RE: Sizing capacitors

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>

Hi Dr. R, et al,

I made 2 of your 3" X 20" last year using 18" of #10awg solid wire and mild
steel 3/8 rods of this length cut by a local steel supplier(fairly cheap)
and using two part marine epoxy. I shook them around abit but they were
always vertical. Surprising, the core moved fairly easily after 1/2 hour of
set, no very freely inside the 3" sch 40 tubes. I drilled a bolt through the
bottom of 18" to prevent them from slipping and mounted them vertically
inside a network punch down cage. Hmmm. Very adjustable core.. and fairly
cheap to make. Pics and inductance and minor temp rise @ 10KW  with static R
240v are in the archives or maybe Terry will need to bring them back. Thanks
Terry, I want to use these on the fourth.

Regards to all,
Jim Mora

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Saturday, June 17, 2006 8:50 PM
To: tesla@xxxxxxxxxx
Subject: Re: Sizing capacitors

Original poster: "Dr. Resonance" <resonance@xxxxxxxxxx>




I'm presently experimenting with some neat 2 x 2 x 12 inch supercil
M6 grain oriented cores to develop a straight core type of current
limiter for MOTs and PTs.  The final design may contain 200-300 turns
of #12 or # 14 AWG wire but should provide good series current
limiting reactance for PT powered systems.

I also have made up some 3 x 3 x 20 inch long straight cores that I
will be winding up with some #10 AWG for current limiting testing
with pole pigs. The bad news is these cores are not cheap due to the
high price of this special steel --- over $200 per core!

