[Fwd: [Tesla-2] High Power Factor Neon Transformers]

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

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

I didn't notice that Jim's post was crossposted to the main list... here's
the answer to his last question

From: Bert Hickman <bert.hickman-at-aquila-dot-net>
X-Mailer: Mozilla 4.75 [en] (Win95; U)
Subject: Re: [Tesla-2] High Power Factor Neon Transformers
Date: Sun, 11 Nov 2001 09:18:00 -0600


Jim,

This is admittedly a little hairy. Your planned system (15 kV/120 mA and
0.0212 uF MMC) is "sized" so that the tank cap will resonate with the NST
at the incoming (60 Hz) mains frequency. In this case, charging current
delivered by the NST will be significantly greater than the faceplate
rating since some of the inductive limiting of the shunts is being
partially counteracted by the capacitive load of the tank cap - the system
"looks" like a resonant series RLC circuit. If allowed to proceed, series
resonance between the NST's leakage inductance and tank capacitance would
quickly increase the NST's output voltage and current to the point where
your NST or tank cap's insulation will break down, short circuiting one or
the other. When resonant with the tank cap, a 15 kV NST can easily (try to)
generate voltages greater than 100 kV... but the NST or your MMC will fail
long before this point is reached. In order to use resonant charging
reliably your main (or your safety gap) must ALWAYS fire before your NST or
tank cap breaks down. 

Assuming your gap fires reliably, you'll get more gap firings every half
cycle of the incoming AC waveform, since the tank cap's recharging current
is now greater after each gap firing. Since the internal leakage inductance
is a function of the NST's winding and core/shunt geometries, the resonant
charging effect is virtually independent of any PFC approach you may take
on the primary side of the NST. And despite what you may read on some of
the fringe Tesla Coil and Free Energy sites, Tesla Coils always obey the
Conservation of Energy Law. 

The bottom line: the tank capacitance you're planning to use will work just
fine and will extract close to maximum power from your bank of NST's
irrespective of whether you use internal, external, or NO PFC at all. Just
make sure that your safety gaps are always in place and adjusted properly!

Adding PFC simply brings the voltage and current of the power supplied from
the incoming power mains more closely into phase, reducing the peak current
drawn from the mains for the same coil output power. If you've already got
high power factor NST's, use them. If not, order low power factor NST's and
add external PFC caps and adjust the amount of PFC capacitance for lowest
primary current. Note: if your mains can handle the uncorrected current
drawn by your system, PFC is not necessary. In any event, your coil's
performance will be unaffected by any PFC approach you choose to use.

If you want to delve more deeply into some of the theory, you may wish to
read the Ballasting, AC Resonant Charging, and Inductive Kick Effects
sections of Richie Burnett's excellent web page:
http://WWW.RICHIEBURNETT.CO.UK/tesla.shtml

