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Thomas avatar image
Thomas asked

How does a Multiplus II behave if no assistant is installed ?

I have red many Victron documents, watched webinars and also searched through the Victron Community but was not able to clearly figure out how a Multiplus II behaves if no assistent is installed. Would be great if someone could provide some informations.

Scenario 1:
- ACin of the Multi connected to the grid, no feed back to the grid
- Critical loads connected to ACout1
- One Pylontech US2000C and a Cerbo GX
- no PV, no MPPT

a) Will the Multi keep the battery always 100% charged?
b) Will the load on ACout1 fed from ACin or from the inverter by discharging the battery?
c) In case of a grid loss, will the load on ACout1 fed by the inverter and battery?

Scenario 2:
- Same as scenario 1 but additionall with PV and MPPT

a) Will the battery primarily charged by the MPPT and in case there is not enough sun via ACin?
b) Will the load on ACout1 primarily fed by the inverter by discharging the battery and in case there is not enough sun via ACin?

Actually I would like to set up a self-consumption system with backup capability and the possibility to charge the battery with an generator in case of a long lasting loss of grid. For this an ESS seems to be the right choice. But Victron says, that an ESS should not be used in case of "Off-grid systems - either with or without generator". That surprises me because a long lasting grid loss leads to a kind of "Off-grid system".

Multiplus-IIESSAssistants
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Rob Duthie avatar image Rob Duthie commented ·
What country are you from? If connected to the grid, a grid code is required!!! in ESS systems to be compliant.

It will run, it will treat the grid a genset.

Yes you can run a genset in ESS mode needs to be a high quality genset Honda. With a transfer switch for failed grid change over.

Regards

Rob D

NZ

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Thomas avatar image Thomas Rob Duthie commented ·

Country is Germany. Yes, I understand that grid code is required. Good to know, that ESS should work with a genset if the quality of the voltage is ok.
Thank you for replying.
Kind regards
Thomas


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ajmacleod avatar image
ajmacleod answered ·

Without the ESS assistant installed in your scenario 1 the Multi basically works like a normal UPS; load on AC out 1 passed through from grid and battery kept charged; if the grid disappears the Multi switches to inverting to feed the loads on AC out 1 from the battery.

From your description I'm pretty sure ESS is exactly what you want, configured with a high minimum SOC to ensure plenty of run time should the grid be lost for an extended period. In this mode (e.g. ESS with minimum SOC set to 95%), the Multi will use power from the battery for AC loads until SOC reaches 95% when it will transfer seamlessly back to grid. At times where PV is available it will use that to recharge the battery and any extra PV will be used towards powering the AC loads.

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Thomas avatar image Thomas commented ·

Thanks for the good explanation. This gives me the confidence that required system can be realized as I already assumed.

Kind regards
Thomas

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