Sync RSG

Salient-Pole Synchronous

Rotary Spark Gap

This is the original rotary gap I made fro my 6" coil and it's still in operation.

(Click on images to see a larger version)

This is the setup I used to modify the 1725 rpm motor for 1800 rpm salient-pole operation. Constructing the mounting fixtures (tale-stock, bushings, etc.) took many many hours while the actual cutting was quick and easy. The modification was done per the directions posted on Brent Turners ftp site or you can download them from here (download motormods.zip).

Motor operation was exactly as expected with one problem in the test setup (If you are using a florescent light as a strobe insure it's not an electronic ballast type since they don't operate at mains frequency).

Here is the initial setup (note: the electrodes and holders were eventually redesigned). The motor and rotor run very smooth with almost no vibration.

Initial HV testing exposed a design flaw. The spacing between the conductive (and grounded) mounting screws and the electrode holders was not enough to prevent HV creepage and ultimate arcing across the phenolic. Additionally, the sharp square edges of the electrode holders cause voltage stresses at exactly the wrong place. I reworked the mounting system to increase clearances and round off the sharp edges but continued to experience numerous problems and erratic operation.

I got so frustrated at this point that I almost scrapped the whole thing.

Cooler heads eventually prevailed and I put it aside for 6-months. After a break I attacked with a new determination.

The redesigned unit functioned GREAT!

That is, until the cloth skirt around the base of my coil blew into it while it was spining fuull speed! Sorta like the feces hitting the rotary oscillator (See all the broken flying electrodes)...

021100e.jpg (24662 bytes)

I replaced the electrodes and my coil now produces 6' to 7' arcs and sounds like it will come and get you (there is no other sound like a synchronous coil). It also runs for as long as I want without any degradation in the consistent performance.

There is no indication of overheating on the flying electrodes even during 2+ minute runs at 3kw. I'm very pleased with its operation now that the bugs are worked out.

Specifications of the redesigned unit

Motor	3/4hp, 1725rpm, CS/IR, Ball-bearing motor. Modified for 1800rpm salient pole synchronous operation.
Rotor	LE Phenolic disk 1/2" thick and 9" in diameter. The eight electrode holes are evenly spaced at a radius of 3.75"
Flying Electrodes	Eight 1/8" Thorated-Tungsten rods pressed into 1/2" brass holders.
Fixed Electrode	Four 1/2" steel rod tipped with 3/8" Tungsten electrodes.
Fixed Electrode Holders	Aluminum blocks mounted onto round plastic insulators (adjustable in three axis').
Crossbar	Aluminum electrode holder mounted on plastic insulators with a low resistance copper interconnect.
Configuration	Four series gaps configured to give 240 breaks-per-second.
Mechanical Dwell	.7 ms
Electrode Velocity	59fps

Here are a few shots of the SRSG in it's final form.