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Thread: Integral Unit (Chiller w/ VFD) Input Conductor Sizing

  1. #11
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    Quote Originally Posted by steve66 View Post
    Why is the VFD nameplate twice the motor nameplate? I can't believe they used a VFD twice as large as necessary on a motor that size.
    I wondered about that too. Not only that, it's VFD input current that's given. The rated output current is usually significantly higher than that. So more than twice the motor rating.
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    Quote Originally Posted by steve66 View Post
    Why is the VFD nameplate twice the motor nameplate? I can't believe they used a VFD twice as large as necessary on a motor that size.

    I assume everything is rated at 480 volts?

    IMO, its a packaged unit, and you should use the unit nameplate. The VFD nameplate would only apply if the VFD were installed as an individual piece of equipment.


    I would suspect it would because the manufacturer of the chiller only wants to stock a limited supply of sizes of VFD's. I would be under the impression that since it is a package unit then you design around the equipment's nameplate and not the VFD's nameplate as there is no way that they could upsize the motors on the chiller to get more capacity, which I believe is the reason why we design around the VFD's rated input when the motor and the VFD are separate items.

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    Quote Originally Posted by Besoeker View Post
    I wondered about that too. Not only that, it's VFD input current that's given. The rated output current is usually significantly higher than that. So more than twice the motor rating.
    Its almost like the VFD input voltage is 208V, and the output voltage (and motor voltage) are 480V.

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    Quote Originally Posted by Besoeker View Post
    I wondered about that too. Not only that, it's VFD input current that's given. The rated output current is usually significantly higher than that. So more than twice the motor rating.
    Its almost like the VFD input voltage is 208V, and the output voltage (and motor voltage) are 480V.

    Are there VFD's that can take either 208 or 480V as the input, and provide the correct 480V output for the motor?

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    Quote Originally Posted by steve66 View Post
    Its almost like the VFD input voltage is 208V, and the output voltage (and motor voltage) are 480V.

    Are there VFD's that can take either 208 or 480V as the input, and provide the correct 480V output for the motor?
    No, so far you cannot create voltage that is not there to start with without a transformer, at least not above about 1HP (using a voltage doubler circuit on the front end of the drive).

    The other way (480V input to a drive to run a 208V motor)? Yes, although its a really bad idea.

    Several of the Japanese mfrs, Mitsubishi for one, really only make a single drive that is a "400V class", which accepts anywhere from 380-480V input. But when they get them UL listed, they interpret the rules (or don't want to pay extra) to mean that it must be listed for a particular HP regardless of the voltage rating. So the drives end up looking over sized for our motors, which can cause issues with conductor sizing.

    But this is too much of a difference to be that issue. I agree with Knightryder12, it must be that the OEM wants to stock one VFD for any voltage, rated for the highest voltage, sized for the lowest. It only makes sense if you are intent on trading convenience for component cost.
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    Quote Originally Posted by Jraef View Post
    No, so far you cannot create voltage that is not there to start with without a transformer, at least not above about 1HP (using a voltage doubler circuit on the front end of the drive).
    Sorry to disagree, but yes you can.
    And we have.

    My basic equations for step up choppers:

    Name:  Stepupchopper01_zpsf57870f3.jpg
Views: 192
Size:  38.5 KB

    We have used these on VSDs up to several MW.

    Specials of course.
    Si hoc legere scis nimium eruditionis habes.

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    Quote Originally Posted by Besoeker View Post
    Specials of course.
    You mean the HVAC manufacturers are not queuing up to buy them?

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    Quote Originally Posted by GoldDigger View Post
    You mean the HVAC manufacturers are not queuing up to buy them?
    They'd want them for the price of a piece of toast.
    Si hoc legere scis nimium eruditionis habes.

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    Quote Originally Posted by Besoeker View Post
    Sorry to disagree, but yes you can.
    And we have.

    My basic equations for step up choppers:

    Name:  Stepupchopper01_zpsf57870f3.jpg
Views: 192
Size:  38.5 KB

    We have used these on VSDs up to several MW.

    Specials of course.
    Yes, but what you do is beyond the realm of what most people experienc day to day as electricians. And that is really difficult to find. I recently needed a boost converter for 30HP motors where the only available input was 240V single phase, but the only motors that could do the job were 480V servos (our VFDs can run servos). It was for an OEM who would buy about 100/year. I tried dozens of sources, no takers. I should have thought of contacting you...

    They ended up finding a third-tier servo company in China that would make them a 240V servo motor that big. If it ends up failing and they come back to me, I'll get hold of you...
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    chiller vfd mocp-mca

    we have done a number of water cooled chillers & the newer frictionless motor chillers with a vsd or vfd factory mounted controllers, they always put the chiller
    fla & mca tag on one end, and a different tag for the vfd on the vfd on the other end, it always seem like the vfd's are way larger than needed for the motor which
    they serve which leaves you in a problem with the circuit and breaker selection. the one thing we have found is even though the internal vfd disconnect-breaker
    have always been of the adjustable type with the breaker's setting, set or programed at the factory, if not then the chillers factory tech doing start up should catch this
    during his pre startup check list, & then reset & reseal the breaker to the proper settings as per code.. we always seem to end up fighting the the consulting engineer & owner over this.:

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