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???
08/27/09 13:15
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 		 #168566 - with these questions
Responding to: ???'s previous message
What I need to know is:
1.What should be the frequency of the PWM signal?
2. If I have to reduce the speed, then do I have to change the frequency of firing so that the supply to the motor is 3phase @25Hz, but the PWM frequency remains the same.

I suggest you buy an inverter (you do not state amps, but from the components I guess not a lot) which, for the size I guess, should be available for about $200.

Attempting a repair of the old unit will, most likely, cost you more and if you are not successful in repairing the old unit and connect it you may have the added expense of a motor.

should you insist then 1) the frequency the motor is rated at (maybe +20%) 2) yes but how can you have half frequency and "the PWM frequency remains the same". The reson I state "(maybe +20%)" is that not many motors run good at half speed and making full speed a bit higher makes hal;f speed higher too. Also, you need to control the voltage for half speed.

Any error will BURN THE MOTOR (seen it happen)

Erik

List of 29 messages in thread
TopicAuthorDate
AC Motor question            01/01/70 00:00      
   with these questions            01/01/70 00:00      
   More questions            01/01/70 00:00      
      not neccessarily            01/01/70 00:00      
         May be, but...            01/01/70 00:00      
            inverters have a potentiometer input            01/01/70 00:00      
   Replies to Erik and Daniel            01/01/70 00:00      
      go ahead and then cost it            01/01/70 00:00      
         Thanks Erik            01/01/70 00:00      
   Dear Suttar            01/01/70 00:00      
      STAY AWAY            01/01/70 00:00      
         It doesn't have to be so bad if you switch at zero crossing            01/01/70 00:00      
            and give tyhe AC motor every other cycle ????            01/01/70 00:00      
               No ... just turn it on and off at zero crossing            01/01/70 00:00      
                  it is an AC motor, details, details, detalis            01/01/70 00:00      
                     Horrible motor control            01/01/70 00:00      
                     Who said anything about removing cycles?            01/01/70 00:00      
                        on and off at zero crossing....            01/01/70 00:00      
                           and if you cut only half cycles ....            01/01/70 00:00      
                              Nope ... it just happens at power-on and power-off            01/01/70 00:00      
                                 that is NOT what this thread is about            01/01/70 00:00      
                           Only when you turn the motor on or off            01/01/70 00:00      
         To Erik,            01/01/70 00:00      
            Slip            01/01/70 00:00      
               "inverter certified" motors ...            01/01/70 00:00      
            Creating new sine wave at different frequency            01/01/70 00:00      
               Now I know why...            01/01/70 00:00      
            no, the frequency generated by the inverter            01/01/70 00:00      
      Reply to Vu Nhu Khanh            01/01/70 00:00      

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