Re: SRSG questions

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: FutureT@xxxxxxx 

In a message dated 3/27/06 4:58:59 PM Eastern Standard Time, 
tesla@xxxxxxxxxx writes:


> I'm trying to build a SRSG for my next coil and I've got a few
> questions. I've found from others examples that I need an 1800 or
> 3600 RPM synchronous motor. I called our local motor store and they
> assured me they had a 1/3 hp 1800 RPM synchronous motor. I went to go
> buy this motor and found that the stamp on the casing says 1725
> RPM's. The sales person said it was a synchronous motor built with an
> outer coil with spinning bars on the inside as opposed to the 2 coil
> system, so it appears he knows what he's talking about. My question
> is could I use this motor for a SRSG? My next question is what is G10
> and where can I get it? Apparently everyone uses it for their disc
> but I've never even heard of it. Finally, I noticed the recent post
> on power arcing of SRSG's but I don't know what power arcing is.
> Could someone explain please? As always I appreciate the help.


It's hard to imagine that the motor is truly 1800 rpm synchronous
if it has 1725 rpm stamped on the case.  To be sure you'd need
to attach a cardboard disc onto the shaft and power up the motor
under ballast-type fluorescent light.  A white or black line should be drawn
across the disc.  If the motor is running in sync, you'll see a
stationary pattern on the disc.  However many folks cannot see
this pattern without a lot of training or experience.  By using
a true stobe light timed to the incoming AC the task is made
easier.  If the motor is an ordinary 1725 rpm induction motor
then it is possible to modify the motor by grinding 4 flats on
the armature to make it truly synchronous.  Many folks on this
list have done this with excellent results.

G10 is an epoxy and fiberglas type composite material
similar to phenolic but stronger.  McMaster Carr sells it.
It's somewhat tough to machine.

Power arcing with SRSG's is usually not an issue except at
very high powers or higher break-rates with slow rotary speeds.
Power arcing occurs
when the gap electrodes run hot and cannot quench properly.
It also tends to occur if the transformer is not ballasted
enough.  NST's of course are internally ballasted so they
don't need extra ballasting.  The ballast limits the input
current and tends to prevent power arcing.  There are a
number of other factors that promote power arcing such
as using too-thin electrodes which will run too hot, using
very low rotary speeds with async rotaries, etc.

Be sure your motor has no end play so you can set the
electrode spacing rather close without danger of them
crashing.  The required electrode spacing depends on
the voltage and power level of the system.  A too wide
spacing will cause erratic and inefficient operation.
Usually the spacing should be 0.020" or less except
maybe on high powered systems.

I show a few SRSG's at my website.  The photos are
distributed on various pages at the site.

   http://hometown.aol.com/futuret/page3.html

I also have spun aluminum toroids available which
can be seen at my website.  There's also a section on
Tesla coil efficiency and other things.

John