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Re: ARSG Questions



Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Adam,

Nice Schematic! So lets see, you've got 240 Vac 1-phase coming in to a 56A Powerstat double-stack (balanced) feeding 2 filters. Looks like you paralleled all the filter inputs? Something I haven't done. You then have TVS's across the pig inputs and everything after the pig is mostly normal (except the arrestor which David used in his designs, most don't use). I noticed the arrestor is 18.6kV. Is that it's breakdown voltage? I wonder if the arrestor is giving you problems (I suspect you already pulled it out of the circuit temporarily to check).

Wow, looks like you and I have an identical 3-phase drive system (although your RSG is much prettier than my own and your driving more power than I am). I do the same POT adjustment using the analog adjustment. It's been quite a while since I ran the coil, but I seem to remember 340 bps as ideal for my coil, however, I had more fun running it than paying too much attention to details. I just loved the ability to "rev it up"! That motor is new and a nice one (compared to others of identical specs I tested; nice tight bearings; I think it was a Baldor, same motor I'm running now). It was used temporarily for testing for a short period, but almost zero life on the motor.

Is the sucker gap helping? Seems it might hinder performance. The sucker electrodes will take the full brunt of each RSG break and will likely heat up at high powers (lower power levels probably ok). I haven't had the same problem with my gap and the reason (IMHO) is that I'm running only about 5 KVA on that coil as limited by my wimpy variac ballast with deteriorating brushes. I think you are simply seeing a condition of running high power and more than the gap can take for it's size with the available break changes you can make at will.

Unfortunately, this weekend will be spent on work (bread and butter work). I designed an H-Bridge Dual Controller for two 20A, 24Vdc motors using PID control for synchronization. All works well but only at half the frequency (optocoupler issue). So I'll be excluding myself from Tesla stuff for a couple days to deal with the issue. I had to design this in 1 week, so I threw parts at it, literally (thankfully, I chose a good controller chip; HIP4081A). On the down side, this was all schematic with zero testing as it was mostly surface mount devices. So today, I got a taste of what happens when you don't get a chance to proto the design. I was lucky I think as this is an easy problem.

Ooops, sorry to ramble.
Take care,
Bart



Tesla list wrote:

Original poster: Yurtle Turtle <yurtle_t@xxxxxxxxx>

Hi Bart.

I'm glad to finally have this thing up and running.
With very little tuning and much tweaking to go, I hit
7' on my second day, at 200 volts and around 25 amps.
I've been working on this thing since 2003! I ran it
once two Halloweens ago, but had a gap meltdown:

http://www.hot-streamer.com/adam/bigass_coil/Meltdown.jpg

I not only melted pvc, but solder as well.

When I first started modeling this coil with either
JavaTC or FanTC, I seem to recall a minor upgrade was
requird, as my coil was a little outside the norm as
far as aspect ratio. But you got it fixed and it
pretty much nailed my tuning points.

I occasionally hear my welder thumping, but never
noticed my pig doing so.

Here's my rsg, before I mounted the motor I got from
you:

http://www.hot-streamer.com/adam/bigass_coil/srsg.jpg

It's a 3,600 rpm 480 bps TTR srsg seen here:

http://www.ttr.com/rotary_spark_gap.htm

It claims to be good for 15 kVA. I got it from David
Rieben. I tried running my coil srsg style, but
decided to go arsg. I originally ran the srsg motor
with one phase of the three phase vfd, and it kinda
worked, but the vfd wasn't real happy with the phase
imballance. So I bought your 3 phase motor and had the
hub line bored (no turning back now) and added the
1725 rpm motor.

http://www.hot-streamer.com/adam/bigass_coil/rsg1.jpg
http://www.hot-streamer.com/adam/bigass_coil/rsg2.jpg

Excuse the poor pics, as I just took them in a dark
garage with no flash or tripod. Since I've heard
several people state that they couldn't run their
rsg's with both sets in series, I set mine up to use
just one set. Maybe I sould try the other set in
series, though I'll have to cut down my motor mounts
to accomodate the larger motor.

