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Re: [TCML] 5.25" SRSG tesla coil suggestions on improving performance



Yes, you guys are correct on the acrylic disc being dangerous, and I will rebuild it soon with tufnol or similar.  If anyone has an approx 3/8" x 6" diameter disc of the stuff, I'd buy!

Right now I do want to focus on performance, as the flying electrodes stay cool, and I see no immediate threat.

I tried to shrink the cap as you suggested by removing 3 strings from my MMC so its 131nf instead of 188nf (My specs were wrong before, its 188nf not 180nf).  After re-tuning the primary to about 3 turns, significant performance was lost.  I'll be putting the 3 strings back in tonight.  Teslamap actually suggests 470nf for 4.4kv @ 300ma, or 236nf @ 150ma for SRSG.

I do have a John Fraeu Phase controller planned, but manual adjustment is working for now.

Thanks for the info!
JJ





________________________________
 From: Phil Tuck <phil@xxxxxxxxxxx>
To: 'Tesla Coil Mailing List' <tesla@xxxxxxxxxx> 
Sent: Tuesday, August 6, 2013 9:26 AM
Subject: RE: [TCML] 5.25" SRSG tesla coil suggestions on improving performance
 

The Acrylic disc is an accident waiting to happen. Lexan is stronger BUT
still not suited for a rotor disc. G10 is what a lot use, or my favourite:
Tufnol. G10 is a nightmare to machine, while Tufnol is easy.
You have way too much capacitance, I doubt they are being fully charged,
even though you have MOT's feeding them. Less capacitance will allow more
primary turns, some (me) prefer around 8 or 9, others advocate 12 or more to
keep the losses down. (I only use 115 - 125 nF with around 7kW on a 200 bps
SRSG) SRSG are less lossey gaps so you can get away with 8 or 9 turns, if
you change to a lossey RQ gap you'll be better with more turns.
You need 0.25 inch Tungsten electrodes, but don't use the Acrylic for that
size as they will become bullets! Using a 1800 rpm motor on that size disc
though with 0.25 electrodes may well give you too long a dwell time  though,
so use JavaTC to check the design out first. 
Use a John Fraeu controller for the phase, rather than manual fiddling. The
phase varies a bit even when set up, depending on how much power your using,
so you need a bit of fine control. The coil will "sing" when the phase is
right, and have a rasping sound when it is wrong.
Look up Richie Burnett's website on using 'resonant charging' with a SRSG.
In fact have a good read of his excellent site.
Consider going to 200 bps for longer streamers.
Lastly, get rid of the Acrylic :-) or did I mention that?

Phil

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of JJ Dasher
Sent: Tuesday, August 06, 2013 2:59 AM
To: tesla@xxxxxxxxxx
Subject: [TCML] 5.25" SRSG tesla coil suggestions on improving performance

Hi all,
I'm new here.  Although I've built a few coils in my past, I still consider
myself a newb coiler.  I've never been the type to do things mathematically
perfect, and tend to wing it as I go along, which may be my downfall here.
 For the past couple of years on and off, I've been working on a 5.25" SRSG
coil to use in a Halloween display.  This is my largest coil so far.  You
can see it in action here:

http://www.youtube.com/watch?v=2P3T5zuT9DI


and pictures of the guts here:

http://imgur.com/a/0jgxR



I'd like to get some constructive criticism and advice on getting this
running better.  This trips my 20amp breaker after about 10-15 seconds of
running, so I figure about 2.2-2.6kw?  I'm currently getting 36" streamers,
which I feel are somewhat weak.  They are purple, and not very bright.
Specs:

Large old powerstat variac salvaged from power equipment.  Not sure on exact
specs, but I assume it should handle 30+amps with ease.  Wired for approx
150v boost.

Dual MOT's (pulled from 1200w commercial MWs), currently unballasted.  130uf
of PFC caps behind them.
180nf MMC cap built with 10 strings of 8x 942c20p15k-f's.  1m bleed
resistors installed.
SRSG is a 5" acrylic disc attached to a 1800rpm sync motor.  4 flying
electrodes for 120bps.  Electrodes are 1/8" thoriated tungsten.  Phase is
adjusted by twisting the motor in its mounts.
Primary is 3/8 copper tubing, slightly conical.  Currently tuned at about
2.25" turns
Secondary is 5.25" x 24" 22awg magnet wire with a couple of coats of poly.
Topload is a spun aluminum 4.5"x18" toroid.
All high current busses are 4awg stranded copper with large soldered lugs.

The next improvement I plan is to upgrade to 1/4" tungsten electrodes.  The
stationary electrodes currently glow red hot after about 5 seconds of
running, so I added a fan.
I'd love to get some bright long white snakes like I've seen from similar
size coils.  Please advise!

Thanks!
JJ

P.S.  There is normally a safety gap installed, It just wasn't in place when
I took those pictures.
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