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klandos avatar image
klandos asked

Adding a different Multiplus via ESS mode to Offgrid Installation possible?

Hey there,

following situation:
3x Multiplus II 48/5000 in parallel Mode, offgrid, controlled by a Cerbo GX and all PV DC coupled.

Battery Bank is Lifepo 130kWh usable.

I have a Multiplus 48/3000 GX laying (yes its already there and unused) around.

From time to time it would be nice to have a bit more AC Power on the system.

My question is now if it's possible to configure the Multiplus 48/3000GX in ESS Mode 3 and connect it to the AC out of the 3x Multiplusses5000 via AC In on the 3000. Disable charger completely and just enable discharge. I know that ESS Mode3 is configurable like that

In the Cerbo GX a "switch" (either relay or network/modbusTCP) that tells the Multiplus3000 to discharge with 3000 Watt wenn AC load is higher than 5000 Watt and to disable discharge when it's below 2000 Watt.

That way I would gain a nice AC boost. At the moment I start reducing loads (EV Charging, water heater, water pumps ...) when the load is above 9000Watt.


In theory this should work, but what happens when for a couple of seconds the AC Load is less than the 3000 watt that the Multiplus is feeding and does not stop feeding that fast?

In theory exactly same situation like with a AC PC Inverter that es feeding AC wise.

This would f.e. be the case when the EV Charging stops (drop of a 7kW load).

Will the 3x 5000er feed that energy back to the battery bank for that couple of seconds?

Thanks in advance!


Multiplus-IIoffgridess discharging
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5 Answers
Paul B avatar image
Paul B answered ·

You could add it as a standalone on a a out of the system. Keeping in mind that the pass through can't exceed its Max limit being 50amps for that model and I think you may exceed its Max pass through current. However. It also has to be separately controlled. You can't add it to the existing cerbo. You would have to control its power assist so that it would assist the combined output. It's a messy way to do it and if you are using the same battery bank. Then you will have complications there as well.


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klandos avatar image klandos commented ·

Hey Paul.

You can't add it to the existing cerbo.
- I don't want to do that. The only thing what I would like to do is enable/disable discharging of the Multiplus3000 by the Cerbo. Fo that I would like to read the dbus and control the 3000 by modbusTCP.
You would have to control its power assist so that it would assist the combined output.

That won't work in either way. That's why my thought of configuring it in ESS Mode 3 and "just" connect it over the AC In from the 3000. So I can feed in power AC wise.

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marv2097 avatar image
marv2097 answered ·

Yes in theory that could work but as Paul B mentioned it would be messy. I have been doing something similar recently to get a few multi's working together that are not part paralleled but I wanted them to be part of the same ESS system.

- Your 48/3000 would need its own GX device (i use a rpi running venus with a MK3 adapter).

- You then need something to control it, you may be able to do this with node-red on the main cerbo you have and send modbus to the slave GX device. Put ESS in `external control` mode and then send it a setpoint to register 37 (ESS power setpoint phase 1).

This is vastly simplified and not without its issues. I used a separate Golang application to read/write to the GX devices via modbus and while it worked well it it took some effort to get working in a reliable manner. Have fun!

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klandos avatar image
klandos answered ·

Hey Marv,

- Your 48/3000 would need its own GX device (i use a rpi running venus with a MK3 adapter).

Its a Multiplus 48/3000GX, so already integrated.

- You then need something to control it, you may be able to do this with node-red on the main cerbo you have and send modbus to the slave GX device. Put ESS in `external control` mode and then send it a setpoint to register 37 (ESS power setpoint phase 1).

Exactly this is my plan, I will prefer a litte bash script, but yes...


As you've done that:

Is there anything that I need to configure on the 3x Multiplus 5000 so that they will feed back from AC to DC for the short moments when a high AC load drop off? Or is that just the default behavior?


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marv2097 avatar image
marv2097 answered ·

Hi klandos, ah yes sorry i didn't see the mention of the GX.

In my setup I am grid connected so a little export doesn't cause an issue. As you are offgrid then I suspect there is a risk if the load goes away that AC voltage will spike to an unacceptable level if the ESS on 48/3000 cant respond quickly enough. I don't know know enough about how this would behave so if it were me I would start small and test cautiously. As you mentioned in your OP it does sound very similar setup to a AC coupled solar on AC out with grid down.

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klandos avatar image klandos commented ·

Reading here point 5:

https://www.victronenergy.com/live/ac_coupling:start

“

Multis and Quattros with factory settings will not shift the AC output frequency to regulate charge current. When setting up an AC Coupled system, install either the ESS Assistant (for grid-connected systems) or the PV Inverter Support Assistant (for off-grid systems).


”

It should work out of the box that excessive AC load will be feed automatically back to DC.

Could anyone confirm this?

The pv inverter assistant isn’t necessary for that as I dont’t need frequency shift, right?


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klandos avatar image
klandos answered ·

It should work out of the box that excessive AC load will be feed automatically back to DC.

Could anyone confirm this?

Or do I need any assistance active for that?

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