First Coil Up and Sparkin'

From:  D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent:  Sunday, June 28, 1998 11:57 AM
To:  Tesla List
Subject:  Re: Re First Coil Up and Sparkin'

to: Gary

Three 500 pf TV "doorknob" caps in series off each NST bushing seems to
work well.  This gives a total of 167 pF at 60 kV.  This works without
robbing too much power as you mentioned.  This should not be used with a
pole xmfr as it will resonate the secondary winding and damage it.  With a
pole xmfr a resistance of 100 Ohms at 2 kW should be used (lots of 100 watt
units in series and parallel).


> From: Tesla List <tesla-at-pupman-dot-com>
> To: 'Tesla List' <tesla-at-pupman-dot-com>
> Subject: Re First Coil Up and Sparkin'
> Date: Saturday, June 27, 1998 9:40 PM
> ----------
> From:  Gary Lau  27-Jun-1998 1803 [SMTP:lau-at-hdecad.ENET.dec-dot-com]
> Sent:  Saturday, June 27, 1998 5:43 PM
> To:  tesla-at-pupman-dot-com
> Subject:  Re First Coil Up and Sparkin'
> >Q's: What type of wire should I use from cap to primary.  I'm currently
> >using 10g copper but if the wires get close to each I get corona (?)
> >wires.  I have plenty of large 2g and 4g stranded wire that is more
> >insulted but thought I had read that this stranded wire presented losses
> >also.
> If you're getting corona, the problem isn't the gauge, they're just too
> close.  #4AWG stranded is a fine choice for a coil your size.  I use
> uninsulated copper straps.  The tank components should be laid out such
> that wiring is as direct and short as possible.
> >NST Protection: Currently, I've bypassed my protection.  Chokes wound
> >22awg on 3" x 4" cores scavenged from ancient flyback transformers.  I
> >some arcing problems and I'm now sealing with 3M IVI spray sealer.  Has
> >anyone tried this product?  I originally had a 500ohm 65watt on each leg
> >transformer and 1000pf of ceramic caps across NS, I received a tip I'm
> >I didn't blow NST and should connect caps from NST to ground??  Both
> >What size caps best?
> I suspect the arcing was from the wire to the core, I doubt a spray
> sealer will help here.
> I think the tip you refered to was mine, where I pointed out that your
> caps, rather than being in parallel with the resistors, should be from
the NST
> terminals to (RF) ground.  Your parallel configuration is no more likely
to blow
> the NST as with no protection network at all, just that it was doing no
good in
> that configuration.
> The protection network should have a cap from each HV terminal to RF
> Then a series resistor (what you had are fine) from each HV terminal to
> main spark gap.  And also, a safety spark gap, from each NST terminal to
> ground (in parallel with the bypass caps).  Some coilers additionally use
> choke in series with each resistor (either side).  The jury is still out
> whether this is a good thing.
> The value of the bypass cap is generally a few hundred pF on each side of
> the NST.  The more pF, the more effective is the low pass filter it
> forms.  However, the larger it is, the more power is wasted.  Most don't
> realize it, but with each 60 Hz half-cycle, you charge two caps to your
> NST's voltage:  The tank cap, and the bypass caps.  When the main gap
> fires, the tank cap's energy goes into the tank and into sparks, but the
> bypass cap's energy goes into the series resistors, doing nothing useful.
> If the bypass caps (two in series) had the same value as the tank cap,
> fully half of the transformer's power would be wasted as resistor heat.
> In your case, the two 1000pF caps in series are 500 pF and represent 10%
> of your tank cap's value, so about 10% of your NST's power is being
> here.  You might try series-connecting some for 500 pF per side.
> Regards, 
> Gary Lau
> Waltham, MA USA