Re: power v energy measurements, was Re: SSTC does 10 foot sparks

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

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

On 23 Jun 2004, at 16:54, Tesla list wrote:

 > Original poster: "Eastern Voltage Research Corporation"
 > <dhmccauley-at-easternvoltageresearch-dot-com>
 >
 > This energy stuff is just going to far.  As a power engineer who
 > designs high power transmitters, high power and high voltage power
 > supplies, and a boatload of DC-DC converters, I have not once ever
 > heard anyone make a reference to energy.
 >
 > Its all about power!
 >
 > Dan

     Absolutely agree. All the appliances I've ever come across are
rated in units of power based on a figure such as continuous
consumption (e.g. light bulbs, heaters) or maximum (peak) power
consumption (e.g. audio amplifiers) when running from a more-or-less
fixed voltage (e.g. 240VAC mains). I find nothing confusing about
such ratings. For one thing, it tells me what fuse ratings should
apply.
     The power consumption of a Tesla Coil inevitably varies but
knowing that one can obtain several strikes of a certain length over
some nominated period of time without popping a breaker of a
particular current rating is the figure I'd consider relevant and
useful. I once made a statement about sparklength/energy rating, a
move I left behind years ago after developing a much deeper
understanding of the dynamics involved. The passage below reads like
a supreme exercise in obfuscation to me.

