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Thread: out of ideas

  1. #170
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    Quote Originally Posted by tipsrfine View Post
    This is the part of the book about a motor being self-cooled. Notice the part about it being able to go over 30% as long as it's being sufficiently self-cooled. This does not contradict anything about my last quote when you go over the extra allowable 30%. It will still overheat after the 30% is exceeded even with the "self cooled" factor.

    Load Factor should not be confused with the common
    motor term called Service Factor. Service Factor pertains
    to self-cooled motors, such as the ones designed in accordance
    to NEMA. Service Factor is the percentage over
    nameplate horsepower that a particular motor can be operated
    at while being sufficiently self-cooled. For example, a
    1.3 rating relates to a 30% reserve in horsepower that can
    be drawn on if needed. This is useful when intermittent
    overloads will be encountered.

    But I don't really care, nor am I arguing any point about why or why don't motors overheat. My only point is it is not the result of pulling excessive amps when unloaded.
    I don't know what contradiction you mean. But I agree with the fact you just posted. A self cooled motor, meaning one that has a fan inside the housing, not an air over condenser fan motor, can be run at the service factor from time to time and will not fail. However if you run it at the service factor all the time, you will eventually lose the motor.

    I'm dying to find out where his problem is. I agree with others who have said he's got a problem in the wiring. I once had one where some guy had wired two speeds hot at once. The motor pulled almost twice name plate amps and if not for a wire in a twinning kit burning in half, the motor would have died. So maybe he's got something like a short across a fan board and he's feeding on two speeds.

  2. #171
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    He also had a pool cover motor go out that was recently installed. I asked him what did the blower motor have in common with the pool cover motor, but he never got back with me. We may never know since he basically got called an idiot in some of the earlier post. I think he thinks we're weird.

  3. #172
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    Tips,

    Honestly, I am not certain of my expected conclusions to this topic. I hope to find an answer that is something in-between the current debate, perhaps a comprise, that all I can expect. This will be a test using a motor similar to the motor in the OP (squirrel caged asynchronous induction signal phase); the conclusions may be different using other design applications.

    The slip ratio is the key, an unloaded motor offers less slip; the laws imply higher currents will develop within the stator’s field; increase current becomes heat which is absorbed by the internal components and dissipates into the surroundings. I do not think the increase in current equals full load amps, the torque will be limited to the rotor design, bearings etc., which is minimal at no-load. FLA is relized at full motor torque.
    Last edited by kdocsr05; 12-30-2009 at 10:38 PM. Reason: another typo
    Local 30 New York, New York Operating Engineer

  4. #173
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    Quote Originally Posted by kdocsr05 View Post
    Tips,

    Honestly, I am not certain of my expected conclusions to this topic. I hope to find an answer that is something in-between the current debate, perhaps a comprise, that all can except. This will be a test using a motor similar to the motor in the OP (squirrel caged asynchronous induction signal phase); the conclusions may be different using other design applications.

    The slip ratio is the key, an unloaded motor offers less slip; the laws imply higher currents will develop within the stator’s field; increase current becomes heat which is absorbed by the internal components and dissipates into the surroundings. I do not think the increase in current equals full load amps, the torque will be limited to the rotor design, bearings etc., which is minimal at no-load. FLA is relized at full motor torque.
    It sounds like you just said you expect the motor to pull higher amps after you take the belt off-is that correct?

  5. #174
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    No that is not correct. I expect the current to be lower than the loaded current.
    Local 30 New York, New York Operating Engineer

  6. #175
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    Quote Originally Posted by kdocsr05 View Post
    No that is not correct. I expect the current to be lower than the loaded current.
    Sounds good.

  7. #176
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    *

    I tested it today "again"

    my job today was going behind Testing and balance, and follow there advice

    the Test and Balance company had me replace a 2 hp motor with a 3 hp motor and a 7 inch drive pulley (which was bigger than stock) in order to attain the proper CFM

    i wired the motor before i mounted it because of it's location, then i thought about some of yall

    i fired up the motor without a pulley or anything on it

    FLA was 9 amps at 230 volts and 4.5 amps at 460 volts, my supply voltage was 230

    the motor drew 4.8 amps "unloaded"

    once i installed the non adjustable pulley, it drew 13 amps, as you know Test and Balance never gets this right the first time

    that's why i purchased an adjustable shiv while i was at the supply house the first time

    to finish the story, i installed the adjustable shiv opened up the shiv to attain an amp draw of 9.3 amps

    there was a 1.15 service factor so i called it done



    .

  8. #177
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    Well I wish you could have done that yesterday, would have saved me some typing.

    For the record this was a single phase squirrel cage motor correct?
    Last edited by kdocsr05; 12-30-2009 at 09:37 PM. Reason: typo
    Local 30 New York, New York Operating Engineer

  9. #178
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    Quote Originally Posted by kdocsr05 View Post
    Well I wish you could have done that yesterday, would have saved me some typing.

    For the record this was a signal phase squirrel cage motor correct?
    for the record this was a 3 phase 56y frame ao-smith motor



    .

  10. #179
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    Quote Originally Posted by Airmechanical View Post
    I tested it today "again"

    my job today was going behind Testing and balance, and follow there advice

    the Test and Balance company had me replace a 2 hp motor with a 3 hp motor and a 7 inch drive pulley (which was bigger than stock) in order to attain the proper CFM

    i wired the motor before i mounted it because of it's location, then i thought about some of yall

    i fired up the motor without a pulley or anything on it

    FLA was 9 amps at 230 volts and 4.5 amps at 460 volts, my supply voltage was 230

    the motor drew 4.8 amps "unloaded"

    once i installed the non adjustable pulley, it drew 13 amps, as you know Test and Balance never gets this right the first time

    that's why i purchased an adjustable shiv while i was at the supply house the first time

    to finish the story, i installed the adjustable shiv opened up the shiv to attain an amp draw of 9.3 amps

    there was a 1.15 service factor so i called it done



    .
    This was exactly what I had expected to read when I tested my motor unloaded, I will assume, however, by amp draw only, that yours was three phase. No answers yet, I have been busy elsewhere.

    I don't think you guys are weird, as earlier mentioned.I have been monitoring and reading your posts in my little spare time.

    I would love to get some of the key players from this thread together for some beers and watch what mayhem may unfold.

    Will definately post results or updates when I get back to the job. As of now, the customer is very busy at work himself and can't get the pool cover guys back to check their motor. He can't uncover the pool, He's happy with the "setback temperature" he is getting from only his radiant floor heat. Nobody's pushing the issue, and I only go where I'm told.

    Although I've gained a lot of respect for motor design, loading, and application, my money is still on a power supply issue.

    Again, thanks for the help, entertainment and sanity check (I'm good), I will keep this panel of experts informed.

  11. #180
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    3 phase!!! still may have some typing to do on this one.

    Good to hear from you fruecrue, after all your are the father of this on going debate



    Local 30 New York, New York Operating Engineer

  12. #181
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    Talking All in good fun.

    Quote Originally Posted by kdocsr05 View Post
    Well I wish you could have done that yesterday, would have saved me some typing.

    For the record this was a signal phase squirrel cage motor correct?

    poke.......poke......

    "SIGNAL" phase.....

    poke.......poke......

    typos are funny!

  13. #182
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    Quote Originally Posted by kdocsr05 View Post
    3 phase!!! still may have some typing to do on this one.
    it's the same for single phase!

    as stated, i have tested that before as well, but just not today

    i am all for having beers and testing motors, or just having beers, and Crown and Seven's



    .

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