Re: [TCML] Designing a Coil Around a SRSG

[Scott Bogard <sdbogard@xxxxxxxxx>]

Hi Again Brandon,
     Glad I could help!  Yes, that secondary should work fine, and yes
adding that second top load should be fine also.  SQRT of 1800= 42, so you
want between 21 and 38 inches of overall diameter, when considering
multiple toploads, if memory serves, you just sort of add the diameters, so
26+14=40.  A bit over-gunned, but it should work fairly stable with a
breakout point (if it doesn't, remove the second top load and re-tune the
primary.)  As for 240/480 etc BPS...  In theory this works great, and many
have claimed success using this, it is in fact very similar to the logic of
using a small cap and an async system.  I never could get it to work, but I
think I know why...  Firstly in those days I didn't understand power draw,
and my crappy ballast was holding me back, not my break rate and capacitor
combo, I didn't know this at the time.  Secondly I had severe trouble
because I didn't have a good phase controller, the black light/lego system
worked, but not well enough to determine phase for a system where stuff
lines up differently (at least for me.)  I didn't do the exact calcs, but I
think you should probably be Ok with the cap size you proposed, and a
normal 120 BPS for maximum output (may want to go higher and use a smaller
cap even.)  My advice is to go to the fantastic "Java TC," load the demo
coil (unless you are already a javaTC guru!) and plug in your cap values,
and transformer specs, and play with the rotary gap designer near the
bottom of the page.  Find the BPS level by trial and error that best gives
spark length as close to or higher than the "freau ideal" as possible, and
design around that.  If you are having trouble reaching that level, change
your cap configuration a little and see if you can hit it (also pay
attention to LTR values, chances are you want that.)  And like others said,
don't over volt your cap!  Java TC can help with that also, in the MMC
calculator it has, it really is a fantastic tool!  Best of luck, let us
know what you find!

Scott Bogard.


On Sun, Mar 24, 2013 at 5:40 PM, Brandon Hendershot <
brandonhendershot@xxxxxxxxx> wrote:

