480V single phase into a VFD

Discussion in 'General Electronics Chat' started by strantor, Aug 11, 2011.

  1. strantor

    Thread Starter AAC Fanatic!

    Oct 3, 2010
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    There have been a few questions about running 3 phase motors on single phase lately which has sparked my own curiosity. Suppose you have a 480V 3phase motor and a 480V 3phase Variable Frequency drive, but your only power source is 120V single phase. Could you use a transformer to step up the 120V to 480V and feed 480V single phase to the VFD? I know most VFDs have incoming phase loss detection and will likely fault out, but supposing you had a way to disable this fault, I don't see any reason why it wouldn't work in theory. Has anyone here tried it?
     
  2. gerty

    AAC Fanatic!

    Aug 30, 2007
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    In a word...yes. It'll work, but by the time you bought a step up transformer you could've wired the place for220. We have a pump trainer here at the school, it's portable, so it has a 120v cord on it, plug it in anywhere. It has a single phase in-3 phase out VFD on it to power a 208v 3 phase motor. In my motor control stuff we use a similliar converter.
    Another issue would be the current, to get 10 amps of 480v, you'll need 40 amps of 120v.
     
  3. tom66

    Senior Member

    May 9, 2009
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    Also with three phase a filter capacitor is not always necessary as it never drops to zero. Single phase does. This may cause trouble.
     
  4. strantor

    Thread Starter AAC Fanatic!

    Oct 3, 2010
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    Yeah transformers aren't cheap. I did find this: http://cgi.ebay.com/25kva-transform...uit_Breakers_Transformers&hash=item41583a6d0c

    If you already had the drive and the motor (which coincidentally I do) then 300$ for the transformer might still be economical.

    As far as the caps; the caps in a drive hold an awful lot charge. The ones I have worked with have an option for "power loss ride-thru" where it will continue to power the load for a few seconds if you disconnect the mains.
     
  5. gerty

    AAC Fanatic!

    Aug 30, 2007
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    What size motor do you plan on running? If you have enough 120v current available you shouldn't have a problem.
     
  6. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    I've commissioned 1000+hp motors on a 60amp service. How?, speed with no torque, or torque with no speed. Add the two together and there goes your fusing. What's the point?, consider how your VFD's input section will handle the power requirements. If those requirements are with in the individual phase components, you'll not have a problem (faults jumped). That would likely imply oversizing the drive. Consider that on top of the oversizing the 120 sourcing element (stepdown) to get the afore mentioned current, and it doesn't make a lot of sense.
     
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