[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: TC efficiency, was Math help...
Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>
John,
Comparing air streamer length versus input power is a useful way to compare
relative performance between systems. And, I suppose one could define Tesla
Coil "efficiency" as spark length versus input power or as incremental
power vs incremental spark length. In any event, by looking at the results
of many coils, one might conclude that the "efficiency" of the process of
converting increments of additional wall plug power to increments of spark
length gets progressively worse as we go to higher power levels. Thus far
we mostly agree... although efficiency usually compares output power vs
input power as a percentage; it's not clear that incremental watt/length is
a valid measure of efficiency.
Where we do disagree is in the reason(s) for this falloff in "efficiency"
at higher power levels. The measurable "electrical efficiency" (i.e., going
from the input to the output terminal) will likely tend to be greater for
larger systems than smaller ones for many of the reasons mentioned by other
posters. By following good design practices we can minimize the effects of
these electrical losses. We have a degree of control over the electrical
efficiency of our systems, and a number of coilers have simulated and
measured efficiencies for various parts of their systems.
However, we are fundamentally constrained by physical "inefficiencies" when
we try to convert increments of additional power into increments of
streamer length. And, as we all know, this "inefficiency" only worsens as
we go to higher power levels and longer leader lengths. I've discussed some
reasons why this is the case in my previous post. The power law
relationship is ultimately inherent to the processes of streamer and
leader formation, propagation, and their "steady state" (energy balanced)
length.
In well designed systems, the dramatic "efficiency" falloff is NOT due to
dramatic increases in losses from the charging circuit, primary tank
circuit, or resonator. The falloff arises because we must expend an
increasing portion of available power in (re)heating the root and main
channel of existing leaders, and this leaves less available to further
extend leader length. Progressively more power goes into heating the
leaders instead of lengthening them.
If these incremental "losses" came from any of the TC's electrical
subsystems, we'd be "letting the smoke" out of the offending component(s)
in short order for very large systems. And increased corona losses should
be comparatively small in well designed systems. Compare pre-breakout to
post-breakout power reflected back into the primary in a well designed
system - it's clear that the power going into streamers is MUCH larger than
that lost in corona. You can't ignore the physics/behavior of sparks in
air, John. At higher power levels, more incremental power is expended as
heat - in making existing leaders hotter and fatter - than in making
leaders longer.
Best regards,
-- Bert --
--
Bert Hickman
Stoneridge Engineering
Email: bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com
Tesla list wrote:
>
> Original poster: "John H. Couture by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <couturejh-at-worldnet.att-dot-net>
>
> Bert -
>
> Refer to my post to John F. regarding the power vs spark length equation.
>
> How do you determine the efficiency of your coils?
>
> John Couture
>
> -------------------------------
>
> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Sunday, July 15, 2001 1:52 PM
> To: tesla-at-pupman-dot-com
> Subject: Re: TC efficiency, was Math help...
>
> Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <bert.hickman-at-aquila-dot-net>
>
> John C. and all,
>
> I suspect that the nonlinear power vs spark length characteristic is more
> due to mechanisms underlying streamer and leader propagation/maintenance
> than being an indicator of Tesla Coil inefficiency at higher power levels.
> It simply takes increasingly larger amounts of power to develop and
> maintain longer leaders. The current, channel temperature, and electrical
> conductivity at the root going outwards must be greater for a long leader
> than a shorter one. This helps compensate for the the increased voltage
> drop that comes along with longer leaders. This voltage drop must be
> counteracted by higher terminal voltage so that we can obtain sufficient
> far end E-fields (>30 kv/cm) to support leader propagation and maintenance
> (until we reach "steady state" balance between leader length and input
> power).
>
> While topload energy scales as the square of output voltage, our ability to
> overcome an increasing voltage drop in the leader is more a linear function
> of output voltage for a given leader conductivity. A greater portion of the
> available energy must go into heating and widening the leader root and
> nearby channel versus shorter leaders. A leader having an overall voltage
> drop that's twice that of a shorter leader will require twice the topload
> voltage, or 4X the topload energy, to achieve the same E-field at the
> leader tips. This is likely why John Freau's spark length formulas show
> length to be related to the square root of power - quadrupling input power
> doubles the length:
>
> L = 1.7*Sqrt(Power in) for a 120 BPS system
>
> A coil generating longer leaders has much "fatter" and "whiter" arc
> channels in the portion nearest the toroid, a clear indication that
> significantly more energy is being dissipated in this portion of the
> channel than for shorter leaders. The relationship has much more to do with
> the "efficiency" of incinerating air than it does with the efficiency of
> power transfer between TC primary and secondary of larger versus small
> systems. In general, larger coils should be more efficient in transferring
> power from the mains to the toroid. It's just not obvious if we only look
> at the trend of spark length versus input power...
>
> Best regards,
>
> -- Bert --
> --
> Bert Hickman
> Stoneridge Engineering
> Email: bert.hickman-at-aquila-dot-net
> Web Site: http://www.teslamania-dot-com
>
> Tesla list wrote:
> >
> > Original poster: "John H. Couture by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <couturejh-at-worldnet.att-dot-net>
> >
> > John F -
> >
> > A well known characteristic of Tesla coils is that the watts per foot of
> > spark increases as the TC gets larger. This means losses increase and
> > efficiency decreases as the TC is made larger. The range is about 200
> watts
> > per foot of spark for small coils to 2000 watts for large coils. This is
> > based on measurements that coilers make every day. Have you made
> > measurements that would indicate the contrary?
> >
> > John Couture
> >
> > ---------------------------
> >
> > -----Original Message-----
> > From: Tesla list [mailto:tesla-at-pupman-dot-com]
> > Sent: Wednesday, July 11, 2001 6:35 AM
> > To: tesla-at-pupman-dot-com
> > Subject: Re: TC efficiency, was Math help...
> >
> > Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> > <FutureT-at-aol-dot-com>
> >
> > In a message dated 7/10/01 9:08:09 PM Eastern Daylight Time,
> > tesla-at-pupman-dot-com
> > writes:
> >
> > > >
> > > >When we say the TC efficiency can be about 90/95% what are the input
> and
> > > >output conditions? Coilers talk about TC efficiencies but I have never
> > seen
> > > >any published input/output calcs. In my TC Construction Guide page
> 14-4
> > I
> > > >show a simple efficiency test I made with a small TC and the
> > input/output
> > > >calcs were shown. Have any other coilers made these tests? The test
> > showed
> > > >an overall efficiency of 56%. Larger coils have efficiencies much
> lower.
> > > >What are the input and output calcs for the 90 to 95% efficiencies?
> How
> > do
> > > >they relate to the overall efficiency? How do these 90/95%
> efficiencies
> > > vary
> > > >with TC size?
> > > >
> > > >John Couture
> >
> > John, all,
> >
> > The 90 -95% figure is only for energy transfer from primary
> > to secondary for first notch quenching, not for overall TC efficiency.
> > Many coils quench on the 3rd notch, so the transfer efficiency may
> > be around 65% in that case.
> >
> > Charging efficiency is often around 85% or so, and there's some
> > loss in the secondary. This brings the overall efficiency down
> > to perhaps 50% for the overall TC for input vs output. This is
> > ballpark.
> >
> > This issue of efficiency for small vs. large coils has been discussed
> > previously on this list. I would say that large coils are more
> > efficient than small ones, mainly because various transformer
> > % losses are lower in larger transformers.
> >
> > John Freau