Re: [TCML] SRSG Motor Problem

[futuret@xxxxxxx]

 Andrew,

For Tesla coil work, a sync motor is usually an AC motor which runs in sync with
the AC line frequency.  The most common speeds for Tesla work are 1800 rpm, and
3600 rpm, in the USA and other countries using 60Hz power.  Yes, a sync motor
runs at a multiple of the AC line frequency.   

Although a hysteresis motor is a sync motor, it will start up each time at a different
phase setting.  This makes it rather "bad" for TC use because the phase has to be
re-adjusted every time the coil is run.  For TC work it's best to use a sync motor
which locks into phase at the same position or setting every time it starts and locks.

Examples of these "good" types of motors are; modified induction motors, salient pole sync
motors, and reaction sync motors.  These are terms that are often used to describe
these types of sync motors which lock in speed and phase to the incoming line frequency.
Yes, these "good" motors lock to a specific phase position or setting each time they are started.
So once the initial phase is set, either mechanically or with an electronic phase shifter
circuit, then they'll remain set properly for a given Tesla coil and power level.  

Sync motors don't tend to fluctuate much in speed or phase while they're running. 
They tend to be stable.  It's not something to worry about.  

If you modify an induction motor, a 1725 rpm motor will become an 1800 rpm sync
motor, and a 3450 rpm motor will become an 1800 rpm motor.  

You cannot buy an 1800 rpm or 3600 rpm induction motor.  By definition an ordinary induction
motor is not synchronous unless you modify it by grinding flats on it to make it
synchronous.  Induction motors run at speeds such as 1725 rpm or 3450 rpm.
You can however buy an 1800 rpm or 3600 rpm synchronous motor (but avoid the 
hysteresis types).  

Sync motors with low speeds such as 600 rpm or 900 rpm tend to be "bad" for
TC work because the spark gap dwell time tends to be rather long.  That can
often cause "re-firing" of the spark gap.  This causes great inefficiency and other
problems.  

John



 


 

 

-----Original Message-----
From: Andrew Robinson <teslamad@xxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Thu, Jan 28, 2010 4:35 pm
Subject: [TCML] SRSG Motor Problem


So we've run into a disastrous situation with our new SRSG. The motor is failing on us which isnt too bad since it was a hysteresis motor and only 600 rpm which scared us from the beginning. So heres the question for you guys. What defines a "sync" motor. Is it a induction motor that is designed to rotate at an rpm rating in multiples of the supply frequency... A 600, 1200, or 1800 rpm motor etc? Is it a motor that full fills the previous requirement but also doesn't fluctuate much in RPM, aka has a high RPM tolerance, maybe only changing by plus/minus half an RPM? Or do sync motors have some other property unknown to me... possibly having a way to "lock" phase. How it would do this i have no idea? 
 
I know people make sync motors out of induction motors by grinding flats in the rotor. By doing so are they trying to achieve a supply hertz rpm multiple? Can I go buy a 1200, or 1800 induction motor and use that, or are all 1200, 1800, etc motors considered "sync because of their rpm rating (supply hertz multiple)? 
 
Visit http://www.teslamad.com/ to see the sync gap im talking about. If anyone has a sync motor thats about the same size (115v 60Hz single phase, about 4" in dia, .5" axle dia)   that you'd be willing to sell, donate, or maybe trade, please let me know. See the 4 SALE link at the bottom for things I can trade off or would be willing to sell too. Thanks everyone. 
 
Regards, Andrew Robinson 
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