Hello Doug,
Not counting the tiny VTTC (0.5 inch discharge) that I made in 1969, I must admit that my first coil was a very large one (8.6 inch secondary diameter) powered by a pole transformer and using a SRSG. I did have an electrical engineering background though and thought that I could pull it off on the first attempt. That coil turned out great and worked the first time with 8 foot streamers from 4.8 KVA of power. I did a huge amount of research and used design software before I built anything. I also had the benefit of excellent tools and equipment. That being said, as has been suggested, it would probably be better to start with something simpler such as a static gap especially since you are using a NST.
I should tell you that building the SRSG was the most difficult part of the entire coil. There is no single source that will tell you how to build one. Search the "pupman.com" archives for information. "4hv.com" is another source. Do an image search on Google under "rotary spark gap". I looked at pictures of almost every RSG that I could find and did a lot of reading before doing anything. I incorporated the best ideas from other RSGs and incorporated a few of my own. Mine consists of a 1/2 HP motor with 10" diameter rotor made of G10 with 4 flying tungsten electrodes turning 3600 RPM. The synchronous motor is achieved by grinding 2 flat spots 180 degrees apart on the armature of a conventional induction motor. An oscilloscope and optical sensor is one way to measure and adjust the synchronism with the 60 Hz power line. It is critical that the rotor be balanced with very high precision or the whole thing could fly apart or shake your coil to pieces. I am stating all of this to let you know that building a SRSG is not a simple process. Done incorrectly, it can be very dangerous.
Steve White
Cedar Rapids, Iowa
----- Original Message -----
From: "doug" <doug11642@xxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Tuesday, September 18, 2018 7:02:24 AM
Subject: Re: [TCML] Rotary spark gap
Hi Gary, Thank you for your reply. I know I am inexperienced in this field,
and thank you for pointing this out. Perhaps,tho, someone could point me to
some information on the design and construction of RSG's so I could become
more experienced.
Thank you again, Doug J.
-----Original Message-----
From: Gary Lau
Sent: Monday, September 17, 2018 8:11 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Rotary spark gap
Hi Doug,
I would urge you to consider using a static gap until you are an
experienced coil builder. There are many pitfalls to successfully
designing a coil using a rotary gap that are not evident to beginners.
Advice is often given recommending that NST powered coils use only a sync
RSG. I don't think there is anything inherently wrong with using an async
RSG with an NST. The real danger is using a variable speed motor and
running at too low an RPM that the cap doesn't discharge every half cycle.
The voltage builds on successive cycles until either the cap or NST
insulation breaks down from over-voltage. A properly set safety gap would
protect against that, but the discipline to correctly set that is uncommon.
13,000 RPM? The speed for a sync RSG is only 1800 or 3600 RPM, so you'd
have to throttle that way down, and risk going too slow.
Regards, Gary Lau
MA, USA
On Mon, Sep 17, 2018 at 7:52 PM doug <doug11642@xxxxxxxxxxx> wrote:
> I am building a rather small TC for [Ross Reynolds] a physics prof. at
> GVSU here in Allendale Mi. I have a sewing machine motor that turns at 13K
> – plus, under no load and would like some design ideas for using it to
> build a rotary spark gap for the little {demo} coil please.
> To give you some idea on the coil/ NST = 7.5/30, MMC = 18K X 5.2 nf, top
> load = 1.5” X 6” toroid.
> Any help you give me will help to inspire some students {maybe}!
> This coil, by the way, is a gift to my friend Ross!
> Doug J.
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxxxxxxxxxx
> https://www.pupman.com/mailman/listinfo/tesla
>
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