Re: Gap Losses (II) Re: Primary Heating

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

Original poster: "rheidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>

As I was thinking about primary heating and the responce "that current was
every where the same" I remenbered a arc/lightning problem that was similar
if I may digress to primaty heating. At the tracking site we had 9 ea 12ft
5/8 dia nickel tiped lightning rods attached to 1 sq mile of copper net
ground plane on top the mountain to the top of each antenna tower. My job
was to replace these rods after each storm. This was a mounthy project. The
rods were vaporived from 4 in above the mount up 3 ft of rod. In fact the
lower 4 in was not dammaged only 3 ft above that was gone.The  current is
assumed to be every where the same, but only the  rod above the  base were
vaporized not the threads base mount or top 2/3 length. All that remained
was  like new and useable at lower locations. If current in the primary coil
is every where the same why is only the lower terminal point hot and why
were the lightning rods smoked near the terminal point. I think there is a
common relationship with TC arc and lightning arc. In my mind current/time
can not be the same along the 5/8 pure copper rod or the primary copper tube
     Robert  H

> From: "Tesla list" <tesla-at-pupman-dot-com>
> Date: Wed, 13 Mar 2002 19:15:01 -0700
> To: tesla-at-pupman-dot-com
> Subject: RE: Gap Losses (II) Re: Primary Heating
> Resent-From: tesla-at-pupman-dot-com
> Resent-Date: Wed, 13 Mar 2002 19:49:49 -0700
> 
> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> 
> Hi Alex,
> 
> At 07:14 PM 3/13/2002 -0500, you wrote:
>> Terry
>> Is your NST filter designed for running NSTs at 140Vac. I am assuming it is
>> by the few numbers I crunched on the MOVs but I am just checking. I don't
>> want to blow up the filter($$$).
>> Thx
>> Alex Madsen
>> 
>> 
> 
> This is a very good question.  The 1800 volt MOVs are +-10% tolerance.
> 
> http://hot-streamer-dot-com/TeslaCoils/Misc/NSTFilt.jpg
> 
> There are 14 in across the NST so the voltage range is 14 x 1800 = 25200
> +-10 % or 22680 - 27720 volts
> 
> An NST at 140 VAC in is 15000 x SQRT(2) x 140/120 = 24749 volts (21213
> volts at 120VAC).  So the MOVs are NOT designed for 140 VAC input.
> 
> Normally the safety gaps should start to fire if you set them at 120 VAC.
> 
> But lets suppose you want to play dangerously and go to 140 VAC.  The MOVs
> "might" be high enough in tolerance to take it.  You can turn the NST up to
> 140 VAC and watch carefully if they start to get hot.  The MOVs will burn
> up if they have to dissipate substantial power for an extended time.  You
> could go to 16 MOVs for a range of 25920 to 31680 but now the top end is
> almost 50% over the NST rating!!
> 
> Bottom line is, you almost have to test the MOVs for breakdown voltage if
> you want to really run at 140 VAC.  You can't just trust the component
> tolerances.  On my big coil at 140 VAC in the MOVs start to heat but not
> "too" badly.  So they are being stressed along with the NST about "right".
> 
> Of course, modifying the original design or operating at over 15kVAC voids
> the warranty :o)))
> 
> Cheers,
> 
> Terry
> 
>