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sahkovirta avatar image
sahkovirta asked

Voltage cycling up and down

I have a Victron ESS system installed (in a developing country), with 2 MultiPlus-II units (for 240V), a Cerbo, panels, and batteries. Over the past month, I've been seeing some strange behavior and haven't gotten much help from the installer, so I was hoping someone could help point me in the right direction as to what can cause this or what troubleshooting steps we can take.

See the video below for what I see the majority of every day. L1/L2 voltage on the grid ramp up and down (in the range ~114-128) in a constant cycle, along with L1 in AC Loads spiking to 2500W and going back down to 0W in the same cycle. This happens regardless of high or load load in the house. If I disconnect the grid (with a breaker), the problem immediately goes away and everything works as expected. If I reconnect the grid, the problem comes back. If I switch off the entire Victron system (feeding the house with grid power directly), the voltage wobbles maybe 1-2V, but nothing like it does when the system is connected.

What could cause this behavior? I've read about an open neutral somewhere causing similar symptoms, but usually with more extreme voltage variation?


Multiplus-IIESSgridvoltage
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2 Answers
Alexandra avatar image
Alexandra answered ·

@sahkovirta

Hi from another developing country. Diagnosis over the internet is a shit in the dark, but some of the causes are....

You likely have a weak grid connection. Or a high resistance connection.

Possibly a problem with a neutral. Could be from corrosion.

Wiring to the DB board is undersized.

Obviously I don't know the details of the install but these are some likely causes.


ESS does sort of a push pull with the grid based on the loss of mains detection that was chosen. So it makes some of these things more apparent.

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sahkovirta avatar image sahkovirta commented ·
Very interesting thanks! I'm reading about LOM detection and didn't realize all that was going on, that definitely sounds like it could be it.


Is it documented how long that "push/pull" cycle takes? I'm wonder if it matches the cycles in the video above.

Is there something specific I can ask the installers or an electrician to check in terms of a "weak grid connection"? Is there a way to measure that impedance directly/indirectly? Or I guess it sounds like they can temporarily disable and re-enable LOM detection and see if that eliminates the issue.

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Alexandra avatar image Alexandra ♦ sahkovirta commented ·

No it does not say. And I can say every site is different anyway in my experience.


Grid impedance test is usually the one. Sometimes a visual check works as well, my home has about 5 joins on the cable (tree branch related breaks) so is a pretty nasty high impedence connection.

Corrosion is usually visible if you go up and inspect pole connections.

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sahkovirta avatar image sahkovirta Alexandra ♦ commented ·
Grid impedance test sounds like something the utility would be doing with special equipment? The installer said they can test disabling and re-enabling LOM, so we can confirm that's the problem. If it is (and there's no obvious corrosion or anything), it sounds like the only solution is installing an expensive anti-islanding box and keeping LOM off on the Victron side?
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sahkovirta avatar image
sahkovirta answered ·

Working with the installer, we eventually disabled ESS and instead set up Virtual Switch Ignore AC to keep the grid completely disconnected except when the battery is low. That's just a workaround (it would be great to keep using ESS), but it seems to have basically resolved the issue.

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Alexandra avatar image Alexandra ♦ commented ·
@sahkovirta

Glad you have something that works. Yes I have used that as an option on a few sites as well.

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