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Re: [TCML] MMC for 4 mot SRGTC

Hi All,
I agree. With my pig coil running 0.06uF STR, I started out using a synchronous gap (120 bps, then changed to 240 bps). Worked fine, but I eventually changed over to a variable RSG and sparks were best with a bps of about 360 as calc'd by motor rpm. In my case, I have a readout for this. I never went back to synchronous operation on this coil. There is a difference however of just running a non-sync motor at it's rated speed and running a variable speed motor where one can control the speed. The later would require a DC motor or 3-phase motor (I use 3-phase).
The advantage I see with sync operation is that you have a controlled bang size and will have less missed firings, where non-sync operation will always have these. But with controlled variable speed non-sync operation, you have the ability to adjust in the bps and power throughput. This is my preference on the pig coil. I wouldn't do this with an NST (stick to sync or static gaps for the health of your NST) and the reason is that missed firings will allow the cap to charge to a higher value before the next presentation which runs the possibility of killing the NST. Of course if the safety gap is set properly, it will fire more often, and then the safety gap heats up and starts taking over as it begins firing at a lower and lower voltage. 

Take care,
Bart

David Rieben wrote:

Hi Scott, Kris, all,


I tend to agree with Scott on this issue. I've heard many of
the pro's and cons regarding synch vs. asynch and IMHO,
it comes down to a matter of preference on large, pig sized
coils although there does defonitely appear to be an advantage
to going synch with mid-sized coils driven by the limited avail-
able power from NSTs. If longer sparks are what you're after,
which is where the majority of us coilers are ;^), then the fast-
er BPS rates afforded by an asynch RSG are a definite
advantage with the much greater power throughput potential
of large non-current limited transformers, like pole pigs. Some
coilers do like to go synch with high powered coils, but from
the spark length reports of synch vs asynch with larger coils,
there doesn't really appear to be any advantage to "going synch"
with a piggy powered coil. An asynch gap is also a bit sim-
pler to construct. Also, there's the issue of securing a primary
cap of sufficient rating to run LTR with a pole pig, as an LTR
prerequisite would make for an impractically large and expen$ive
capacitor. It's a lot simpler and more practical to just go asynch
with an STR cap, utilizing a >100/120 BPS charge/dicharge cycle
of the primary cap to increase the power throughput for longer and
brighter sparks with large, high powered coil systems. Indeed, my
large coil, with a 0.1 uFd primary cap seems to like 350 to 400
BPS for the best output.
http://www.dawntreader.net/hvgroup/david/gm.html

My $.02,
David Rieben
----- Original Message ----- From: "Scott Bogard" <teslas-intern@xxxxxxxxxxx> 
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Sunday, April 06, 2008 8:51 AM
Subject: RE: [TCML] MMC for 4 mot SRGTC



Hi Gary, Kris,
I use a sync gap on my 4-MOT coil. I wish I didn't! Granted I use a ballast, but my performance is limited to about 54 inches. 4 MOTs can do much better, I've seen it. You would be better off to design yourself an asynch gap, and then the cap size really doesn't matter as much. My understanding is that using sync gaps requires a properly sized cap for maximum performance, and my cap size was picked on faulty calculations, so lesson learned, it is best to just go asynch anyway. I am in the process of designing an asynch gap, but it will be a long time until I can afford to build it with school expenses. As for using .4117 uf for a cap, my guess is that would eventually destroy the secondary, but I really don't know (I have had burnouts with .075, let alone .4 or even .12). Just a thought. There are others with more experience that can probably comment on this. 

Scott Bogard.



From: Gary.Lau@xxxxxx
To: tesla@xxxxxxxxxx
Date: Sun, 6 Apr 2008 13:18:47 +0000
Subject: RE: [TCML] MMC for 4 mot SRGTC
CC:
I have never built a MOT-based coil, so take this comment with a grain of salt, but is using a sync gap necessary? Using a higher break rate would diminish the required cap value. I think I've heard more async gaps used with MOT's than sync gaps. Maybe the same with pole-pig coils. A LTR cap there would be HUGE. 

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Kris Grillo
> Sent: Saturday, April 05, 2008 11:49 AM
> To: tesla@xxxxxxxxxx
> Subject: [TCML] MMC for 4 mot SRGTC
>
> I am putting together a 6" coil with 4 MOT power supply and a 120 bps > sync rotary > gap. I would like to run the mots wide open (no ballast). I estimated > 8400 V .5A for > the transformer output. For the MMC, JavaTC is saying I need .4117uf for > LTR! > That seems huge to me. I have 60 of the 942's for 5 strings of 12 right > now, and I > planned on doubling that to get to .1249uf before I get it up and > running, but that is > still less than resonant. I could probably swing another 84 caps to get > to 12 x 12 for > a just about resonant cap, but 336 more caps for the .4117uf value is a > little out of > my price range right now. Is it so important to run larger than resonant > cap with a > mot driven srg coil? The mots are under oil, if that matters. Any > suggestions? 
>
>
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