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  1. #1
    Join Date
    Jan 2010
    Location
    Toronto,Ontario Canada
    Posts
    355

    Using a megger for hvac/r

    How many people here actually have a megger in their trucks and how often is it being used. i have a family member that says he uses it all the time in his jobs (of course hes a electrician) is it really worth buying one. or is ohming out a motor just as easy?

    thanks in advance
    Akelesis
    Get er Done!

    Do what has to be done
    when it has to be done
    as well as it has to be done
    And doing it all the time.

  2. #2
    Join Date
    Feb 2011
    Location
    Orange County, in a Galaxy far far away...
    Posts
    277
    I'm keen to hear the input on this thread. I could've used a megohmeter on 3 separate occasions this week, anybody on here got thoughts on brand, price functions etc?
    You cannot cheat an honest man. But that doesn't stop people trying!

  3. #3
    Join Date
    Oct 2009
    Location
    aiken s.c.
    Posts
    170
    I recently used mine to find a bad condenser motor that read o k with a meter.I will admit that i don't use it often,but in this case it saved the day!

  4. #4
    Join Date
    Jul 2005
    Posts
    5,511
    Quote Originally Posted by aikenite View Post
    I recently used mine to find a bad condenser motor that read o k with a meter.I will admit that i don't use it often,but in this case it saved the day!
    Care to elaborate? Was it tripping the breaker?

  5. #5
    Join Date
    Jan 2011
    Posts
    1,150
    Quote Originally Posted by JayGuy
    1000 volt is usually more than enough...i test ALL motors at 1000 VDC. yes, even 115VAC motors and they do just fine.
    Yeah, until you find one that the insulation is compromised. Industry standard for DC test voltages of 120-
    240 VAC motors is 500 VDC. Certainly you can continue juicing those little motors to 1000 VDC until your luck runs out.

    The manufacturers of 4160 V motors prefer a continuous application (10 minutes) of approximately 2500 VDC rather than shorter durations of 5000 VDC.

  6. #6
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
    Posts
    4,350
    Quote Originally Posted by KnewYork View Post
    Yeah, until you find one that the insulation is compromised...
    that's the goal. at 2mA DC of maximum current, lightning bugs have more power in their butts than a megger. no damage is going to occur unless it was already there to begin with.
    "Mother" is the name for God on the lips and hearts of children....The Crow

  7. #7
    Join Date
    Aug 2012
    Location
    Hot Springs, Arkansas, United States
    Posts
    55
    A good megger test can give you a heads up about a potential future problem. A good multi-meter is great for checking motor windings, bad connections, caps ect... I have seen a compressor fail a megger test and run for years.

  8. #8
    Join Date
    Oct 2001
    Posts
    6,965
    ohm'n out a motor is a different animal the megging out one.if you held the lead on a megger and pushed that red but it would take you off you feet,meggers test the insulation on the windings and the reading is the leakage of that charge in testing.big tonnage OEMs design their chiller for so many starts when the equipment sees 10X the rated amperages on start.the windings actually move and rub together...number of starts/hours run are a major log input with building engineers...100,000 ohms to ground is mint... solid...tight...new windings on any motor.as that number drops over the years 75,000>50,000 a burn out situation is in the future..and there is nothing a tech can do to fix that reading it being useage run time,to many restarts..add air within the system.. burn out clean up...water into chiller and that drops that numer also...
    "when in doubt...jump it out" http://www.youtube.com/watch?v=U1qEZHhJubY

  9. #9
    Join Date
    Oct 2009
    Location
    aiken s.c.
    Posts
    170
    On a carrier 50tc there are 4 condenser fans.They are fed by 15 amp fuses The fuses had blown several times and other guys would just replace the fuses and it would work for a day or two.I decided to find and correct the problem so I isolated each motor and megged the motors.1 motor gave odd readings compared to the other 3.We ordered a new motor and replaced it The unit has been working fine for a couple months.Like i said ,I don't do many start-ups so when I break out my megger I am looking for something unusual.By the way, the motor that was bad had a lot of oil inside as if the bearings were bad.

  10. #10
    Join Date
    Jul 2005
    Posts
    5,511
    Quote Originally Posted by aikenite View Post
    On a carrier 50tc there are 4 condenser fans.They are fed by 15 amp fuses The fuses had blown several times and other guys would just replace the fuses and it would work for a day or two.I decided to find and correct the problem so I isolated each motor and megged the motors.1 motor gave odd readings compared to the other 3.We ordered a new motor and replaced it The unit has been working fine for a couple months.Like i said ,I don't do many start-ups so when I break out my megger I am looking for something unusual.By the way, the motor that was bad had a lot of oil inside as if the bearings were bad.
    Repeated over amping and overheating of the windings could break down the insulation enough to show a difference in leakage current between that and the other identical motors. I wouldn't have thought of testing for bad bearings like that, but in hindsight the idea seems to have some merit despite its lack of conclusiveness. Thanks for sharing that.

  11. #11
    Join Date
    Oct 2009
    Location
    aiken s.c.
    Posts
    170
    I wasn't looking for bad bearings, that was just something that I did notice about the motor.As far as being conclusive the unit is working fine ,that's good enough for me.There are times when you're good and other times when you're lucky.I bought my megger at a pawn shop for around $40.00,but in this case I wouldn't take a gold quarter for it.When I started out I debated whether or not to get one but I couldn't pass this up.There haven't been many times that I have had to resort to this but I don't like to borrow things and it got the job done.Hope you have a great week!

  12. #12
    Join Date
    Jan 2011
    Posts
    1,150
    Quote Originally Posted by JayGuy
    no damage is going to occur unless it was already there to begin with.
    Like Tom Petty says "you can believe what you want to believe..."

  13. #13
    Join Date
    Feb 2011
    Location
    Orange County, in a Galaxy far far away...
    Posts
    277
    Maxster, any input as to a good "megger" for starting out? I work on everything up to 50tonnes at the moment.
    You cannot cheat an honest man. But that doesn't stop people trying!

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