Generate additional inverter capacity with a standby Multi

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1

Hello,

I have a grid-connected ESS with 3x MPII/48/3000, a Cerbo, 40 kWh of Pylontech batteries and 13 kWp of panels connected to 3x MPPT250.

I have a spare Multi, which I have configured in exactly the same way as the other three. In other words, all the MultiPlus units have the grid code (Austria) and the ESS Assistant. I don’t want to reconfigure the spare Multi so that I’ll be well prepared in the event of a failure in the future.

I would now like to switch this spare Multi to “inverting” when needed (when the Wallbox is charging), thereby increasing the total inverter output from 3x2400W to 4x2400W.

What do I need for this, or what would be the best way to do it?

I have a spare Cerbo. So far, however, I’ve been unable to get the spare Cerbo (the second ESS) to receive any SoC information. Passing through the BMS-CAN connection didn’t work.

Regards, Huafi

2

Good morning @Huafi

In a nutshell, that won’t work.

In a three-phase system, you always need the same number of MultiPlus units on each phase.

Adding or switching off devices isn’t possible.

I’ve never tried passing through the BMS CAN.

However, using the four Multi units via the MK3 interface should work. New functionality was added in the latest Venus OS version.

3

…thanks, I was thinking along these lines:

Have a single-phase ESS switched on as needed in parallel with a three-phase ESS.

This single-phase ESS should run with minimal resources.

It would already be enough if the Multi could switch fully to inverting mode.

4

Hi,

normally, it works if you loop the BMS-CAN through.

But there’s no problem running a second ESS in parallel with the first one. It doesn’t need any battery information for that, and if you do want that information, you can mirror the BMS from the first Cerbo to the second one. I did this on a Cerbo this week so that I can set the battery’s charging voltage for the Multi and start feeding surplus into the grid gradually before reaching 100% SOC. This works better than the old solution!

You can do the same for the grid meter to control the ESS’s power output, although I would prefer using a fixed negative power setpoint via the grid setpoint and Node-RED!

A lot is possible if you know how and are able to create the necessary Node-RED flows yourself or invest in additional hardware!

Bye

5

…thanks for the reply.

Perhaps my 2nd ESS didn’t work because I hadn’t connected an energy meter,
and the built-in current sensor didn’t measure anything because nothing was connected to it.
Do I absolutely have to connect an EM to the Cerbo to achieve surplus feed-in?
My aim is to operate the second ESS with 100% feed-in to the grid.
I would then switch this ON/OFF via a “contact” (Multi-Remote or the Cerbo INPUT).

Best regards

6

hello,

if you already have a smart meter, you can either emulate a suitable smart meter for the 2nd system via Node-RED, or control the ESS directly yourself; that can also be done via Node-RED.

bye

7

…I’ve solved it like this now:

4th Multi (48/5000), with its own Cerbo, EM540 and SmartShunt. As soon as ESS-2 receives a battery reading from the SmartShunt, it regulates as it should. On the new “branch”, I’ve connected only the WallBox and the heat pump. These are regulated to 0 by the second ESS (at least when the battery is charged), so the first ESS doesn’t see them as a load.