Multiplus II 48/5000: DC-Feed-In after switch from Absorption to Float

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martin-henning asked Aug 10, '23

Multiplus II 48/5000: DC-Feed-In after switch from Absorption to Float

Hi all,

we have a 3ph setup involving the aforementioned Multiplus, 3x Fronius Symo on ACout and a RS450/100 on the DC side.

I notice a pretty large DC_feedin after switching from Absorption to Float, which I cannot explain. AC and DC feed-in is allowed, all PV data is reaching the Cerbo, ESS is active and working. I don't see any reason for feed-in beyond the DC-coupled DC power - what am I missing here?

The effect lasts for roughly 2mins and the current is ramping down over time, as if something is being actively ramped down or some sort of equalisation is going on. You can see in the end of this screenshot:

I have now configured the float voltage 0.5V higher to see if it makes any difference tomorrow, but either way, I don't see a reason for such large feed-in beyond PV power?

Any explanation is appreciated :)

Tnx,

Martin

ESS feed-in limit

screenshot-2023-08-10-at-134354.png (751.5 KiB)

screenshot-2023-08-10-at-134533.png (497.1 KiB)

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Answer 1 · 2023-08-10T16:52:40Z

Michelle Konzack answered · Aug 10, 2023 at 04:52 PM

Ehm, you sayed:

I notice a pretty large DC_feedin after switching from Absorption to Float, which I cannot explain. AC and DC feed-in is allowed.

Hence where is the problem?

1) your batteries are full and the MPPT is in float

2) DC feed-in is allowed

3) the sun is probably shining

4) your MPPT can deliver more energy and it is feed-in.

There is nothing wrong with it except, that the MPPT deliver only 2048W, but the load on the battery is 4003W.

It seems, the DC feed-in is not correctly setup.

How did you setup the DC feed-in?

Without knowing your config it is hard to say, why it feed-in twice the energy from the PV

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Answer 2 · 2023-08-10T23:01:39Z

martin-henning answered · Aug 10, 2023 at 11:01 PM

Well, my problem is, that the battery is being discharged into the grid :) You can clearly see, that the feed-in consists of PV power minus PowerUsageInHouse plus batteryDischarge. Why and where should I explicitly allow this? What dc-feed-in setup are you talking about except for the two switches in the ESS menu? Why dies this behaviour start and why would it automatically stop? :) I have the feeling that the battery is being discharged into the grid until the lower float voltage has been reached. Not sure why, there is no need to do that, but that's the reason why I want to try a higher float voltage to see if this effect would be smaller the next day.

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Answer 3 · 2023-08-11T10:39:02Z

martin-henning answered · Aug 11, 2023 at 10:39 AM

Small update: The backfeed is much smaller with a higher float voltage. I raised float from 54 to 54.5V. This is no explanation for the effect itself, but at least something :)

screenshot-2023-08-11-at-123400.png (270.5 KiB)

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