Dr. Resonance




>Original poster: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>
>
>Thanks Dr. R., Terry, this is great stuff!  I'm
>finally beginning to understand "LTR" and "STR" :-)
>For my DC (non-resonant-charging) project, as Terry
>mentioned, I ought not to have to worry about
>transformer/cap resonance, which is goodness, I
>suppose!
>
>Now I'm left to play with ballasting the little PT for
>200-300VA.  I had originally thought about using some
>of the adjustable 5k 100W resistors I have all over
>the place, but what a waste!  The problem with using a
>PT this small is that a pair of 3kV 30mA NSTs would be
>smaller, especially after adding a ballast.  Still,
>the little PT looks "cool", so I'll see what I can
>come up with :-)
>
>Thanks again,
>Aaron
>
>
>--- Tesla list <tesla@xxxxxxxxxx> wrote:
>
> > Original poster: "Dr. Resonance"
> > <resonance@xxxxxxxxxx>
> >
> >
> >
> > Another interesting formulation is matching the
> > transformer to the
> > capacitor size.
> >
> > Imagine if you have a variac to adjust the voltage
> > and another variac
> > to adjust the current, ie, an adjustable series
> > inductor on the
> > primary side of your pole xmfr / PT xmfr.
> >
> > For initial testing you might set the xmfrs
> > impedance equal to the
> > impedance of the capacitor bank.  Use a climbing arc
> > to set the
> > current to a certain value, ie, perhaps 30 Amperes.
> > Knowing the 30
> > amp current value on the primary side using 220
> > volts you can calc.
> > the power in the system  The, using the 14,400 volt
> > sec xmfr value
> > you find the sec. current value.  You then use this
> > value to match
> > the capacitive reactance value and you have the
> > resonant match value
> > for the xmfr - cap bank.  Go slightly above this
> > value to prevent
> > undesireable xmfr to cap resonance, usually 1.3 to
> > 1.4 times the
> > capacitive match value at resonance.
> >
> > Now, here is where the interesting part begins.
> >
> > Set up a current meter on the primary side and
> > monitor the primary
> > amps. Increase the voltage control variac to 89-90%
> > and then adjust
> > the current control (series variac) for 25-30 amps.
> > As power is
> > applied to the coil system, at some point, you will
> > notice the
> > current actually begin to decrease even as you
> > increase the voltage
> > control variac.  In ham radio, tuning linear amps,
> > this was referred
> > to as "dipping the plate current at resonance".  The
> > current will
> > decrease as the voltage variac (power into the
> > system is
> > increased).  There is a "tuning dip" on the ammeter
> > at this point.
> >
> > This tuning point is the most efficient operating
> > point for a classic
> > spark gap Tesla coil system.  As you increase the
> > power into the
> > system the amps will again start to rise.  Slightly
> > above the "tuning
> > dip" point is the point at which the sparks will be
> > their longest
> > with a reasonable minimum of input power for any
> > given
> > system.  Longer sparks can be produced above this
> > current input
> > point, however, a lot more power is required and the
> > system is not
> > operating in an efficient mode, ie, you have
> > increased the power
> > factor above the unity point and this is an area
> > where classic Tesla
> > coils do not operate very smooth.  They become
> > current hogs and try
> > to saturate the current controller and produce audio
> > "thumps" in the
> > current and voltage variacs.
> >
> > This is what I refer to as "tuning the power supply
> > to the system"
> > and will give you a reliable indication of the most
> > efficient power
> > input (current level especially) for your given
> > system.  It's an
> > experiment worth doing at least once to determine
> > where the "resonant
> > current dip" point is for your system.  Then you can
> > adjust the
> > number of turns on your series power reactor to
> > prodvide this proper
> > level of current just as your voltage variac reaches
> > 100% on it's scale.
> >
> > Up to approx 35 Amps a single variac provides
> > voltage control for
> > this experiment while a single variac in series with
> > the pole xmfr
> > pri provides the current control.  If you are
> > running a 0.1 uF to 0.2
> > uF cap bank then you will need a dual variac for the
> > voltage control
> > and another dual variac for the current control to
> > determine this
> > tuning point.  After this experiment is conducted
> > you will know the
> > best current for your system and the second current
> > control variac is
> > eliminated and the turns are adjusted on the primary
> > series reactor
> > to provide this "dip current" or slightly above (10%
> > is usually very
> > good for performance).  This is the best way to
> > determine the proper
> > amount of current your current reactor / pole xmfr
> > system should be
> > providing to your system.
> >
> > Then, matching the impedance to determine the
> > resonant value
> > capacitance, and increase this value by 1.3 x Cres
> > and you will have
> > a very nice performing system.  Values up to 1.6
> > Cres do work but
> > they produce sparks with more of a "capacitive
> > discharge" and don't
> > seem to be as active as the sparks off a toroid at
> > 1.3 x Cres value.
> >
> > Dr. Resonance
> >
> >
> >
> >
> > >Original poster: "J. Aaron Holmes"
> > <jaholmes@xxxxxxxxxxxxxxxxxx>
> > >
> > >Thanks, Terry!  Very helpful as usual.  I suppose
> > my
> > >doubts about the transformer <==> capacitor
> > >formulation come about because it seems to me that
> > a
> > >capacitive load on the transformer is going to have
> > a
> > >crummy power factor, thus rendering the transformer
> > VA
> > >incompatible with the coil Watts value.
> > >
> > >Is that true?  In other words, to use 290nF would
> > mean
> > >200W effective power from the transformer, but the
> > VA
> > >would be higher, right?  If I'm way off, just shut
> > me
> > >up! :-))  Otherwise, what I guess I was asking was
> > >this:  How would one go about choosing a cap for a
> > >given VA, or otherwise so as to avoid exceeding
> > some
> > >rated peak current.  Again, this is a PT and
> > probably
> > >can take a few times its rated 200VA...guess I'm
> > just
> > >interested in "getting the math" instead of
> > surviving
> > >on "rules of thumb" as I have for years now.
> > >
> > >Regarding "resonance" and "DC"...duh!  My brain was
> > >obviously already in bed when I went off on
> > LTR/STR.
> > >I'd actually *love* to know how those values were
> > >computed for NSTs, etc., but if you recall sending
> > it
> > >to the list or posting it somewhere, I'll just look
> > >harder :-)
> > >
> > >Good night (for me!) -
> > >Aaron, N7OE
> > >
> > >--- Tesla list <tesla@xxxxxxxxxx> wrote:
> > >
> > > > Original poster: Vardan
> > > > <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>
> > > >
> > > > Hi,
> > > >
> > > > At 10:14 PM 6/16/2006, you wrote:
> > > > >I've built coils before using caps that were
> > > > obviously
> > > > >"way STR" (e.g., 30nF on a 15kVA pig), and so
> > never
> > > > >bothered to really understand how one sizes a
> > cap
> > > > to
> > > > >take maximum advantage of one's transformer
> > (didn't
> > > > >have room in my garage to do that with a pig
> > > > anyway!),
> > > > >but now I'm working on a coil based on a tiny
> > 200VA
> > > > PT
> >
>=== message truncated ===
>
>