Re First Coil Up and Sparkin'

From:  djQuecke [SMTP:djQuecke-at-worldnet.att-dot-net]
Sent:  Friday, July 03, 1998 9:17 PM
To:  Tesla List
Subject:  Re: Re First Coil Up and Sparkin'

Thanks for your time again Gary.  You been a big help on several occasions
and I certainly appreciate it.  Thanks especially for the bypass cap info.
The only thing I've seen on bypass caps was the reports from Terry's
website.  I doubled checked and it sure looks like he had his across the

It doesn't make sense to me that way but I'm not clear on the NST protection
concept yet so thru a little of everything in.  Actually, I've taken
everything off for the moment.  Not sure if the bypass caps I have will take
the voltage.  I've several in series and think I've got enough for 500pf per
side and WVDC -at- 15kV tested voltage is double that.  Much smaller than I'd

Thanks again,

-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: 'Tesla List' <tesla-at-pupman-dot-com>
Date: Saturday, June 27, 1998 8:40 PM
Subject: Re First Coil Up and Sparkin'

>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
>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 with
>>22awg on 3" x 4" cores scavenged from ancient flyback transformers.  I had
>>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 legs?
>>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
>terminals to (RF) ground.  Your parallel configuration is no more likely to
>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 the
>main spark gap.  And also, a safety spark gap, from each NST terminal to RF
>ground (in parallel with the bypass caps).  Some coilers additionally use a
>choke in series with each resistor (either side).  The jury is still out on
>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 wasted
>here.  You might try series-connecting some for 500 pF per side.
>Gary Lau
>Waltham, MA USA