[TCML] Variable RSG

[Jim Lux]

FutureT at aol.com wrote:
>  
> In a message dated 4/9/2008 6:51:35 P.M. US Eastern Standard Time,  
> quarkster at att.net 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.