As to the VFD, I have it setup with a pot which is
currently set for 45 - 150 Hz! It seems happiest (at
current power level) around 70 - 80 Hz. I'm curently
using five sets of two 37667's, so I have 75 nF. I'd
like to try removing 15 nF at a time, while adding Hz,
to see if adding more pri H helps my gap issues.

Here's my schematic:

http://www.hot-streamer.com/adam/bigass_coil/schematic.pdf

Adam

--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: "Barton B. Anderson"
> <bartb@xxxxxxxxxxxxxxxx>
>
> Hi Adam,
>
> Glad to hear your getting the coil up and running
> with the VFD! I've
> read your posts at work but haven't had time at home
> or work to
> respond in the past few days. I originally used a
> resistor in my pig
> (2.5 ohm, really big 3KW resistor). My reason for
> using it was the
> pig would thump at high power levels. The change in
> current in the
> core causes the thumping and it is a very
> discernible audible low
> frequency noise. I only heard this with my 13"
> diameter coil, but
> quit using it with my smaller coils as the thumping
> was no longer
> there. I'm not sure this will help with your issues
> at the gap. The
> resistor is there to limit the speed of change of
> current in the core
> (slow the change down) as a fixed value. I don't
> realize a
> relationship for the gap issue. I mention this
> because it's probably
> wise to go down some other avenues first.
>
> I suspect the gap itself is the issue. I personally
> use as close a
> spacing as possible. I don't remember in the posts
> if you described
> your gap, but if not, that would maybe help (or
> picture would be
> cool!). I personally don't like a static gap in use
> with a rotary
> when I consider an ideal case. A static gap is a
> band aid for a
> rotary that needs to be beefed up for the power.
> But, due to cost and
> onhand components, it is often the best coarse of
> action for the time
> because as rotary requirements for power increase,
> the cost goes up.
>
> Anyway, I was just thinking if we could see your
> ARSG, than maybe
> something might stick out to those who have run into
> similar problems.
>
> Take care,
> Bart
>
> PS, are you adjusting speed with the 0-10V analog
> input or are you
> using presets? (just curious).
>
>
>
>
>
> Tesla list wrote:
>
> >Original poster: Yurtle Turtle <yurtle_t@xxxxxxxxx>
> >
> >Thanks. I just added another 30 Hz to my VDF setup,
> so
> >I can go from 30 to 150, with a 1725 RPM motor.
> That
> >will allow breakrates of up to 575. At current
> power
> >levels, I get better length at around 70 - 80 Hz,
> >which is around 280 bps. I started this coil back
> in
> >2003 if I recall. While I say I've played with gap
> >spacing some, I kinda concider this weekend to be
> >first light, as I was unable to get the rsg to
> "keep"
> >the spark, as my safety gaps always took over. I'll
> >keep playing and will look for a big resistor to
> use
> >in line with my welder. I'vwe always read about
> some
> >folks needing resistive ballast, but I thought that
> >was just to keep their welder happy. I have two
> slide
> >chokes that I plan on using instead of my welder.
> Do
> >they also need the resistive ballast, or is this
> more
> >of a welder ballast issue?
> >
> >Adam
> >
> >--- Tesla list <tesla@xxxxxxxxxx> wrote:
> >
> > > Original poster: FutureT@xxxxxxx
> > >
> > > In a message dated 3/25/07 8:53:32 PM Eastern
> > > Standard Time,
> > > tesla@xxxxxxxxxx writes:
> > >
> > > >Original poster: Yurtle Turtle
> <yurtle_t@xxxxxxxxx>
> > > >
> > > >I've noticed a number of large coils use arsg's
> > > with
> > > >no problems, while others seem to need a static
> gap
> > > in
> > > >series with their arsg. Mine seems to be the
> > > latter.
> > > >Does anyone know why some need this and others
> > > don't?
> > >
> > >
> > > Adam,
> > >
> > > This is an interesting question and I think it's
> > > affected by
> > > various factors.  Factors such as coupling,
> > > ballasting,
