How exactly does a Victron Multiplus-II know that it can charge batteries?

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wytco0 asked Aug 15, '23

How exactly does a Victron Multiplus-II know that it can charge batteries?

Does anyone know what how a Multiplus-II knows that there is excess power available to charge its attached batteries?

I am having problems with my system where one battery is being drained to charge the other (see bottom for system details) I thought the issue was due to each inverter sensing grid demand and then responding and working again each other, and that is probably still partially the problem. However my assumption was that the inverter uses the meter or CT to see if there was excess power available which could be used for battery charging, but after additional testing I don't think this is the full explanation.

Following a suggestion in another thread I moved the CT for the Multiplus so it was upstream of the Growatt inverter hoping that it would respond quickly to instantaneous power demand and that the Growatt would only need to respond when the Multiplus ran out of power. However this does not really work and my original problem remains although its now more unstable. Before I moved the Multiplus CT this only seemed to happen one way with the Multiplus pulling from the Growatt but now it happens both ways but not at the same time.

As part of my investigation I removed the CT for the Multiplus completely, I though this would stop it from draining the other battery but it has not. So now I am wondering if there is another trigger such as voltage or frequency. I has a play with the grid set point on the Victron ESS settings and this did have an effect but it was unpredictable and may be the thing that causes the 2 inverters to flip which one is being drained and which one is being charged.

My System is:

Growatt SPH 5000 Hybrid inverter and 4.5kw of PV and 17kwh of Pylontech batteries - this has been in use for some time.
Victron Multiplus-II, Cerbo GX and 15kwh Seplos Mason battery - No PV

The Growatt measures the grid with a Eastron meter on the incoming supply and the Multiplus uses( a CT on the same tails but closer to the load.

Each inverter is connected to the main consumers unit on its own circuit. The Victron has nothing connected to the 2 output circuits.

Multiplus-II

2

2 |3000

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Alistair Warburton commented · Aug 15, 2023 at 07:27 PM

I am a little confused about what you are doing with the multi, given that it dosnt have any output connections, but I am assuming you have ESS set up and are using 'export' to feed your loads.

That is, well, an odd choice for a Victron but still.

The exactly part of your question would be the ESS configuration, which could be configured in many ways. Likely none of them aware of the the other inverter & battery.

I suspect your Victron is seeing the Growatt as a load and trying to support it but you are going to need to provide more detail. and a pic / diagram preferably.

If it were me I think I would b looking at some custom manager, node red on the GX perhaps, to drive the interaction of the two systems.

I cant give you speciffics, yet... No experiance of the Growatt system and insuficiant detail overall.

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wytco0 Alistair Warburton commented · Aug 15, 2023 at 08:07 PM

Thanks Alistair.

Yes I agree its an odd setup later I want to make the Multiplus handle most house loads and transfer everything but I can't do that at the moment as my consumer unit needs to be reconfigured to remove some high power circuits (ASHP and Car charger).

The current setup was done to try and allow me to use battery power to cover the house load for most of the day, currently the Growatt will only provide about 3kw so can't cover the kettle and the toaster at the same time.

I will do a diagram and post soon. At present the Victron is connected to its own MCB in my consumer unit and the Growatt is connected to a separate MCB. There is no PV connected to the Victron but there are 2 strings attached to the Growatt (which has 2 Mppts).

I am using ESS but I cant see anything in the parameters related to this sort of thing but I am new to the world of Victron. Currently it is set to charge the batteries during my cheap rate period if the attached battery is below 70%.

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