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Re: [TCML] Variable RSG

FutureT@xxxxxxx wrote:
In a message dated 4/9/2008 6:51:35 P.M. US Eastern Standard Time, quarkster@xxxxxxx writes:
Let's also make sure that everyone is talking about the same type of motor.
When we're talking about a >motor for use with a Synchronous Rotary Spark Gap, and "synchronizing" the rotor angular position >with the sine wave of the AC power supply, we are usually talking about a "salient pole" type motor,
either factory-made (like used in a Teletype machine) or a modified (flats 
machined on rotor) >synchronous induction  motor.
Miles' original post dealt with adjusting the phase of a "syncronous" 
motor, and there was no mention >of  salient-pole modification.
I've experimented with John Freau's phase adjust circuit using 
salient-pole motors, and it works  as >advertised.
However, I've never tried it on an un-modified synchronous motor
(conventional squirrel-cage induction >motor). Does it work on an regular squirrel-cage motor? 


 Regards,
 Scott Hanson



Scott, all,
A conventional squirrel-cage induction motor is not a synchronous motor. Such a motor will always slip and run slower than the synch speed.
Ah.. but the advent of the Variable Frequency Drive makes it possible (albeit not trivial) to actually get synchronous behavior from the motor/controller system. Essentially the controller commands a frequency that is enough higher than the desired rotation frequency to get the output to actually be at the desired speed (i.e. drive the motor at 65 Hz to get 1800 RPM or whatever).
I don't know if the inexpensive drives have a tach input and/or the phasing/sync input, but more expensive drives do. If you're doing something like a rolling mill or a web printing press, where you've got lots of motors that all have to operate as if they were "geared" then this capability is quite handy. Exceedingly tough to get to work if the load is changing, but a RSG is a pretty stable load. 

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