Tesla list wrote:

---------- Forwarded message ----------
Date: Fri, 15 Jun 2007 06:43:53 -0400
From: Scott Bogard <teslas-intern@xxxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Re: troubleshooting tesla coil (fwd)

Marko,
     I have seen this happen before, unfortunately there are a gazillion 
reasons it happens.  When I built my first coil, the spark gap fired first 
try, so I moved it (out of the living room) onto the porch, and all of a 
sudden it did not fire at all, just hummed (huh?).  I finally figured out, 
that the capacitor was acting as a dead short to the ground, try putting a 
big chunk of foam underneath it, or a stack of paper, this should prevent 
shorts to the ground.  Also (for testing purposes) close your gap until it 
is barely touching, even a shorted cap will fire a little under these 
circumstances.  My thinking is it is not you cap if you tried a different 
kind (beer bottle) my first plate cap failed also, but canning jars worked 
excellent.  Also, for the long run, look for some polyethylene, as I've read 
mylar isn't the best dielectric for pulse use.  Lastly, do this simple test, 
strip everything off your transformer, and arc it to the earth, (concrete 
floor whatever) if both sides arc, you are in business, if only one side 
does, you have a problem (I'm not sure if this holds true for solid state 
transformers like yours however, it won't hurt to make sure, as this can be 
a problem area).  I hope this helps.
Scott Bogard.


  

From: "Tesla list" <tesla@xxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Re: troubleshooting tesla coil (fwd)
Date: Thu, 14 Jun 2007 20:55:28 -0600 (MDT)


---------- Forwarded message ----------
Date: Thu, 14 Jun 2007 20:55:22 -0600 (MDT)
From: Chip Atkinson <chip@xxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: troubleshooting tesla coil (fwd)

Here's a thought.  It could be that a multimeter doesn't measure a short
because the multimeter's voltage is so low that it wouldn't be able to
jump any gap at all.  At 5500 volts, you can jump some gap so it could be
shorted out.

One way to debug that is to disconnect one of the leads from the NST to
the gap.  Put it on a wooden or non-conductive stick so you will be plenty
insulated from the current.  Then bring this disconnected lead up to the
point where it connects and see what kind of spark you get.  If it's kind
of a flaming spark you have a short.  If it's a really loud crackly snappy
spark then your cap is fine.

Try that and let us know what you see.

Chip

On Thu, 14 Jun 2007, Tesla list wrote:

    

---------- Forwarded message ----------
Date: Thu, 14 Jun 2007 19:32:17 -0400
From: Marko Ruban <Marko@xxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: troubleshooting tesla coil

Hello all

I was looking for some help on tesla coil construction, and joined this
list as a result.  Looks like I came to the right place :)

I'm building my first tesla coil, and could use some help "debugging"
it.  All of the coil parts have been assembled, according to various
recipes out on the web, but when put together, the spark gap doesn't 
      

fire.
    

I've got the circuit down to a bare minimum:  5.5KV, 30Khz NST provides
the power, spark gap connected across the transformer output leads, and
a capacitor in parallel with spark gap.  Without the capacitor, spark
gap fires just fine, with it, I just hear humming sound (I think coming
from the vibrating capacitor plates), but no spark.

Capacitor was home built, consists of 8 copper sheets separated by
      

10mil
    

Mylar insulator, roughly 8"x6" area.  Measured C is 7nF.  When DC power
is supplied (through a rectifier circuit), makes the gap fire at
intervals, indicating that cap is storing charge.  I thought this could
be my problem component, so I built a different type of capacitor (beer
bottle salt water, 800pF), but that didn't change a thing.  Neither
capacitor is shorted out, according to my multimeter.

Is there any definitive way to test the capacitor for faults?  Am I
missing something else?  What could be going wrong?

Thanks, for any thoughts you can provide on the subject.

Marko




      


    

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