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3phase induction motors

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jennifer:
    Im looking @ getting a new fan for the booth...I would like to control the speed of this fan, If a 3/4hp motor is run on a 110 line
using a VFD,
     #1 Is it possible using the 110/60hz?
     #2 Would a starter have to be included in this design?
     #3 Can a Vfd be set to start again @ 60hz on start up (every time its turned on)?
     #4 Is there a better way?
     #5 Is controlling a single phase with a rheostat any safer?

MonMotha:
3 phase motors do not require start/run capacitors as you may know.  The VFD should be able to implement soft-start for the motor, and it'll do so in a way much nicer than pretty much any other solution.  As to whether it can be set to remember speed upon power on, that'll depend on the VFD but it should be a common feature.  Many of them have programmable startup patterns.

Do you actually have 3 phase service?  If not, you'll need to find a VFD that's single phase in / 3 phase out.  That's electrically quite doable, and I'm guessing they do exist.  Most three phase motors are 208/240 delta, though.  120V would only be for wye, which I don't see on motors very often.  To run a 208/240 motor off a 120 single phase circuit, you also need voltage boost.  Again, electrically quite doable, especially at only 3/4HP, but it will limit your choice of VFD.

At 3/4HP, you can probably get by with a conventional chopper style speed controller like are used to control power tool speeds and a universal (brushed) motor.  Not the nicest thing for the motor, but it'll work.  Won't work with an induction machine, though.

jennifer:
       Quite informative, void or RPM formulas and written so as even a girl can understand.... Thank you for that.
 No I dont have 3phse service, but after looking into what you said a inverter style 120v to 220v VFD (apparently there is such a thing)
 Is what I need. Horsepower ratings seem to be a thing, So in typical Jennifer overbuilding fashion the 2hp is overkill But should allow
 for more headroom (bulletproof). Im feeling much better about this project, and no longer scared of it. :applaud:

Ed_McCarron:

--- Quote from: jennifer on November 17, 2012, 04:15:18 pm --- a inverter style 120v to 220v VFD (apparently there is such a thing)

--- End quote ---

There is such a thing -- I just set up two for a customer, driving chemical feed pumps.  They were spendy.  I'll see if I can get part #'s for you.

lilshawn:
http://www.bardac.com/pages/products/ac_optidrive-i55.html

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