# [TCML] PFC Question (again)

bartb bartb at classictesla.com
Mon May 26 14:15:43 MDT 2008

```Hi Deano,

> Over thirty years for me. Determinants, matrices and slide rules. The closest
> we got to a computer was a teletype machine at the end of the hall. Each
> student in programming class was alloted 15 minutes computer time for the
> trimester. You wrote the program in Fortran, got your cards punched, and then
> hoped it worked. My how the world has changed.

Yipes! Punch cards! Well, I'm not too far behind. I remember those days
and we played with a punch card machine in high school. Those days form
me were DOS Dungeons and Dragon's (the beginning). I attained a
Commodore 64 and where I learned some Basic programming. I even had one
of the first laptop computers (IBM, no hard drive, only two 3.5" floppy
drives). I wonder if today's techno's can figure out how a computer
works without a hard drive? (Hint: 1 floppy has DOS, computer has RAM,
other floppy for saving data).

> The problem though, is that those types of transformers do not give you much
> to work with. You can measure the resistance (at least of the high voltage
> winding) with an Ohmmeter, but it would take a very special meter indeed to
> measure the inductance. It can be done, but it is not as easy as just
> switching the Wavetek 27xt to inductance and sticking the test leads on to
> the high voltage terminals.
No, digital meter's won't do it. You have to measure current in the
short and opened conditions. The meter will never be able to magnetize
the core.
>  You will get a reading, but it will not be
> anywhere near the actual value because the core will not be magnetized. And
> while dividing the kVA rating by the output Voltage will give short circuit
> current for a NST or OBIT, a PT or pig is a different animal. There is a way
> to calculate the short circuit current for such transformers based on the
> percent impedance rating, but my 5kVA pig with 1.6 percent impedance
> calculates out to something on the order of 15kA short circuit. Transposing
> that back to the other side (primary and secondary are reversed) gives 250A.
>

Yes, exactly! And there in lies the rub. My 10kva pig is 1.6 percent
also. Healthy beast!

> My understanding of the terms STR and LTR may be in error, of course.
> As I understand it, STR means the capacitors value is less than that of a
> resonant size cap. And LTR means that its value is greater. STR more
> reactance, LTR less reactance,  than that of a resonant size cap.
>
Perfect. That is exactly the descriptions as intended.

> My understanding of resonant size is that value of capacitor that will
> resonate with the inductance that it shares the circuit with, at the
> frequency of interest. Power factor of unity. X(sub-L)=X(sub-C).
Correct.

>> If one was to use
>> PFC's, they would at least have a capacitive range in the vicinity
>>
>
> Call it an absolute maximum value. Range between that and zero.
>

Yes, in non-ballasted transformers like PIG's and PT's. For those that
are already ballasted (NST's), it may not be max.

>> Maybe label it "maximum" PFC value. And for self-ballasting transformers only.
>> I do not know.
>>

I'll probably get rid of it altogether.

>> One thing though, I think where some folks might get in trouble, is when they
>> want to design a Tesla coil around a transformer (PT or pig),  and they
>> insert some number into the box called "rated mA". For example, lets take my
>> 5kVA pig. If I use 5000/14400 or 347mA, it gives me 4997VA, 41499 Ohms,
>> resonant cap 60nF, PFC 230uF, static LTR 95.9nF, and  SRSG LTR 166.7nF.
>>
>> If I use the actual measured short circuit current with the ballast (15/60
>> NST, dual primaries in series for 240V operation, both secondaries shorted)
>> in place, of 85mA, it gives me 1224VA, 169412 Ohms, resonant cap 15.7nF, and
>> PFC of 56uF. Also static LTR 23.5nF, and SRSG LTR 40.8nF.
>>

Yes, but the program specifically says to insert the "rated" current.
Not measured in a shorted or opened configuration. The outputs which
follow are based on the rated data as set by the manufacturer.

>> Anyway, I think there may be more folks running resonant or LTR with their
>> pigs or PTs than are aware. Just a guess.
>>
I don't think so. Costs and energy across the gap are the reasons. I
think most are STR. Some might try LTR, but were talking huge cap sizes
and severe bang sizes across the gap. Highly unlikely and very expensive
in both cap and gap costs.

>> I wonder if users would rather not have PFC listed? Deleting stuff is
>> easy. I have no problem getting rid of it.
>>
>
> Ultimately, it IS you, and not the users, who will have to make that decision.
>

Yes it is. I'll likely remove PFC output on the next update.

> I will say, however, that I am quite impressed with JavaTC. Over the years I
> have avoided it because of the name, "Java"TC. I have nothing against the
> language, and have done some simple programing in it before. A decade ago. It
> is the VM that is such a resource hog that I do not like.
Oh believe me, I hate it also in more ways than I could express!! I feel
I could write a book on why not to use JavaScript, but the alternatives
are no better.

It does serve a purpose as it allows anyone in the world to use it
without specific software and it is client side. Really, the only "real"
thing I dislike is non-compiled code (from a speed perspective). Well, I
also can't stand DOM issues, but that's part of the pain I guess.

> Then the other day
> (or week) when Kris was working on that mini twin thing, and my numbers from
> Ed Sonderman's spread sheet did not match yours from JavaTC. The old tried
> and true spreadsheet had never failed me before, so I thought "I'll have a
> look."
Ed's spreadsheet was the beginning of Javatc. Javatc once mimicked the
spreadsheet. But of course, it's culminated into some FEA equations not
possible in a spreadsheet. But, this was necessary if we wanted to
account for object proximity and their effects.

> Anyway, I put
> the numbers for my Medicine coil in there just to see how well it handled a
> small weird coil. To my suprise, it found the sec. operating freq. right on
> the money. 680kHz, right smack on top of KONO AM in San Antonio. It also got
> the primary frequency as being too low, obvious in operation due to the ring
> of short (1.5") streamers around the toroid when operating. Looks more like a
> crown of thorns than a gas burner. If I put an eXacto knife, or screwdriver
> up to it, however, I can pull a single streamer out to 6.5" with ease. It
> also said the tank cap was too large and the gap would never fire. That is
> true too. It has a half wave rectifier and takes about three cycles to pump
> the cap up to firing voltage. Runs at about 20 PPS. Very weird coil. Also
> drew a very nice picture of the coil, to scale.
>
> So, as far as getting someone else to write a TC program, you are probably out
> of luck. You have set the bar too high. Just one of the costs of excellence.
>

Thanks for those Kudo's. Someday someone will (I hope). I'm not a
programmer, I'm an engineer. So, this Javatc thing I do is difficult for
me and it takes a lot of work and time to get it right. My work
experience as far as programming is in PLC's and Microchip PIC's (and
even that is very limited). My main function at work is to design
"whatever" is needed. I do a lot of CMOS gates and source driving. This
week I'm designing a brushless DC motor drive for an application. Those
are the kind of things I do regularly. This Javatc stuff is something
quite different and I'm sure there are better people in this world for
this type of work. Someday, someone will step up and put me to shame (I
long for that day!).

Take care,
Bart

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