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    New vs Older vfd

    Just a heads up.

    Customer called to complain his replacement VFD was tripping the Pushmatic breaker. We had put in a larger breaker when the previous drive was first installed. Well, turns out the previous drive only had to be sized about twice up for single phase input. New one requires four times up. This drive input is rated at 68 amps three phase. We only have a 70 amp single phase service to the building. It is what it is for the moment.

    Tech support says new models have smaller capacitors so they have to be upsized 3-4 times vs the 2 it used to be.
    Tom
    TBLO

    #2
    Originally posted by ptonsparky View Post
    Just a heads up.

    Customer called to complain his replacement VFD was tripping the Pushmatic breaker. We had put in a larger breaker when the previous drive was first installed. Well, turns out the previous drive only had to be sized about twice up for single phase input. New one requires four times up. This drive input is rated at 68 amps three phase. We only have a 70 amp single phase service to the building. It is what it is for the moment.

    Tech support says new models have smaller capacitors so they have to be upsized 3-4 times vs the 2 it used to be.
    Well, it's not actually "smaller" caps in terms of capacity, it's that they are made to get more capacitance in a smaller can in order to make a smaller drive package, but that means they will over heat more easily when being used on high ripple applications such as converting single phase. 4x is pretty extreme from my experience, but I've seen it listed as a 65% de-rate, meaning using at 35% of rated when feeding with single phase (assuming a drive that is not designed for single phase input), so that's pretty close to 3x over sizing. If you use a VFD that has a built-in DC bus choke, you can go back to a 50% de-rate. But that usually only comes on the high-end drives.
    __________________________________________________ ____________________________
    Many people are shocked when they discover I am not a good electrician...

    I'm in California, ergo I am still stuck on the 2014 NEC... We'll get around to the 2017 code in around 2021.

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      #3
      Tech support indicated they have a supplement to the manual that would give the 1ph current. IIRC it was about 45 amps to feed the 5hp submersible. 1.25*45 is a lot more realistic than the 1.25*68 the NEC requires.
      Tom
      TBLO

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        #4
        That’s what I have seen with vfd’s on 5 hp 3 phase submersible motors.

        A franklin or Pentair drive designed for single phase in and three phase out, will only require a 50 or 60 amp breaker.

        However a Yaskawa being used as single phase in and three phase out will require an 80 amp breaker. This is because of having to oversize the VFD as you mentioned.

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          #5
          Yeah, because most Asian drives don’t have DC bus chokes. Capacitors are cheap for Asian drive mfrs since most caps are made by the same companies. Big chunks of steel wrapped with copper wire (aka chokes) are expensive to ship from Asia.
          __________________________________________________ ____________________________
          Many people are shocked when they discover I am not a good electrician...

          I'm in California, ergo I am still stuck on the 2014 NEC... We'll get around to the 2017 code in around 2021.

          Comment


            #6
            The latest crop of Schneider (TMEIC) drives have DC bus chokes available and the pricing is comparable to the low cost brands. Might look at the price of a 312 or 630 series.

            Sent from my SM-T350 using Tapatalk

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