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  1. #1
    Join Date
    Apr 2008
    Posts
    166

    Anyone heard of VFD noise emanating from the exhaust wheel?

    Anyone heard of VFD noise emanating from the exhaust wheel?
    I was called to look at some Greenheck exhaust fans at this site.
    A few of the twelve fans recently put on line have what sounds like VFD induced noise very easily heard, but coming from the wheel, below the motor and housing.
    These are Greenheck GB-330-30-X (page 40 in pdf link
    http://www.greenheck.com/media/pdf/c...GB_catalog.pdf

    Above at the motor area, there is very little noise at all, belts bearings all running smoothly.

    This does not sound like air whistling’. It sounds very much like the noise you would hear typically from a VFD itself, or the motor -but much louder.
    I read in some searches that the VFD switching frequency noise can be transmitted into wiring or from the motor into other parts.
    - I tried relaxing the belt tension while at 100% drive (to the point of obviously loose’ but not slipping) with no difference in the noise.
    - I compared two units that do this. With both at 100% drive both have the exact same pitch (‘note / frequency), and both have the same but lower pitch when at 70% drive.
    As well I spoke to a Greenheck support tech, he had not heard of this.

  2. #2
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    4,269
    Sometimes vfds have certain ranges they make noise.

    For example, 34-36hz a motor might be noisy. You can program the drive to skip 34-36hz to eliminate the noise.

    Put the drive in hand and see where it makes noise and program the drive


    Sent from my iPhone using Tapatalk

  3. #3
    Join Date
    Aug 2014
    Location
    DC suburbs
    Posts
    75
    As gravity mentioned you might be hitting the motor's resonant frequency. If that doesn't help, go into the parameters and experiment with different carrier frequencies.

  4. #4
    Join Date
    Jul 2005
    Location
    south
    Posts
    598
    Had the same issue on a new 40 ton Carrier ahu with a ABB vfd.
    Had to change the switching frequency from 4khz to 12khz before the noise went away.

  5. #5
    Join Date
    Oct 2011
    Location
    East Charlotte Area of NC
    Posts
    461
    Speaking of vfd's.

    I have one that I have to go look at Friday one of my techs ran across at one of the big marts on the condenser. We had a power issues during a storm and had to replace all the contactors in the vfd control panel. Well now when the vfd is running the motors seems to over heat and cut out on thermal so they are in bypass. He was getting some weird voltages on the output of the vfd, which is normal with a dmm due to it is basically pulsed DC voltage.

    My question is how do I diagnose this thing? From what my tech was telling me there are no alarms on the vfd, and it shows the hz it is supposed to be running at, but how do I determine if we have a bad vfd or something else going on?

    I have tried the almighty google, but alas it has for once been of little help.

    Anyone out there that can guide me?

    A slave to the great and powerful "product"

    I can't fix it if it won't stay broke..

  6. #6
    Join Date
    Aug 2014
    Location
    DC suburbs
    Posts
    75
    What happened to the contactors? I think you will find that some of the output devices are cooked on the drive. Maybe look to see what currents the drive is reporting.

  7. #7
    Join Date
    Oct 2011
    Location
    East Charlotte Area of NC
    Posts
    461
    The contactors are all 120v coils run off of a transformer. All the coils fried (amazingly the transformer is ok) and the 2 contactors that close on vfd operation had welded contacts.

    I am pretty sure that the drive has some issues, but big mart is going to ask how I determined the drive is bad.... and I wanna sound smart lol.

    I am a regional manager, and when it comes to racks it is hard to beat me (although there are some smarter than me on HVAC Talk), but I have never been trained on vfd's.

    A slave to the great and powerful "product"

    I can't fix it if it won't stay broke..

  8. #8
    Join Date
    Aug 2014
    Location
    DC suburbs
    Posts
    75
    Doesn't sound good. Tell them about the output devices and there is too much DC getting to the motors. I'm by no means an expert on drives but I know their basic operation.

  9. #9
    Join Date
    Oct 2011
    Location
    East Charlotte Area of NC
    Posts
    461
    I don't remember the numbers exactly... but my tech said he was reading 735v l1 to l2, 134 l1 to l3, and 65 l2 to l3. (The 735 did not bother me as much as the variance... he was reading with a dmm and they go wonky trying to read the output as its pulsed dc)

    If he had read 735 on all three I would not suspect the drive, but it's the variance that has me pointed to the vfd.

    A slave to the great and powerful "product"

    I can't fix it if it won't stay broke..

  10. #10
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
    Posts
    4,461
    735 VAC even on a regular meter is still waaay high. i use my True RMS meters on drives quite often, while they are not perfect, they still get fairly close.

    to truly see what is going on, you will need a scope meter. 1 thing to check is the incoming power and amperage. your meters should see that pretty good. if it is going goofy going in, then it won't be much better coming out. Also check your Bus Voltage...low bus voltages will indicate a bad capacitor bank or other issues.
    How to make the perfect "Half-Hitch" knot or any other boyscout knot in 3 easy steps...

    1. Remove your meter leads from the meter and very carefully return them to their storage case or bag.
    2. Wait 2 seconds
    3. Very carefully remove your meter leads from their storage place and enjoy your new knot!

  11. #11
    Join Date
    Oct 2011
    Location
    East Charlotte Area of NC
    Posts
    461
    Incoming voltage is 468v +/- 1 volt. Have not checked incoming amps.

    A slave to the great and powerful "product"

    I can't fix it if it won't stay broke..

  12. #12
    Join Date
    Jul 2011
    Location
    Lehigh Valley, PA
    Posts
    465
    Well now when the vfd is running the motors seems to over heat and cut out on thermal
    VFD's have axial fans. Are they working? I've seen bad fans cause units to overheat along with dust buildup on the heat sinks.

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