> Hi Scott,
>
> Superb. I understood every word.
> I'm thinking of keeping my 3.5" x 14" 29AWG secondary and adding a 4" x 16"
> Topload beneath the existing 7.25" x 26". Do you think that would be
> enough? I can't afford much error...
>
> What do you (all) think about using 240/360/480bps and a smaller capacitor?
> Or is it 120bps in itself that performs best with NSTs and not simply a
> srsg..? Otherwise I was thinking of using 4 strings of 11 caps
> (942C20P15K-f) to get 22kV at 54nf. I know this is close to the peak output
> of my NSTs, but I need to be as economical as possible. Just how unwise is
> this?
>
> I'll do some research on machining the rotor before I ask anything about
> that.
>
> Thanks a lot,
> Brandon H.
>
> On Mar 24, 2013 8:43 AM, "Scott Bogard" <sdbogard@xxxxxxxxx> wrote:
> >
> > Hi Brandon,
> >      it looks like this post got side tracked into triggered gap land, so
> > I'll answer your questions in case nobody else has.  Ok firstly looking
> > over your proposed specs (whether or not you were asking for it) my two
> > cents...
> > 15/120...  that is some serious power for NSTs, 1800 watts worth, and
> that
> > number 1800 is the basis for lots of our calculations (if you want to do
> it
> > right, we must calculate.  -
> > 7.25" x 26" Topload...  A bit under-gunned for that wattage, you could go
> > bigger for longer sparks, or leave it that size for multiple smaller ones
> > (the quick and dirty formula for top load size is (SQRT of watts) * (.5
> > though .9) = topload overall diameter in inches (.5 being multiple
> > streamers, .9 being just one.))  I would go bigger, but I like big top
> > loads only making one streamer.
> > *- ~6" x 24" 25** AWG Secondary Coil (*subject to change(**especially
> > so))...  This is a bit over-gunned for your wattage.  It does not hurt to
> > make a bigger coil, it is just unnecessary.  For reference I use a four
> > inch coil with about 2500 watts, but I like small coils with ridiculous
> > sparks.  The tend to look a bit silly, tiny coils dwarfed by their top
> > loads, but when you turn them on, this attracts more attention to the
> > sparks.
> > Ok, the capacitance of your coil is very specifically dependent on BPS.
> > Let me enlighten you to a newbie mistake, I made for several years after
> > starting coiling, there are two systems one must "tune" in a TC.  Firstly
> > is the well now resonate systems, getting frequencies fo tank and promary
> > to match secondary and topload, everyone knows this.  Secondly, and just
> as
> > importantly (and often overlooked) is the tuning of power draw, this is
> > done with ballast (not an option as you are using NST) tank cap
> > capacitance, and BPS.  a lower bps will have long to charge, and requires
> a
> > larger capacitor, up to where your ballast can no longer allow additional
> > power to be absorbed.  I don't like synchronous for this reason, you need
> a
> > HUGE capacitor for a given power draw, it is much easier to use a high
> BPS
> > and a small cap.  But, with NSTs, synch is the lowest stress mode of
> > operation, as such, it is good to use.  With that said, you have probably
> > heard of LTR caps?  LTR (larger than resonate) is the size you want to
> use
> > for a sync rotary, as it represents the size that will fill to around
> > 60-75% capacity during operation (which if we consider how capacitors
> work
> > (namely how they charge fastest when empty) is the best place to have it
> as
> > it represents the most power transfer per second (charging higher will
> take
> > up more time than it is worth, and charging lower won't move enough juice
> > into the coil.))  You could use a "resonate" sized cap, this will give
> the
> > absolute best power transfer rate every time (the ultimate in power draw
> > tuning) BUT it will most likely fry your NSTs, as it will actually change
> > your wattage from 1800 to something higher, and require other design
> > changes as shown above.  As for how to calculate these, you can look it
> up,
> > there are resonate and LTR calculators everywhere.  Personally I don't
> use
> > nor like LTR caps, I like an external ballast, and a high BPS system, but
> > that is not an option for NSTs, as the ballast is built in.
> > Ok, onto srsg design, the easiest way is to get a surplus induction motor
> > and grind flats onto it, there is loads of info on this in the archives,
> > and others have done actual studies.  When I built my only sync gap, I
> got
> > lucky and the thing worked perfectly, but if you grind off too much the
> > motor is junk, and too little and it won't sync.  Then phase is adjusted
> > with a phase controller, or rotating the motor in its mount, you want it
> to
> > fire at the peak of the AC cycle.  To adjust mine, I taped a flourescent
> > lego to the rods and used a black light, and lined it up so the brightest
> > spot lined up with the rods (this will make more sense if you read into
> > them a bit.)  Ok, I feel like I've given you enough to chew on for a bit,
> > hopefully others will chime in as well!
> >
> > Scott Bogard.
> >
> >
> > On Fri, Mar 22, 2013 at 11:50 PM, Brandon Hendershot <
> > brandonhendershot@xxxxxxxxx> wrote:
> >
> > > Hi All,
> > >
> > > Now that I've finally gotten something out of my long overdue 3.5"
> coil,
> > > I'm already itching to start work on the next.
> > > I've decided to make the switch to a rotary spark gap and have settled
> on
> > > synchronous over asynchronous for the sake of performance and security
> of
> > > my NSTs.
> > > I want to be sure I do this coil right and plan everything out before I
> buy
> > > anything. Here are the parts and specs for what I know is going into
> the
> > > new coil:
> > > - 15/120 (4 x 15/30) NST Bank
> > > - 7.25" x 26" Topload
> > > - 0.25" x 0.25" Flat Primary Coil (Plenty long, should be enough
> > > regardless)
> > > *- ~6" x 24" 25** AWG Secondary Coil (*subject to change(**especially
> so))
> > >
> > > I've read that 120 BPS is just about the best you can get when you're
> using
> > > NSTs, so I'm going to be building the rest around that. I haven't found
> a
> > > motor yet, any specific RPM to look for? HP will vary since we don't
> know
> > > what style we want yet.
> > > I'm assuming not (you know what they say about that), but does the
> > > capacitance of the MMC vary depending on the BPS? Since it's
> synchronous
> > > with the AC waveform and firing at a single frequency I imagine not...
> > > Rather, isn't the Input watts the only determining factor? Silly me.
> Next
> > > question:
> > > Does the BPS have any influence on what the resonant frequency of the
> > > secondary coil should be? <This would be my primary concern.
> > >
> > > One more quick irrelevant question, moving from a 15/30 to a 15/120,
> would
> > > there need to be any modifications made to the Terry Filter?
> > >
> > > Thanks a bunch,
> > > Brandon H.
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