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  1. #1
    Join Date
    Jun 2019
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    Nameplate 5 ton LRA 20A -- can this be real -- sizing a generator

    I'm looking at residential standby generators that would power my 5 ton HVAC. It's a newish model very high SEER, digital controlled scroll compressor.

    My generator vendor has calculated sizing using a six fold multiple of RLA. Reading other threads this is a pretty typical assumption for inrush current LRA calculation.

    But...
    The nameplate on my outside unit states RLA 20 AMPS / LRA 20 AMPS. Is this LRA value usable for sizing a generator? Obviously a big difference between 20 AMPS and 6 X 20 AMPS.

  2. #2
    Join Date
    Mar 2018
    Location
    Chico, Ca #StateofJefferson
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    This is an inverter system I take it? If so, I would thing that its accurate but you need to factor in the amp draw of the airhandler, any supplemental heat strips, etc as well. I dont size generators so take it for what this is worth, but inverter compressors really dont have any inrush as they use a soft start on the compressor where it ramps up to its requested speed over the course of a minute vs going from 0-100 in a quarter second

  3. #3
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    Jun 2019
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    Thread Starter
    Thanks makitcold it is an inverter system. I trusted the nameplate info but I'm surprised not to have seen this benefit of digital controlled inverters mentioned around the web on generator sites. It can have a BIG impact on generator sizing.

  4. #4
    Join Date
    Aug 2002
    Location
    Southold, NY
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    Quote Originally Posted by MikeBW View Post
    Thanks makitcold it is an inverter system. I trusted the nameplate info but I'm surprised not to have seen this benefit of digital controlled inverters mentioned around the web on generator sites. It can have a BIG impact on generator sizing.
    Be more concerned with the Gen putting out a clean sign wave AKA Clean power.

    Computers don’t like dirty power!

  5. #5
    Join Date
    Dec 2007
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    Quote Originally Posted by pecmsg View Post
    Be more concerned with the Gen putting out a clean sign wave AKA Clean power.

    Computers don’t like dirty power!
    EXACTLY!!!!!!

    I have seen many motors and controls rendered useless on generators that either were never set up properly, undersized and/or delivered dirty power.

    Personally, if this is straight a/c, I would not use it on a generator. Live through the time on the generator without a/c. Now if the indoor equipment is computer controlled, ECM blower motor and/or inducer motor, you need to make darn sure you get something from the installer in writing that it won't be an issue.
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  6. #6
    Join Date
    Nov 2004
    Location
    SW FL
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    Quote Originally Posted by pacnw View Post
    EXACTLY!!!!!!

    I have seen many motors and controls rendered useless on generators that either were never set up properly,
    undersized and/or delivered dirty power.

    Personally, if this is straight a/c, I would not use it on a generator.

    Live through the time on the generator without A/C.

    Now if the indoor equipment is computer controlled, ECM blower motor and/or inducer motor,
    you need to make darn sure you get something from the installer in writing that it won't be an issue.
    ____ ABSURD IN FLORIDA.
    ___ NO POWER FOR A WEEK OR TWO
    … … … PEOPLE DIE

    + VIOLATION OF RECENTLY ENACTED FL STATE LAW for ANY Assisted Living Facilities (ALF)
    ________________________________________
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  7. #7
    Join Date
    Jun 2003
    Location
    Texas
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    1,494
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    inverter generator? don't know anything about gens. but my honda 3000ie I think it is does the same work a 5k work horse would do and is a hell of a lot quieter. don't use it on the house though.

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