Best regards,

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com

Jim Mora wrote:
> 
> Thanks Bert,
> 
> You shed much light on  PFC, though I am still concerned about the output "P"
> due to power correction and the somewhat PFC loss effect of the .0212 uf MMC
> tank. I must be missing something here.
> 
> The tank caps are tuned to resonate with the xformer effectively that
approach
> nearly eliminating the shunts? Yes?
> 
> Without getting too deep into this, will the recommended tank capacity still
> allow for maximum power transfer (1800 Va), or did I buy a second boat anchor
> to lug outside? I guess I'm lost in the -J plane, but I believe in the
> conservation of energy theory ;-).
> 
> Know that I am running a dedicated circuit from my over designed main. And
> since I live in California, we live with candle power most of the time:-)
I can
> afford to draw excess power now and then.
> 
> The bottom line here is: given there is loss across the dual PFC's, will my
> effective power to the coil be halved and will the tank resonate at
optimum? Be
> patient with me, I started with vacuum tubes and my razor is becoming
dull :-)
> 
> Jim
> 
> Bert Hickman wrote:
> 
> > Hi Jim,
> >
> > In order to limit short circuit current, all neon sign transformers (NST's)
> > use internal magnetic shunts (small core laminations) to shunt some of the
> > magnetic flux, reducing the degree of electromagnetic coupling between the
> > primary and secondary windings. These shunts have the effect of adding
> > significant "leakage inductance". This means that the primary winding of an
> > uncorrected NST will appear to be very inductive - and the incoming current
> > and voltage will be significantly out of phase with one another.
> >
> > "Power Factor Corrected" or "High Power Factor" NST's use an additional
> > internal winding and HV AC
> > capacitor to help compensate for much of the inductive effect, bringing the
> > primary current and voltage more closely into phase with one another,
> > thereby reducing the peak current demand of the transformer. A corrected
> > NST will typically consume half the input current of an uncorrected one
> > (i.e. half the volt-amperes) while delivering the same output power (in
> > watts). This can be seen in Transco's Tube Footage Chart - an uncorrected
> > 15kV/60mA transformer will pull 900 volt-amperes (VA) on the primary side,
> > while a High Power Factor NST will only draw 464 VA. Although a 15 kV 60 MA
> > transformer will deliver 15 kV at 0 mA or 60 mA at 0 volts.. the current
> > limiting function prevents it from delivering 15 kV AND 60 mA at the same
> > time. That's why you'll never actually get 900 VA out of a 15/60 - only
> > about half that, irrespective of whether you use PFC or not.
> > See Transco's chart at:
> >    http://www.transco-neon-dot-com/tfoot.htm
> > BTW, some fairly good explanations about NST and Ignition transformer
> > design and behavior can be found on France's web site at:
> > http://www.franceformer-dot-com/faqsearch.asp
> >
> > Many coilers add external power factor correction capacitors across the
> > primaries of non-corrected NST's to achieve a similar reduction in incoming
> > current. However, when you add your MMC tank cap to the secondary side, you
> > also get a degree of power factor correction, since the capacitive load on
> > the secondary side also tends to partially cancel the NST's leakage
> > inductance. This reduces the magnitude of PFC capacitance that would
> > otherwise be necessary on the primary side of the NST. Most coilers find
> > that they really need only about half of the PFC capacitance that would be
> > necessary if the NST were driving a non-reactive load (i.e., a luminous gas
> > tube). Since the NST designers assume the NST would always see a gas tube
> > load, a PFC-corrected transformers will tend to "overcorrect" in Tesla Coil
> > use. While this will likely not cause any significant problems during coil
> > operation, I'd recommend buying NON power factor-corrected NST's, since
> > they're cheaper. You can always add external PFC capacitance until you get
> > the desired degree of correction. Note that it's not essential that you use
> > PFC, and doing so will not improve your coil's performance. But, it may
> > allow you to lower your coil's current demand so that you avoid popping
> > breakers or fuses.
> >
> > Good luck on your first light!
> >
> > -- Bert --
> > --
> > Bert Hickman
> > Stoneridge Engineering
> > Email:    bert.hickman-at-aquila-dot-net
> > Web Site: http://www.teslamania-dot-com
> >
> > Jim Mora wrote:
> > >
> > > Hello All,
> > >
> > > I have two paralleled Transco "high power factor" 15/60 transformers.
> > > The threads on this issue verses a "normal" power factor one seem vague
> > > at best to me. Is "high power factor" power phase correction or some
> > > change in shunting differing by manufacturer?
> > >
> > > I do know that the corrected V/I phase drops the mains draw by a factor
> > > almost 50%; but, I checked the Transco site and found that even though
> > > they are delivering (2x) 60/15 -at- .06 amps, the output "capacity" drops
> > > from 1800 to 927 VA.Hmm.
> > >
> > > If this is a result of the current / voltage phasing, what would likely
> > > be the effect of my Panasonic .0212 mmc cap bank to this adjusted VA
> > > rating and the charge/discharge and cap values be? (I also have a .01
> > > geek group bank at hand).
> > >
> > > France Xformer's site has lots more information on the input side but
> > > none on the output effects. Can someone shed some light (or bolts:) on
> > > this issue. I am nearing first light and will want to try to exchange
> > > $380 worth of the Transco's before I fire the coil.
> > >
> > > Thanks,
> > > Jim Mora, Fillmore School District, AE
> > >