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Re: power v energy measurements, was Re: SSTC does 10 foot sparks
Original poster: "John Couture" <johncouture-at-bellsouth-dot-net>
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
Secondary voltage = 392 x .5 = 196 KV
If I connected an ammeter to the ground wire of the secondary coil I would
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.
----- Original Message -----
From: "Tesla list" <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
> 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"
> 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,
> 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
> The energy input can be in only one form and that is watt seconds
> 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
> 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
> 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
> 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
> an approximation of the real power. As Steve said, he is drawing less
> 20 A at 240 volts, so the apparent power must be less than 4800 VA, and
> real power cannot exceed the apparent power, so it must be less than 4800
> (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
> 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
> in to and out of the reactive compenent, and part of it gets wasted as
> 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
> >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
> >of energy.
> >I agree with you that to compare energy and power is utterly useless.
> >is like
> >comparing apples and oranges. This thread discusses the comparing of
> >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
> >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
> >factor). Steven was commenting on power factors.
> >John Couture