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which motor

Discussion in 'Compressors, Boosters & Blending Systems' started by abyss_scuba, Aug 15, 2017.

  1. CraigAClark

    CraigAClark Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: South Florida
    569
    32
    I have never seen a single phase, compressor duty motor where the rotation is "fixed". The RPM is critical as it is part of the formula to determine pulley size. Most motors used on these compressors are 3450 to 3600 RPM, as the compressor will rotate at 2300 RPM with 3hp motor and 1800 RPM with 2hp motor. With a 3hp it might not make much difference in pulley size, but you don't want to go beyond the recommended max RPM. Since the OP is in NY, I doubt the motor was 50hz. Where some motors can operate on both 50 and 60 Hz the RPM would be lower on the 50Hz, requiring a larger pulley.

    Another big consideration if you decide to use an alternative brand motor is the location of the capacitors. You don't want the capacitor covers on the compressor side of the motor. It/they might inter fear with the motor mounting holes in the base.
     
    Last edited: Aug 21, 2017
    RayfromTX likes this.
  2. cool_hardware52

    cool_hardware52 Dive Equipment Manufacturer

    7,582
    1,790
    General purpose replacement motors are often provide access to all the wires necessary to change rotation or voltage etc. The factory doesn't know the application and makes it possible for the end user to set these parameters.

    On the other hand motors destined for a specific application may not have all the required wires available in the junction box, and or may not identify them. Things can get a bit tricky if one is re-purposing a used motor.

    I would agree that in 2017 in the US the chances of having 50 hz AC from the "grid" is effectively zero. The US changed over from 50 hz to 60 in the 1940's and 1950's

    The RPM of an ac induction motor is a function of both the imposed voltage and the frequency. If you want to slow down an AC induction motor you need to reduce the voltage and the frequency. That's how VFD's or variable frequency drives work.

    Pretty much any "50" hz motor will run fine on 60 hz, just a bit faster, and any 60 hz motor will run fine on 50 hz, just a bit slower. There can be some efficiency loses if the voltage doesn't match, which can reduce the output horsepower and lead to heating, but if the motor is not being operated close to max specs it will probably be ok.

    In short if I had a "donor" motor that was 50 hz and my supply was 60 hz (or the reverse) I would give it a try before buying the exact right matching motor.

    Tobin
     
  3. CraigAClark

    CraigAClark Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: South Florida
    569
    32
    That is great, if you are the end user and DIY. However, if you are supplying a client, liability always rears its ugly head. It is also possible that someone in the USA or Canada could acquire a used compressor with a 50Hz motor. I have provided many compressors to yachts that are 50Hz. If a 50Hz yacht decides to sell a unit for what ever reason and it is purchased here.....
     
  4. cool_hardware52

    cool_hardware52 Dive Equipment Manufacturer

    7,582
    1,790
    If one is doing a motor swap on a professional basis you should of course stick to name plate specs and best practices.

    However this is a thread on SB, where the OP is seeking help with a DIY type repair.

    If the OP is actually a professional compressor tech, and he's seeking technical advice on SB then he needs to reconsider his chosen profession.........

    Tobin
     
    RayfromTX likes this.
  5. CraigAClark

    CraigAClark Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: South Florida
    569
    32
    My living is earned as a Mako and Bauer tech. I also work on the side in the yachting industry for a company that sells/services Nitrox Solutions products. I have been giving advice on SB for a long time and some think it has been useful. Don't really care if the folks reading my posts are DIY or professional.
     
  6. cool_hardware52

    cool_hardware52 Dive Equipment Manufacturer

    7,582
    1,790
    Craig, Do as you please. If you feel the need to protect your professional reputation so be it.

    I'm going to continue offer the type of advice that the typical "home brew" DIY type could find useful, i.e. The guy that just wants to get his compressor running at the lowest cost and isn't all that worried that his "kludge" might some day end up in the equipment hold of a mega yacht.

    Not sure why you can't tell the difference between these two distinctly different users........

    Tobin
     
  7. abyss_scuba

    abyss_scuba Dive Shop

    # of Dives: 500 - 999
    Location: Pleasantville, NY
    373
    210
    Thanks for all your replies. So here is the final outcome. Started taking the shroud off to replace the motor a n d found that when the motor was replaced the motor pulley was off set putting a strain on the pulley. Took the belt off and motor ran fine. Realigned the motor pulley with the compressor pulley and evrything ran fine. Ran the compressor for 5 hours and all seems good now. Sometimes it is a simple answer.
     

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