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After an upgrade to my home's solar array, transformers in three devices in the home began physically humming: A transformer for the lighting in the kitchen range, a transformer in an audio amplifier in my home entertainment system, and a transformer in my linear RF power amplifier for my amateur radio.

The hum from each device is purely mechanical: There are no perceptible RF effects or any detectable hum coming from the speakers. Yet it is loud enough that it can be heard across a quiet room. Each device is located in a different part of the home, on separate circuits.

As a cross-check, I took two of the devices to a neighbor's house and verified the hum was gone at his location.

The manufacturer of the Ham radio power amplifier, which is based in the US and is known for its excellent customer and technical support, feels the problem is "dirty" (non-sinusoidal) electrical wave forms or "a bigger problem with your home's power system." Specifically, they state a Power Factor less than 0.95 could be an issue.

This is a new home that originally had a small solar array with Enphase microinverters and Hanwha 400w panels. The problem coincided with commissioning of the upgrade, which included an additional array comprised of more Enphase microinverters and Hanwha panels, as well as two Tesla Powerwall 3 batteries and associated Tesla controllers.

It seems obvious the problem is related to the solar upgrade. But before taking it up with the installer, I'd like to more clearly define the problem. I have an oscilloscope, but am reluctant to use it to measure the waveform of my mains electricity. I also own a nice Fluke multimeter (not a clamp meter). What measurements can I make to determine what is outside of spec with my home's electrical system so that I can more intelligently interact with the solar company, and hopefully, address the root problem?

GrowlTiger
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2 Answers2

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Yeah I had something a bit similar after adding batteries to my solar setup (not Tesla but still). Some devices started humming but only when solar was active during the day.

If you’ve got a Fluke multimeter, you can already check if your voltage is a bit high. I was getting like 252–254V sometimes, and apparently that’s already too much for some transformers.

Also if your meter does frequency, worth checking if it drifts from 50Hz or 60Hz. Mine was stable, but I’ve heard inverters can mess with that sometimes, especially when several are working together.

You could try plugging one of the noisy devices into an EMI filter (like those small ferrite blocks or a power strip with filtering). Just to see if the hum gets better.

Best would be to ask your utility (or electrician) to run a power quality check — total harmonic distortion, waveform shape, power factor, that kind of stuff. That’s what convinced my installer to take a second look.

Let us know how it goes — it's clearly linked to the upgrade.

ohyeah
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The "buzz" almost certainly is caused by sharp transients in the non-sinusoidal waveform from the added inverter.

You have a few choices:

  1. Get an inverter that produces a closer approximation to a sine wave.
  2. Put a filter in series with the affected devices to block higher harmonics.
  3. If feasible, bypass the inverter, deriving power, instead, from the AC mains.
  4. Add acoustic isolation. For example, mount transformers on rubber shock-mounts; create enclosures, being careful not to cause overheating.
  5. Move the devices to a location farther from the bedrooms, and endure the noise during the day. Likely, it's not causing any harm.
DrMoishe Pippik
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