Malcolm


 >
 >
 >  > Sean -
 >  >
 >  > You do not have to agree with me to be right. As I mentioned before
 >  in the > past I have used the word "power" incorrectly. This is very
 >  easy to do and > it occurs in todays literature all the time. For
 >  example power cannot be > consumed. This is why electric power
 >  companies do not sell power, they
 > sell
 >  > energy. Some coilers have said that the utility "demand charge" is
 >  selling > power. This is not correct. The demand charge is a rental
 >  charge for large > transformers and related switchgear. > > "How do I
 >  propose to use energy?"  There are many possibilities. However,
 > I
 >  > believe the best way to compare Tesla coils is to do it the energy
 >  way,
 > not
 >  > the power way. I will give an example using a small coil I built
 >  and
 > tested.
 >  > I don't have a SSTC to make a comparison  but I know there are many
 > coilers
 >  > who have both types who could easily do the tests and make the
 >  comparison. > > The tests consist of finding the TC input energy by
 >  connecting a wattmeter > to the input of the TC. This will give you
 >  input watts per second
 > (joules).
 >  > You then turn up the variac so you have 120 watt seconds input and
 >  adjust > the spark output for a continuous 120 sparks per second. You
 >  will then
 > have
 >  > 120 watt seconds / 120 sparks per second giving you  "one joule per
 >  spark" > or "spark inches per joule of enrgy". I did this for my
 >  small TC and > obtained 8.25 inches per joule. If you perform this
 >  test with with any
 > small
 >  > SPTC or SSTC you will have a fair energy comparison of the Tesla
 >  coils. > Of course the 120 sparks per second would have to be changed
 >  to the actual > number per second. > > As I have mentioned in the
 >  past this leaves a lot to be desired and I am > open to all
 >  suggestions. When larger coils are tested you will find that
 > the
 >  > "spark length per joule" is much shorter but there is a good reason
 >  for
 > this
 >  > which can be discussed later.
 >  >
 >  > This test also gives you some other interesting numbers about your
 >  TC. For > example with my coil I found the energy in the 12" toroid
 >  (about 13 > picofarads) was 1 joule per spark. This gave me >
 >    Secondary voltage = .5 x sqrt(joules/Cs) >
 >           = .5 x sqrt(1joule  / 13^-12) >           Secondary voltage
 >  = 392 KV at 100% eff. > I assumed the secondary voltage eff was about
 >  50% so the secondary voltage > was >           Secondary voltage =
 >  392 x .5 = 196 KV > > If I connected an ammeter to the ground wire of
 >  the secondary coil I would > get >            Secondary current =
 >  joules/voltage = 1/196000 >             Secondary current = 5.1 ua >
 >  Note that this is the average (RMS) current in the secondary of my
 >  small > coil. The actual peak current would be much greater. If I
 >  found the
 > average
 >  > current by test was larger I could then find the true secondary
 >  voltage > which would be higher than 196 KV. > > You can find even
 >  more TC parameters if you use energy instead of power
 > for
 >  > rating your coils.
 >  >
 >  > John Couture
 >  >
 >  > ---------------------
 >  >
 >  >
 >  > ----- Original Message -----
 >  > From: "Tesla list" <tesla-at-pupman-dot-com>
 >  > To: <tesla-at-pupman-dot-com>
 >  > Sent: Tuesday, June 22, 2004 9:15 PM
 >  > Subject: power v energy measurements, was Re: SSTC does 10 foot
 >  sparks > > >  > Original poster: Sean Taylor <sstaylor-at-uiuc.edu> >  >
 >  >  > John, I'm not really in agreement with you, the examples I gave
 >  >  > (specifically the 30 MJ) were to illustrate that two different
 >  coils, >  > consuming vast differences in power, can be given the
 >  same "energy >  > rating".  How do you propose to use energy?  Would
 >  you like to use
 > energy
 >  >  > per bang, or energy over a certain amount of time?  Both of
 >  those can
 > be
 >  >  > translated into power.  What specific measurement of energy did
 >  you
 > have
 >  > in
 >  >  > mind?
 >  >  >
 >  >  > Any meter, when used on a TC, will have fluctuations in the
 >  reading
 > with
 >  >  > the target a streamer happens to be striking at that moment.  If
 >  a
 > power
 >  >  > meter is used, then the power will jump all over the place.  The
 >  best
 > we
 >  >  > can do is to estimate an average power, where it seems that the
 >  needle
 > is
 >  >  > most of the time, or more accurately is expected to be most of
 >  the
 > time.
 >  >  > I believe that strict energy comparisons have no place in
 >  comparing TCs >  > without another parameter to give more information
 >  (as in my example
 > cited
 >  >  > in my first post on this topic - two very different TCs with the
 >  "same" >  > energy). >  > >  > In your reply to Steve, you wrote: >
 >  > >  >               Power output can be greater than power input >
 >  >               Power is in watts, average watts, peak watts, volt
 >  amps, > etc. >  >               Energy output can not be greater than
 >  energy input >  >               Energy is in watt seconds or joules*
 >  >  > >  >          The power input can be in many forms as I
 >  mentioned in my post
 > to
 >  >  > Gerry.
 >  >  >          The energy input can be in only one form and that is
 >  watt
 > seconds
 >  >  > (joules).*
 >  >  >
 >  >  >          Power factor is involved with TC power ratings
 >  >  >          Power factor is not involved with TC energy ratings.*
 >  Why?? >  > >  > I would say all but three of these statments are
 >  false (when taken in >  > certain ways).  I would consider the three
 >  true statements to be the
 > ones
 >  >  > marked with an *.  Power output can be greater than power input,
 >  if you > are >  > speaking of peak power.  Power is not in volt amps
 >  - that is apparent >  > power.  Just power is Watts, and only watts.
 >  Units themselves cannot
 > be
 >  >  > average, peak, etc., only a quantity can.  I know this is
 >  beginning to
 > get
 >  >  > into semantics, but you state that energy only comes in one
 >  form, and
 > the
 >  >  > same is true of power.  It's always just Watts (or some
 >  equivalent
 > unit),
 >  >  > nothing else.  The power input can't be in many forms, but the
 > measurement
 >  >  > can be *represented* in a few different ways, and I think that's
 >  where
 > the
 >  >  > confusion lies.  As I said before, each representation (peak,
 >  average, >  > etc.) has it's place in each application.  For
 >  comparison purposes in
 > the
 >  >  > TC world, we'll want to be using average power for the input. >
 >  > >  > Power factor doesn't/shouldn't come in to play here because
 >  power is
 > power
 >  >  > - regardless of the power facter.  Apparent power on the other
 >  hand > (simple >  > current * voltage), will change with the power
 >  factor, given a constant >  > power.  So if we know exactly how much
 >  work is being done by a system,
 > we
 >  >  > can calculate the apparent power based on the power factor. >  >
 >  >  > For most of us, it is hard to get a good idea of what the real
 >  power is >  > because all we have is a voltmeter and ammeter, and
 >  they tell us
 > nothing
 >  > of
 >  >  > the phase relationship, and thus nothing of the power factor.
 >  All we
 > can
 >  >  > then calculate is the the apparent power and all we can do with
 >  this is > get >  > an approximation of the real power.  As Steve
 >  said, he is drawing less > than >  > 20 A at 240 volts, so the
 >  apparent power must be less than 4800 VA, and > the >  > real power
 >  cannot exceed the apparent power, so it must be less than
 > 4800
 >  > W
 >  >  > (note the unit change - Watts != VA !!!).
 >  >  >
 >  >  > Now, to make the leap to energy, well, the problem is how??  As
 >  I
 > already
 >  >  > asked, which energy did you want to measure?  Even fewer of us
 >  have the >  > neccesary equipment to measure energy directly (aside
 >  from the energy > meter >  > on the outside of our house).  You wrote
 >  in another email "Energy is
 > not
 >  >  > involved with reactive powers.", while it most certainly is!!!
 >  It is
 > not
 >  >  > transferred in one direction though, because it continuously is
 >  > transferred >  > in to and out of the reactive compenent, and part
 >  of it gets wasted as > heat >  > each time that happens (in the real,
 >  non-ideal world). >  > >  > Anyway, this discussion is starting to
 >  get a bit OT, if you want to >  > continue it with me, please reply
 >  off list. >  > >  > Sean Taylor >  > Urbana, IL >  > >  > >  > On
 >  Tue, 22 Jun 2004 08:29:32 -0600, Tesla list <tesla-at-pupman-dot-com>
 > wrote:
 >  >  >
 >  >  > >Original poster: "John Couture" <johncouture-at-bellsouth-dot-net>
 >  Sean - >  > > >  > >Thank you for your reply. It appears that you are
 >  in agreement with
 > what
 >  > I
 >  >  > >was recommending and that is to use energy instead of power to
 >  rate
 > your
 >  >  > >Tesla coils. You said your TC was 30 MJ which is rating your
 >  coil in > joules >  > >of energy. >  > > >  > >I agree with you that
 >  to compare energy and power is utterly useless. > This >  > >is like
 >  >  > >comparing apples and oranges. This thread discusses the
 >  comparing of > Tesla >  > >coils not the comparing of power and
 >  energy. I recommend that coilers
 > use
 >  >  > >energy instead of power to compare their coils which is what
 >  you are > doing. >  > > >  > >There are many coilers that use their
 >  wattmeters to measure several TC >  > >parameters. However, I see no
 >  problem in your using your wattmeter to >  > >measure only average
 >  watts. >  > > >  > >Refer to my reply to Steven regarding your
 >  mention of imaginary power > (power >  > >factor). Steven was
 >  commenting on power factors. >  > > >  > >John Couture >  > > > > > >
 >  >
 >
 >
 >