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Thread: Mysterious vibration in long conduit between solar inverters and main service panel

  1. #51
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    Quote Originally Posted by cowboyjwc View Post
    You sure that roof mounted AC units aren't causing the pipe to vibrate, since it sounds like it's hung from the underside of the roof. You say it's worse in the afternoons when the AC's would be running more.


    I'm kind of a look at everything guy.
    That's a great question but we're in a unique temperate coastal climate. 70°F is considered a hot day, average year round temps in the 50's. There are heat pumps up there but AC loading is very minimal here. Aside from that, the audible effects are highly transient and there is an extremely strong correlation to when the PV system is rapidly ramping up as clouds clear away, then it will rapidly fall off as clouds move back in, all of which tracks 100% with observable inverter data, current readings, etc.

  2. #52
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    Quote Originally Posted by Redwood Infrared View Post
    That's a great question but we're in a unique temperate coastal climate. 70°F is considered a hot day, average year round temps in the 50's. There are heat pumps up there but AC loading is very minimal here. Aside from that, the audible effects are highly transient and there is an extremely strong correlation to when the PV system is rapidly ramping up as clouds clear away, then it will rapidly fall off as clouds move back in, all of which tracks 100% with observable inverter data, current readings, etc.
    Have you tried opening the PV AC disco or interconnection breaker when the noise is occurring to see if it stops immediately?

  3. #53
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    Quote Originally Posted by ggunn View Post
    Have you tried opening the PV AC disco or interconnection breaker when the noise is occurring to see if it stops immediately?
    Yes, and before they brought me in they actually did a test where they turned off the inverters 1 by 1, then brought them back online in reverse order. Regardless of whether it's a function of insolation or # of inverters, there is a strong correlation between the sound level and net current.

    I feel a bit dumb for realizing each day there's yet another app for the smartphone I hadn't thought of but on my next visit I'll deploy my new Android vibration analyzer and try the sequential inverter shutdown test again to verify whether there's a correlation between current, vibration intensity, and hum volume. I imagine I will also see a relationship between mechanical vibration and audio frequencies as well.

  4. #54
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    Quote Originally Posted by Redwood Infrared View Post
    That's a great question but we're in a unique temperate coastal climate. 70°F is considered a hot day, average year round temps in the 50's. There are heat pumps up there but AC loading is very minimal here. Aside from that, the audible effects are highly transient and there is an extremely strong correlation to when the PV system is rapidly ramping up as clouds clear away, then it will rapidly fall off as clouds move back in, all of which tracks 100% with observable inverter data, current readings, etc.
    Gotta throw it out there sometime, I once walked up on two electricians an and engineer trying to solve a problem on why a motor wasn't working, I asked if they checked to see if a mouse had gotten in and chewed on the windings and shorted it out, they all laughed and kept checking stuff, I asked again and they told me that if I wasn't going to be serious I could leave. I told them I was serious and they asked why? I said because I can see the mouse and the arc mark it left on the side of the motor. Sometimes the simplest answer is the one.
    I can build anything you want if you draw a picture of it on the back of a big enough check.

    There's no substitute for hard work....but that doesn't mean I'm going to give up trying to find one.

    John Childress
    Electrical Inspector
    IAEI / CEI / C10
    Certified Electrical Inspector

  5. #55
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    Quote Originally Posted by cowboyjwc View Post
    Gotta throw it out there sometime, I once walked up on two electricians an and engineer trying to solve a problem on why a motor wasn't working, I asked if they checked to see if a mouse had gotten in and chewed on the windings and shorted it out, they all laughed and kept checking stuff, I asked again and they told me that if I wasn't going to be serious I could leave. I told them I was serious and they asked why? I said because I can see the mouse and the arc mark it left on the side of the motor. Sometimes the simplest answer is the one.
    One thing that's true of infrared thermography that I've found is really a pretty good basis for a personal philosophy is that many subjects emit frequencies we can't see with the naked eye. It is helpful to shift one's perspective by whatever means available so that the broader spectrum can be made observable.

  6. #56
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    Redwood Infrared:

    When working with electronic transducers you need to make sure that unwanted signals are not what you are observing.

    You mentioned seeing 120 Hz in your cellphone acoustic measurement. This I can expect from 60 Hz single phase. I don't know how likely it would be to see this as dominate from three phase wiring.

    High electric and magnetic fields might couple directly into your cellphone transducer and obscure any acoustic signal. This is why I suggested you might want a non-electronic transducer right at the cable and sound pressure coupled via a plastic tube to a more remote electronic transducer. I have not played with such a method.

    Also note that acoustic tubes can create resonances. A tight wire might be a useful sound transmitter. Mechanics use screwdrivers to couple engine or other noises to their ear.

    If you have a sound level change as you move along a conduit, then you might have a mechanical resonance of a length of conduit. I don't know what to expect, but changing mass on the conduit can change the resonance point, or added damping material can change the amplitude. Both mass and damping material will change resonance. Changing the resonance point also changes the amplitude .

    .

  7. #57
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    My guess, some sort of resonance created with the setup between the wire AC current and the metal (magnetic) EMT.

  8. #58
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    [QUOTE=Redwood Infrared;1922579]...did a test ....QUOTE]

    Think we all are breathlessly awaiting anyof that test data to be shown. Sure would be helpful to share an audio waveform, voltage and current waveforms.

    Need to have something factual on which to base conjectures vs. just that it drives folks out of the office.

    All we have so far factual is that something makes noise and it is related to the level of sunshine and the inverter model number.

    Would be great if you could get a release to share the THD, voltage, and current measurements taken by the poco.
    Last edited by junkhound; 06-13-18 at 11:32 PM.

  9. #59
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    Great discussion. I would like to know how this all plays out in the end.
    One thing I have learned thru the years (48) in T-shooting problems is that my mind tends to think of the most complicated reasons for the cause of the failure. When all is said and done it usually turns out to be something simple. I would like to know if this is a normal reaction and have others felt the same way.
    But I will not rule out the times when I have pulled my hair out on some weird problems....ha!
    Am I in shape?? I get plenty of exercise pushing my luck!!

  10. #60
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    Quote Originally Posted by ATSman View Post
    Great discussion. I would like to know how this all plays out in the end.
    One thing I have learned thru the years (48) in T-shooting problems is that my mind tends to think of the most complicated reasons for the cause of the failure. When all is said and done it usually turns out to be something simple. I would like to know if this is a normal reaction and have others felt the same way.
    But I will not rule out the times when I have pulled my hair out on some weird problems....ha!
    Yes, minor things like the shipping hardware not loosened or removed on AC Units at installation.
    Tom
    TBLO

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