question

wheeto avatar image
wheeto asked

Multiplus II overload

Hello,

I have a pair of MultiPlus II inverters in parallel on a single phase, running in ESS mode. When I switch a large (12KW) load on, most of the time the system works as I'd expect: the MPs deliver about 8KW, and the grid shows about 4KW incoming. Occasionally, though, I get the error below. How can I prevent this overload happening? I understand that if I turned on a 12KW load in a "grid lost" scenario it would cause an overload, but surely in ESS the system should be smart enough not to "overload itself"?

Thanks for any advice,

screenshot-2024-01-30-at-214313.png

Multiplus-II
screenshot-2024-01-30-at-214313.png (73.8 KiB)
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2 Answers
nickdb avatar image
nickdb answered ·

First and foremost, the ESS delivers from battery. As a low frequency inverter, it also takes time to ramp since it is not running in passthrough.

You are also assuming both inverters are running perfectly balanced, and not considering that there could be an additional surge that is not being displayed via the slower metering but that exceeds specs.

So, switching such a large load can cause a transient overload.

You also have to consider if the battery (you fail to describe what you have) is coping with the surge, that can also contribute.

Then there is temperature, which can also derate devices.

All in all, that is not an ideal design for that use case.

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wheeto avatar image
wheeto answered ·

Thanks for your reply. To A your Qs:

  • The inverter wiring is balanced according to Victron's instructions.
  • SOK battery pack is able to provide 400A.
  • Temperature is not an issue (environment around 10 degrees and inverters not loaded)
  • The 12KW load is pure resistive so shouldn't be causing surges etc.

What steps could I use to improve the design?

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