RE: question

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tb3-at-att-dot-net>

Hi Dave,

I have also just started using a potential transformer, 
and it is a very different animal from the NST.  I have 
yet to find a MOT for balasting, but was able to use a 
15/60 neon transformer in the same mannor as described 
by Godfrey.  I have a clamp-on current meter to monitor 
see what is going on.  The current limited at about 10 
A.  

I was not satisfied with this somewhat low current, and 
unwilling to pile up a lot of NSTs to ballast the PT.  I 
had just picked up a 500 foot roll of 12 gauge wire from 
the local Home Depot (less than $20), for making a 
magnifier.  I wondered how that would work for 
ballasting.  It measured about 0.9 ohms DC resistance, 
and I don't know the inductance.  But I hooked it up in 
series with the PT anyway.

With 120 V on the PT + 12 gauge roll, and the PT output 
shorted, the current limited at about 25 A.  Getting 
excited, I hooked it up to a variac and a Tesla coil.  
It works great.  The current hits about 15A when the 
variac is at about 75%, and the TC output is looking 
better than ever.  I did notice that the ballast is a 
BIG electromagnet, and tends to pull metal and other 
wiring toward it.  Hehe.

I'll try to measure the inductance sometime, and also 
try a 500 foot roll of 14 gauge wire.  But this setup is 
working pretty good for now.  

Having metering on these setups is a must.

