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Thread: out of ideas

  1. #1
    Join Date
    Dec 2009
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    Buffalo, N.Y
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    101

    Confused out of ideas

    I have a 2 hp squirrel cage blower kicking my ass. after about 200 hours run time max, motor #1 failed, overload stopped resetting. motor was drawing @ 10 amps, nameplate 11. Motor #2, drawing just under 11 amps, same sheave, same motor. #2 started cycling on overload after two weeks. when I was called, it was drawing 12.6 amps, cycling on OL, windings were chocolate color, checked capacitors, bought smaller sheave, motor draws 12.6 amps even unloaded. Replaced run cap., 12.6 amps. 4.15" sheave or 3.25" full open, 12.6 amps. WTF. Ok, motor is toast, got a new one,put it in.
    New motor runs the same, 12.6 amps. Motors all the same- 208/230 single phase. Line voltage is 246.5 with unit off, 244.9 running. Block the return air with cardboard- 12.6 amps. run without belt, 12.6 A. 4.15" sheave, motor loaded as much as I can, 12.6 amps. 3.25" sheave, 12.6 A

    UGGGHHHH.

    Customer has a newbuild 15,000 square foot home with all low voltage lighting. I start trying to shed power to the lights to see if anything changes. My thought was that all those electronics may be somehow altering frequency or changing the incoming power . No help, 12.6 A. This is one of my two residential accounts but all the equipment is commercial. I started questioning the 246.5 applied voltage, but it is within 10% of nameplate. measured 60 hertz, with lighting energized and off.

    I am out of options. right now my plan is to take both motors (#2 and #3) to be bench tested at a local electric repair shop.

    Any ideas or suggestions would be appreciated. If you made it this far into my long post, thanks.
    Dave.

  2. #2
    Join Date
    Jan 2008
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    Dallas ,Texas
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    What kind of equipment is it? If it's a air handler how much air is it moving? Is it TEFC ? I'll think of more later.
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  3. #3
    Join Date
    Dec 2009
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    Buffalo, N.Y
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    Quote Originally Posted by thegoodlistener View Post
    What kind of equipment is it? If it's a air handler how much air is it moving? Is it TEFC ? I'll think of more later.
    Its a geo-thermal pool unit with de-hum, re-heat, waste heat recovery, the whole nine. I have not measured airflow. The arrogant engineer designed this system at 3200 cfm (8 ton) and claims to have done such a perfect job that no balancing dampers are necessary. I did not install the ductwork, nor did my company have anything to do with it. I simply set up the blower by amp draw.I am trying to Isolate just this component to simplify things.

    TEFC? I'm drawing a blank on that one.

    Other details I forgot to mention, I am able to run only the blower, through its contactor and nothing else but wires, all thoroughly checked for any defect.

  4. #4
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
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    3,668
    Totally
    enclosed
    fan
    cooled motor
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  5. #5
    Join Date
    Dec 2009
    Location
    Buffalo, N.Y
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    Quote Originally Posted by thegoodlistener View Post
    Totally
    enclosed
    fan
    cooled motor
    No, open.

  6. #6
    Join Date
    Sep 2008
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    Western PA
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    24,998
    Well, since it is a squirrel cage, we rule out an air restriction which would actually reduce amperage.

    Honestly, since you say that the new motor was over amping, too, I have to vote for a mis-match. Call the manufacturer and verify that all components are correct for the application.

  7. #7
    Join Date
    Dec 2009
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    Buffalo, N.Y
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    Quote Originally Posted by jpsmith1cm View Post
    Well, since it is a squirrel cage, we rule out an air restriction which would actually reduce amperage.

    Honestly, since you say that the new motor was over amping, too, I have to vote for a mis-match. Call the manufacturer and verify that all components are correct for the application.
    manufacturer has supplied all motors. I toyed with the idea that 2 hp wasn't enough, but I can't even spin the blower, without moving air, at less than 12.6 A. Even without the belt, a motor is a motor, regardless of size, I would expect 5/8 to 3/4 fla.

    thanks for the replies.

  8. #8
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  9. #9
    Join Date
    Dec 2009
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    Quote Originally Posted by jpsmith1cm View Post
    So, the motor is drawing over FLA without a belt on it?
    yup- 11 A FLA, 12.6 A measured, two different motors, two different meters.

  10. #10
    Join Date
    Jul 2009
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    Is the home supplied with 3 phase and your taping a single phase off of that?
    Current Harmonics, and phase imbalance can occur on single phase equipment if i'm not mistaken. Are the start windings not DE energizing after motor spins up?


    Reliable, long-term operation of most electrical equipment requires a voltage imbalance of less than two percent; which means your system has too much imbalance.

    If you find voltage imbalances in your facility, the first place to look is not the power company. Instead, look for electrical distribution systems in which one leg of a 3-phase supply powers both single-phase and 3-phase loads. You may find single phase loads not evenly balanced across the phases. Or, look for in-line reactors installed to correct imbalances. These reactors usually have taps for adjustment, and somebody may have adjusted them. Or, the imbalance they originally corrected may have shifted over time. Circuits with tapped reactors rarely stay in balance indefinitely.

    Now, here's a practice question. You go out onto the floor and find a 460V motor with phase voltages of 458V, 465V, and 480V. Is there a problem or not? There sure is.

    Lowest voltage is 458V. First, calculate your four percent. 0.042458V 418.32V. The difference between the highest voltage (480V) and the lowest voltage (458V) is 22V (480-458). Since the difference (22V) is greater than 4% of the lowest voltage (18.32V), the phases are too far out of balance to ensure continued, reliable operation of electrical equipment.

  11. #11
    Join Date
    Dec 2002
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    SouthEast NC ICW & Piedmont Foothills
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    7,622
    is motor multi-voltage?


    when you get the next motor.........ohm it out

    have mfg give you the spec resistance of windings
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  12. #12
    Join Date
    Dec 2009
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    Buffalo, N.Y
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    single phase, 400 amp service. Start windings do de-energize, motor reaches operating speed.

    Multi voltage motor, 115/208-230. Ohmed out 1st and 2nd motors. checked capacitors on all. the newest motor, I regret to say, has not been read with an ohmmeter. I condemned the second motor even though it still ran and capacitors were ok. I assumed breakdown of the winding insulation due to operating characteristics, repeated OL trips and winding appearance. I guess I got complacent with the third motor and frustrated when it showed the same operating parameters as the previous motor(which I had condemned based on these parameters).

    I have not asked for specs on winding resistance, that's a good idea. I'm sure I can get those.

    The most troubling part, I think, is that I was able to achieve proper amp draw in the past. This tells me something has changed, I want to say incoming power, but if voltage and frequency are correct, I'm back to square one.

  13. #13
    Join Date
    Jul 2007
    Posts
    81

    Question

    It almost sound like it is miswired if it draws FLA without any load on the motor.

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