Re: [TCML] July 4th and why not to be in a hurry

[FIFTYGUY@xxxxxxx]

In a message dated 7/9/08 12:24:11 A.M. Eastern Daylight Time,  
pslawinski@xxxxxxxxx writes:

>The  variable frequency drive is a nice touch.  How do you vary the speed  
while the coil is running?


Well, I can tell you how *I* do it - I  turn the knob on a 10k potentiometer. 
:)
 
    Actually, I decided to go with a VFD-controlled  ARSG after Bart 
described his setup. I use an old junk Motortronics drive, and a  1/2 HP 3600rpm 
motor. I use XLR connectors at the motor and the control cabinet,  with a shielded 
cable to connect. 
    I already had a 3/4 HP single-phase motor that I  had modded for SRSG 
use, but I never even gave it a try. Went right with the  VFD. I think it's a 
very slick setup - a VFD has many advantages:
 
    -instant readout of motor current, rpm, or even BPS  if you configure it 
that way
    -motor overcurrent, overheating, stall, phase  loss, and ground fault 
protection built in and instantly  adjustable
    -frequency avoidance to prevent damaging vibration  modes
    -braking by dynamic (or regenerative if you spend  the money!) easily 
implemented, especially in case of fault
    -gradual acceleration/decel to avoid stress. I use  20 seconds of accel 
time, with 10% S-curve. Makes for a very smooth start with  nice slow speed 
changes, in case something is loose or out of adjustment
 
    Small (fractional-HP) 240V VFD's are a dime a dozen  these days, so no 
big loss if you smoke one.
 
-Phil LaBudde

Center for the Advanced Study of Ballistic  Improbabilities



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