Terry Blake
> Original poster: "Loudner, Godfrey by way of Terry Fritz
<twftesla-at-qwest-dot-net>" 
> <gloudner-at-SINTE.EDU>
> 
> Hi Dave
> 
> I hope you are using a ballast on your transformer, otherwise the
> transformer will be ruined by excessive current. Place a choke in series
> with the 120 volt primary. The inductance of the choke will limit the
> current flow through the primary during the short circuit at the spark gap.
> You can make a choke by shorting the secondary of a mot (microwave oven
> transformer) and placing the primary leads in series with the primary of the
> potential transformer. When the secondary leads of a mot are connected
> together, some of the inductance in the primary is cancelled, allowing a
> pretty good and safe current to flow to the potential transformer. If you
> want more current to flow to the transformer, then connect the primary of a
> second shorted mot in parallel with the primary of the first mot. More mots
> can be added in this way, but eventually the inductance of the choke will
> become so low that excessive current will flow to the potential transformer.
> One or two mots should be sufficient. You will have to accept whatever
> inductance is supplied by your choke. Some people have chokes custom made
> for a particular power supply, but this approach is very expensive. At
> http://www.pupman-dot-com, much information can be obtained by entering the word
> ballast into the search engine. 
> 
> For short periods, your potential transformer can be run at twice it rated
> level. Your transformer can really putout a lot of current, making it a very
> dangerous transformer. I would not attempt to place a hand held fluorescent
> tube near the secondary of a tesla coil while using such a powerful
> transformer. The tesla secondary could become connected to the tesla primary
> by a streamer. This could allow lethal currents from the primary tank
> circuit to enter your body. Depending on the situation, you could be
> electrocuted. Then there will be no more research coming from you concerning
> your spiro secondary project. Such demonstrations should be left to the
> seasoned professional, who take a calculated risk by considering EVERYTHING
> that could go wrong. 
> 
> Godfrey Loudner      
> 
>  
> 
> > -----Original Message-----
> > From:	Tesla list [SMTP:tesla-at-pupman-dot-com]
> > Sent:	Friday, February 01, 2002 8:47 PM
> > To:	tesla-at-pupman-dot-com
> > Subject:	RE: question
> > 
> > Original poster: "David Thomson by way of Terry Fritz
> > <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>
> > 
> > Hi Godfrey,
> > 
> > I fully understand what you mean by the Potential Transformer is not
> > current
> > limited.  I put it on my Tesla coil today.  The spark gap looked more like
> > an arc welder.  My single thoriated tungsten, magnetically quenched,
> > static
> > spark gap just couldn't handle it.  I've been working all day to build a
> > spark gap to handle the power.  Fortunately I have eight heavy duty
> > military
> > electrical contacts made with pure silver rings and some kind of
> > non-corrosive, hard electrode.  A preliminary test with this new spark gap
> > on my 15KV NST showed a 100% increase in spark length on my secondary
> > terminal.
> > 
> > Yes, the impulse level does seem a bit low compared to others I have seen.
> > But I don't intend to see anything over 50KV in the primary so that should
> > be OK.  I'm hopeful that this higher current can be put to good use in my
> > coils.
> > 
> > Tell me some safety tips concerning the secondary terminal when the
> > amperage
> > is increased.  I haven't worked with a high current transformer on a Tesla
> > coil before.  Will it still be safe to hold a fluorescent tube to the
> > terminal to draw off sparks?
> > 
> > Thanks,
> > 
> > Dave
> > 
> > David Thomson
> > dave-at-volantis-dot-org <mailto:dave-at-volantis-dot-org>
> > 
> > 
> > -----Original Message-----
> > From: Tesla list [mailto:tesla-at-pupman-dot-com]
> > Sent: Thursday, January 31, 2002 5:58 PM
> > To: tesla-at-pupman-dot-com
> > Subject: RE: question
> > 
> > 
> > Original poster: "Loudner, Godfrey by way of Terry Fritz
> > <twftesla-at-qwest-dot-net>" <gloudner-at-SINTE.EDU>
> > 
> > Hi David
> > 
> > My mistake that I thought you were writing about a primary. You certainly
> > have a potential transformer, not a neon sign transformer. A potential
> > transformer is not current limited, but a NST is current limited. A
> > potential transformer is used to monitor the voltage level of a
> > transmission
> > line. High voltage is reduced to low voltage for connection with a volt
> > meter. The 50kV peak could mean that the insulation can withstand a
> > momentary transient of 50kV. Seems a little odd, usually the impulse level
> > is 150kV.
> > 
> > Godfery Loudner
> > > -----Original Message-----
> > > From:	Tesla list [SMTP:tesla-at-pupman-dot-com]
> > > Sent:	Thursday, January 31, 2002 8:18 AM
> > > To:	tesla-at-pupman-dot-com
> > > Subject:	RE: question
> > >
> > > Original poster: "David Thomson by way of Terry Fritz
> > > <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>
> > >
> > > Hi Godfrey,
> > >
> > > >In your original mailing, you wrote like you were talking about the
> > > secondary. But a secondary is not flat,
> > >
> > > Mine is.  I wound a 27" diameter flat spiral secondary out of 21 gage
> > > wire.
> > > I'm doing several experiments with flat spiral secondaries.  You can see
> > > some of my work with smaller flat spirals wound with three parallel
> > wires
> > > at
> > > my web site www.tesla-coil-builder-dot-com.
> > >
> > > >What you call a potential transformer just might be a high voltage
> > > testing
> > > transformer.
> > >
> > > I'm learning a bit more about this transformer today.  I may have been
> > > wrong
> > > in stating it was DC output.  The transformer schematic on the cover
> > shows
> > > a
> > > positive and negative terminal with arrows supposedly indicating the
> > > direction of current.  But this may simply mean that one terminal is
> > > intended to be on the ground side and the output may be AC after all.
> > > It's
> > > an older transformer made by Westinghouse and I have much to learn about
> > > it.
> > > One person has suggested to me that it is actually an old style neon
> > sign
> > > transformer.  It has a winding ratio of 120 to 1 and there is nothing
> > > indicating there is a rectifier inside.
> > >
> > > If this is correct, then I have an old 14.4KV neon sign transformer
> > rated
> > > for 50KV peak.  The label clearly identifies this transformer as a
> > > Potential
> > > Transformer.  Perhaps the two are synonymous?  Are there any experts on
> > > this
> > > list who can clarify this terminology?
> > >
> > > David Thomson
> > > dave-at-volantis-dot-org <mailto:dave-at-volantis-dot-org>
> > >
> > >
> > >
> > 
> > 
> > 
> > 
> 
> 
>