[TCML] Variable RSG
jimlux at earthlink.net
Wed Apr 9 21:22:16 MDT 2008
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?
>> 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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