Vinnie,
Avoid the Hysteresis type synchronous motors which always start in a different phase position. Instead look for salient pole synch motors, also some are called reaction synch motors which will also work properly for your application.Usually if a motor is a hysteresis type it will state that on the spec plate.Â
John  Â
-----Original Message-----
From: Gary Lau <glau1024@xxxxxxxxx>
To: Tesla Coil Mailing List <tcml@xxxxxxxxxxxxxxx>
Sent: Sat, Dec 11, 2021 5:41 pm
Subject: [TCML] Re: Seeking parts for synchronous rotary spark gap.
Hi Vinnie,
>> Iâ??ve seen tungsten carbide crisscross electrodes insulated by nylon...
Are you referring to tungsten welding rods (not tungsten carbide)? I think
you're talking about what was called "Propeller Gaps". I highly recommend
propeller gaps for their relative ease of construction and ability to
utilize small, low-HP motors. My propeller gap is documented here:
http://www.laushaus.com/tesla/sync_gap.htm and references Terry Blake's RSG
gap page: http://tb3.com/tesla/sparkgaps/index.html
But before starting construction of any sort, are you certain that your
motor is the type that always starts with the same mechanical phase
relationship relative to the mains waveform? I'm not familiar with bodine
motors. There is a name for the type that always starts with the same
phase but I no longer recall the word...
Also, this is not at all obvious but when converting a coil from a static
spark gap to a 120BPS synchronous rotary gap, the lower break rate makes it
CRITICAL that the primary capacitance be increased substantially. To have
the same power throughput with a lower break rate and the same
bang-voltage, you have to have an increased capacitance, and consequently
need to adjust other parameters (typically secondary inductance) to keep
pri/sec resonance matched. And having a properly set safety gap in
parallel with the RSG is more than just a very good idea. Just want to
make it clear that one can't just swap out a SRSG for a static gap without
a substantial coil redesign.
Regards, Gary Lau
MA, USA
On Sat, Dec 11, 2021 at 3:52 PM Tesla Burton <teslaburton@xxxxxxxxx> wrote:
>
> Hi all I have a small bodine synchronous motor and Iâ??ve been looking for a
> small rotor for it. Itâ??s a 1/4 shaft. Iâ??ve seen tungsten carbide crisscross
> electrodes insulated by nylon or some sort of non conductive plastic but I
> have no info on where or how to make such a rotor and point assembly.
> Alternative I could use a small disc type rotor but the ac motor has barely
> any hp or torque. Iâ??m somewhat of a novice but my current coil uses an RQSG
> and two 12k / 30ma neons in parallel.
>
> Thanks for your time
>
> VInnie