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RE: Sizing capacitors



Original poster: "Terry Oxandale" <Toxandale@xxxxxxx>

I used 3/32" (different diameters are available) flux coated welding rods inserted snuggly into a PVC tube, and then epoxied them in place (poured epoxy into both ends). It warms up a little at 5 kva, but worked very well for its purpose.

________________________________

From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Mon 6/19/2006 3:19 PM
To: tesla@xxxxxxxxxx
Subject: Re: Sizing capacitors



Original poster: "Nick Andrews" <nicothefabulous@xxxxxxxxxxx>

For a decent-size core, you could go down to Home Repot or Lowe's or
any lumberyard (or a construction site) and get some steel form
pins.  They are ~1/2" dia steel and smooth, unlike rebar and fairly
cheap.  Plenty long to rig up a control mechanism for adjustment, and
can be cut shorter easily with a hacksaw.

Nick A





>From: "Tesla list" <tesla@xxxxxxxxxx>
>To: tesla@xxxxxxxxxx
>Subject: Re: Sizing capacitors
>Date: Sun, 18 Jun 2006 14:39:42 -0600
>
>Original poster: "Dr. Resonance" <resonance@xxxxxxxxxx>
>
>
>
>Did you dip each rod into an insulating varnish before bundling to
>reduce eddy currents?  If not, did the core get hot?
>
>This sounds like a reasonable solution to an expensive problem.  I
>will also try it perhaps with 1/4 inch steel rods.
>
>Dr. Resonance
>----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
>To: <tesla@xxxxxxxxxx>
>Sent: Sunday, June 18, 2006 1:27 PM
>Subject: RE: Sizing capacitors
>
>
>>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 ===
>> >
>> >
>
>