> > > transformer voltage, cap value, power level,
> > > mechanical
> > > dwell time, rotary gap spacing, electrode speed,
> > > etc.,
> > > could affect this.
> > >
> > > With a high break rate, a small amount of
> ballasting
> > > is usually needed to obtain sufficient power
> > > throughput.
> > > This small amount of ballasting makes the gap
> appear
> > > more like a short to the transformer when the
> gap
> > > fires.
> > > The gap may try to power arc, or it may try to
> > > re-fire
> > > again while the electrodes are still aligned
> which
> > > will
> > > cause inefficient operation and heavy current
> draw.
> > > This especially true with a slow rotary speed
> and
> > > with
> > > wide diameter electrodes.  This becomes even
> more
> > > true
> > > when the rotary is slowed down for lower break
> > > rates.
> > >
> > > Making the gap spacing wider could possibly stop
> > > some
> > > of the problems above and make the static series
> gap
> > > un-needed.  With some coils, a very close gap
> > > spacing
> > > is needed to obtain steady firing.  So
> > > experimentation
> > > has to be done to find the best spacing.  In
> your
> > > case
> > > I see you tried various gap spacings, so some of
> the
> > > other
> > > factors above may be affecting your coil.
> > >
> > > Richard Hull used to use some resistive
> ballasting
> > > along
> > > with the inductive ballasting to dampen unwanted
> > > thumping
> > > and resonances in the power transformer at high
> > > break rates,
> > > with a small amount of inductive ballast.
> > >
> > > Coils with large caps running at 120 bps or so
> > > generally
> > > use larger amounts of inductive ballast, so they
> may
> > > have
> > > less need for a series static gap in series with
> the
> > > rotary.
> > >
> > > Regarding running 4 series rotary gaps, this
> also
> > > depends
> > > on many of the types of factors mentioned above,
> > > such
> > > as voltage, resonances, etc.  I think Ed Wingate
> > > uses
> > > 0.020" spacing or so on his 12 point series
> rotary
> > > gap on
> > > his magnifier.  If four rotary gaps are used,
> the
> > > spacing
> > > may need to be closer than when using 2 gaps.
> For
> > > my
> > > small coils such as the TT-42, I have to run the
> > > rotary gaps
> > > very close with just a few thousands of an inch
> > > spacing.
> > > That coil uses only two series rotary gaps.
> > >
> > > I remember Bob Svangren saying that one of his
> coils
> > > ran well with a rotary with 6 electrodes, but
> would
> > > not run
> > > well with 8 electrodes.  I think it was because
> he
> > > had to
> > > slow the speed when using 8 electrodes, and it
> may
> > > have
> > > made the dwell time too long.  This may have
> caused
> > > re-firing of the gap while the electrodes were
> still
> > > aligned
> > > (two firings per electrode presentation).
> > >
> > > John
> > >
> > >
> > > >My 10" coil used this gap:
> > > >
> > >
> >
>
>http://www.hot-streamer.com/adam/bigass_coil/srsg.jpg
> > > >
> > > >modified to use a 3 phase 1725 rpm motor for
> > > between
> > > >120 and 460 bps. I've tried various rsg gap
> > > spacings,
> > > >but adding a series static sucker gap makes it
> run
> > > >very smooth. Unfortunately, my coil is so loud,
> I
> > > have
> > > >to limit my runtimes to several hours a week.
> That
> > > >limits my ability to make modifications and try
> > > them
> > > >out, so I'm trying to leach info from folks who
> > > have
> > > >already figured this out.
> > > >
> > > >Has anyone had any luck running all four gaps
> in
> > > >series on an ASRG similar to mine?
> > > >How about two sets in parallel?
> > > >What gap spacing are most folks running on
> their
> > > ASRG?
> > > >For folks running a series static gap, what
> type,
> > > >number of gaps, and total spacing have you
> found
> > > work
> > > >best?
> > >
> > >
> > >
> > >
> > >
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> >
> >
> >
> >
>
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