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Thread: Fla

  1. #1
    Join Date
    Aug 2003
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    59

    Hmm Fla

    Another elementary question, but certainly leads to debate.
    During a pm of equipment, I was told by some that motor amperage should be as close , or adjusted to (if possible) to Full Load Amps. In this way, the motor is running as efficiantly as possible. Or in other words "optimized"
    Others , however, say that that is not true and I should back off the amperage draw by adjusting the sheive, that FLA is the MAXIMUM acceptable amount of amperage draw for the motor and I will be shortening the life expectancy of the motor if I keep it at that range. I have been adjusting the sheive to about 80% of FLA to stay in the safe area. Am I wrong?
    Should I be trying to "optimize" the motor and bring it to FLA?
    Thanks...

  2. #2
    Join Date
    Apr 2007
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    6,285
    You need to go by your operating conditions (meaning evap. temps and condensing temps) that are called for by your compressor manufacturer. Copeland has the performance calculator Bristol has the efficiency sheets. I'm sure almost every manufacturer has info like this about their compressors. RLA is what the amperage draw is at test conditions if you are below these your draw will be less.

  3. #3
    Join Date
    Aug 2006
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    Mixing oil and fire with a big spoon.
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    are you speaking of air flow?

    if so, the sheave size should be adjusted to supply the proper amount of air flow only. we do not have an infinite number of motors with every horsepower ever needed. therefore, you need to use a motor that will allow you to reach your required air flow. if that means you need 0.9 HP then you will need a 1.0 HP motor. if you need 1.1 HP then you will need a 1.5 HP motor. you may be able to get away on the 1.1 HP requirement with a 1.0 HP motor if you had at least 1.10 SF (service factor). while running a 1.0 HP motor on a 1.1 HP requirement does give you more electrical effeciency...you also have no safety room at start up or brown out conditions or temporary overloads or lots of cycling. the FLA rating (Full Load Amperage), is a number indicating the amps expected at that HP and voltage and hertz listed on the nameplate. you may or may not have these conditions...esp. voltage.

    so stop adjusting sheaves because of amp draw. i would only adjust them if my motor were tripping due to some unknown cause and i needed it to run in order to troubleshoot. the only other reason to adjust them is because the balance report said so or conditions changed that required more or less air flow.

    good luck.
    my 1st time jumping out of a plane...http://youtu.be/Kv38G0MHsGo

  4. #4
    Join Date
    Aug 2006
    Location
    st.petersburg,fl
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    Lightbulb

    Be careful on what you start adjusting during pm s

    Talking about Test and Balance

    Depending on what you're adjusting you may be throwing off the balance of the store or resturant ...ie. exhaust, maf, blowers.
    and cause more trouble than you are looking for...
    Isn't sanity just a one-trick pony anyway? I mean, all you get is that one trick, rational thinking, but when you're good and crazy, well, the sky's the limit!

  5. #5
    Join Date
    Jan 2004
    Posts
    1,174
    OOPS, so much for that expensive air balance, FLA is a max, there is no minimum, kick the guy in the ass that told you to that.

  6. #6
    Join Date
    Oct 2006
    Location
    Central Texas
    Posts
    625
    Quote Originally Posted by mickyj View Post
    Another elementary question, but certainly leads to debate.
    During a pm of equipment, I was told by some that motor amperage should be as close , or adjusted to (if possible) to Full Load Amps. In this way, the motor is running as efficiantly as possible. Or in other words "optimized"
    Others , however, say that that is not true and I should back off the amperage draw by adjusting the sheive, that FLA is the MAXIMUM acceptable amount of amperage draw for the motor and I will be shortening the life expectancy of the motor if I keep it at that range. I have been adjusting the sheive to about 80% of FLA to stay in the safe area. Am I wrong?
    Should I be trying to "optimize" the motor and bring it to FLA?
    Thanks...
    Yes, your actual amp draw should be close to rated load amps RLA (FLA). Electric motors have a service factor (SF on name plate) usually 1.15. This means you can take the SF X the RLA and look at your actual amps this will be the maximum amp draw. I am assuming that this is an indoor fan on a RTU or air handler. Hope this helps
    Sic Semper Tyrannis.

  7. #7
    Join Date
    Feb 2004
    Posts
    43
    stay away from adjusting for rla, when design conditions are meet, like a properly charge compressor circuit your not looking always at fla to be meet, this is asking for trouble.... and usally 3 phase gets a sf, you better look for a name plate data if there is a sf to play into.. not all motors have a sf..go for what is needed only. i know your asking about air handler but think about it first,, don't cause more problems.

  8. #8
    Join Date
    Dec 2006
    Location
    toronto, canada
    Posts
    551
    i think all the RLA, FLA, LRA on the name plate are got in labs or ideal condition. so what we get on field always have some difference from it. we cant judge the system only by the amps.

  9. #9
    Join Date
    Jun 2004
    Location
    St Paul, minnesota
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    keep in mind readings should be taken with a true rms amprobe or else you will have additional problems

  10. #10
    Join Date
    Jul 2000
    Location
    Dallas,Texas
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    4,948
    Quote Originally Posted by superfittertech View Post
    keep in mind readings should be taken with a true rms amprobe or else you will have additional problems
    Can you qualify that statement?

    An averaging meter is all many service people will ever need. Unless the load has non-linear elements in it such as a VFD or neutral harmonics, the true rms and averaging meter will read the same.



    http://us.fluke.com/usen/Home/Search...x=rms&x=7&y=1#

    "Why True -RMS?"

    "Why Tru-RMS matters for HVAC technicians?"

  11. #11
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    Dec 2001
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    Southern Tier, NY
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    good post, Wolfie.....

  12. #12
    Join Date
    Aug 2006
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    Mixing oil and fire with a big spoon.
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    [QUOTE=wolfdog;1526591]Can you qualify that statement?

    An averaging meter is all many service people will ever need. Unless the load has non-linear elements in it such as a VFD or neutral harmonics[QUOTE]

    exactly...ever have a bad drive "echo" throughout the building? i have heard of one building without drives have lots of problems because of the building next door. if you are in commercial...just get a true rms meter. most do not cost much more.
    my 1st time jumping out of a plane...http://youtu.be/Kv38G0MHsGo

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