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danielj avatar image
danielj asked

Official Multiplus-ii 8-15kva parallel support?

Hi all.

I was going through the new Multiplus-ii external transfer switch manual that was released and noticed that it references using the Multiplus-ii for installations up to 180KVA.
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As far as I am aware there was no official support for the paralleling of the 8-15kva multiplus-ii units.
Does this mean that there is official support for the paralleling of the multiplus-ii 8-15kva units now?
Is it only applicable to the new configuration?

Multiplus-IImultiplus in parallel
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2 Answers
nickdb avatar image
nickdb answered ·

I need to correct the previous answer after inside info.

In short, the external transfer switch feature gets around issues preventing 8k and above units from operating in parallel, so yes, you can build large parallel systems with them providing an external transfer switch is used.


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danielj avatar image danielj commented ·
Thank you for the feedback Nick! I assume this only applies with generator setups and not grid connected?
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nickdb avatar image nickdb ♦♦ danielj commented ·

Yes, genset only due to certification requirements.

A grid compliant version is being planned and will require additional hardware.


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dmann avatar image
dmann answered ·

It's not totally clear from the documentation in the PDF or on Victron Professional website - does this remove the ability for the Multiplus ii unit's ability to charge the batteries from generator? It looks like small wire, around 16 awg is all that is needed on the AC input side of the inverter(s) in the documentation. Does this mean that they CAN NOT charge the battery with AC from the input side, or that it's optional to install larger wires on one of the inverters to keep the batteries periodically charged up?

I suspect that charging from AC input can't happen with the S99 firmware - could you please confirm this in the documentation?

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jdw avatar image jdw commented ·

Short Answer: Charging still works.

Long answer: The wires leading to the AC-Input are simply for voltage and frequency sense, not usable current. In practice, this method operates the MPII inverters bi-directionally via the AC-Output terminals. Similar to how a PCS BESS configuration would operate. The only difference being an external EMS would be reading the external V/Fr and signalling/modulating the PCS to match the external source before pulling in the contactor. In this case, the internal logic of the MPII is doing that instead. Frankly, this method/ability solves a lot of problems for us (installers) over using the internal transfer relays. Makes installations simpler.

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