Among the numerous things I’m – well, not phobic. I’d go no higher than ‘cautious’ – about are the sparky parts of DC power systems. Having seen a number of dramatic things happen in the 12-volt power systems of automobiles during my years as a dealership wrench and after, and being aware that even the smallest (ahem) of solar power systems make a car’s electrical system look like it’s run on AAA batteries, I always pay very close attention when dealing with big solar-powered storage batteries.
This is why I like working on Landlady’s batteries, because they have proper circuit breakers that can lock out both the input and output sides, isolating the batteries and reducing the arky-sparkies to basically nothing. This is good. Today, following up on the corrosion revelation of a couple of weeks ago, I wanted to pull apart the whole battery bank and clean and tighten all the connections. Step one: Turn off the inverter and open all the breakers between the batteries and solar panels.
I have known for many years that Landlady’s powershed is surrounded by a heavy EM field. I know because I listen to a lot of AM radio and when you drive the Jeep into the vicinity of the powershed you can hear the heavy RF interference. It’s a sort of bubble: Approaching the shed, whatever’s on the radio becomes inaudible due to the interference but as you park right next to the building the interference is attenuated but still audible. Flick the circuit breakers, and it goes away. I parked right next to the open powershed door so I could listen to the radio and pay attention to the dogs while I worked.
Pulled off the cables, cleaned and tightened the connections that needed cleaning and tightening. Flicked the breakers to the PV panels back on. Immediately there was a low-pitched whine, so loud that at first I thought it was coming from inside the building. The whine got louder and higher in pitch, louder and higher until I began to wonder (have you ever seen what happens when a lead/acid battery explodes? Because I have.) whether I should even be standing in there. I stepped toward the door, to find that the sound was coming from the Jeep, not the equipment. It rose further until it passed into inaudibility, and then there was just the normal level of interference.
Stepped over and switched the inverter back on: Everything was just fine. That rising tone, I imagine, was the EM bubble building and passing over the Jeep’s radio antenna. Lots of power in the powershed.
Wow, that’s a weird one, Joel. But told like the opening of a disaster movie. Or an SciFi epic: “Joel gets catapulted into an alternative universe.”
Interesting. The panels and the batteries should be straight DC so I have to assume that it’s the charge controller or the inverter. Switching supplies do put off some RF but either should be that noisy unless they’re old, on the way to failing, or running near capacity. Either way, I’d keep an eye on them. I’d worry a bit about the quality of the power coming out of there too…
No, the power coming from the panels is straight DC but it goes not to the batteries but to the charge controller, which I left out of the story. The power from the controller to the batteries is pulse-width modulated, so it cycles just as if it were AC*. So you’d get some lovely RFI.
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* All this information and more was imparted by that inspired political philosopher and not-even-close-to-an-electrical engineer Some Crazy Old Guy In The Desert, who taught me everything I know. 😉
Yeah, since the inverter was off it had to be the charge controller. The rising whine was the controller performing its search for the maximum power point from the panels.
I don’t think this is a sign of distress or age in the charge controller. Those long wires from the controller to the panels act as antennae for radiating the PWM frequencies.
IIRC the powershed has a metal roof; does it have metal walls? The bubble effect you describe might be because the metal roof acts a shield between the solar panels/wires and your Jeep radio antenna.
The walls are wood, but they do have mesh under the stucco.