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Re: Peak cap voltage, was 12kV, 30ma TC specs, 42" spark


From: 	Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: 	Wednesday, September 17, 1997 2:58 PM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: Peak cap voltage, was 12kV, 30ma TC specs, 42" spark

Jason, all,
               I paid a visit to a local neon sign company yesterday 
and had a chat about transformer ratings. I am assured that going 
beyond the peak o/c output voltage is definitely asking for a 
premature transformer failure (I haven't killed one yet in order to 
find out :) 

> From:   Jason Judd[SMTP:Jason.Judd-at-anu.edu.au]
> Sent:   Tuesday, September 16, 1997 8:33 PM
> To:     Tesla List
> Subject:    Re: Peak cap voltage, was 12kV, 30ma TC specs, 42" spark
> 
> 
> > Hi Jason,
> >  
> > > I am just starting to get good results with my 6" 15Kv 60MA setup. The
> tank
> > > capacitor is 14 nF (for 50Hz) rolled poly (two series 28 nF caps). The
> best
> > > I have done so far is 35". I am using a tripple gap system quenched
> with a
> > > microwave oven fan. What I have found is that to get the long sparks
> the
> > > gap must be made quite wide to take advantage of the resonant charging.
> > > When I got to about 12MM (1/2") the terminals from my two 15Kv 30 MA
> > > tranies started to arc to the case which is about 10MM from the edge of
> the
> > > HV insulator. I supose this is a good saftey gap and may well have
> saved my
> > > transformers.
> > > 
> > > My question is how far should I open the gap to take advantage of
> resonant
> > > charging ? he gap has never miss fired yet. It apears to me that I
> should
> > > set the gap to fire around the 30 KV mark. I'm not game to do this
> because
> > > my caps were not designed with this voltage in mind , but in the future
> > > they will be.
> > 
> > What are your transformers designed to survive? You can always get 
> > big sparks from neons if you push them.
> > 
> > Malcolm
> > 
> > 
> 
> Malcolm,
> 
> What do you mean what are my transformers desighned to survive. How can I
> tell. I surpose when one fails I am at the limit ;-). They are rated at
> 15Kv 30Ma each. The peak voltage would be about 21 KV. Are you telling me
> (or trying to say nicely) that I am headed for trouble on this path ?

21kV should be fine (sounds like the 1/2" gap :)  If unsure, set the 
gap to fire with nothing connected to the transformer output. In neon 
service, the transformer output is not sustained at this voltage 
however.
    I managed to bludge a couple of old units for home coiling. They 
will also put failed tar-filled units aside for me. Definitely pays 
to be friendly with the locals :)  I also had a look at their 
bombardier setup. The transformer weighs about half a ton and has a 
current rating of 800mA and output voltage of 20kV (RMS I think). I 
was drooling. I jokingly suggested I should bring my big coil down 
and run a power feed from the transformer to a setup outside the 
building. Perhaps they might let me one day.
     A final note on using neons: I checked the merits of transformer/
primary cap resonance more thoroughly last weekend (without setting 
the gap too wide). The coil emitted a pleasing 100Hz buzz while 
running but I got the best sparks slightly off-resonance. The output 
ionization appeared too steady for extra streamer growth while 
resonant.

Malcolm