Multiplus II not starting after battery low voltage situation (not low voltage disconnect)

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Andy asked Dec 19, '22

Multiplus II not starting after battery low voltage situation (not low voltage disconnect)

I have a Multiplus 5000 connected to a 48V LFP battery bank with 860Ah. The MP is on FW 500 and is connected via a MK3 adapter to a Pi running Venus OS 3.00-8. The system is purely off-grid and has 4 MPPTs for DC coupling which do all the charging (MP charger is deactivated).
DVCC is set with Limit Charge Current and SVS activated.
The MPPTs and Smart Shunt are also in the Victron Smart Bluetooth Network (not sure if this clashes with the DVCC. Info out there is not clear, but the system is running fine with both enabled and configured).
I have also two (the same) assistants installed and configured to start a 'generator' (which is in fact a Phoenix inverter). The rules kick in when the MP is under heavy load and the 3KVA Phoenix provides an additional 2kW of AC input for the MP, just like a gen would. This all works fine since the installation.

Here is the problem:
I deliberately ran the battery down to test out the low voltage behaviour of the whole system.
The Settings for the MP are as following:
DC input low shut down: 37.2V
DC input low restart: 43.6V
DC input low pre-alarm: 43.6V

(I set low voltage disconnect that low on purpose as I don't want the MP to shut down at all at the moment. This will be re-configured later.)

With a 2kW load connected, the MP shut down itself at 44V battery voltage. It showed a low battery light at the front. This was in the morning at 7am. At this time the MPPTs charged already with 1kW and could quickly rise the voltage of the battery again to over 50V charge voltage. Neither the BMS nor another DC connected inverter shut down, so the battery was low but not critical low in any way.
The MP did not start itself any more after the initial disconnect and still showed the Low Battery alarm at the front panel. When going into the MP through the remote console, it showed the actual DC voltage correctly, but under Alarm Status, it was showing an alarm for Low Battery Voltage.

Once the battery hit 50%SOC (~54.5V), I turned the MP off and on again which fixed the issue right away and it worked normally afterwards.

I was wondering why the MP did turn itself off in the first place but did not restart itself after the voltage in the system rose again. I would have 100% expected that. This is an extreme uncomfortable situation, knowing I would have been without power in a real scenario.

Thanks everyone.

Multiplus-II low battery warning

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klim8skeptic ♦ commented · Dec 19, 2022 at 05:51 AM

Post a link to the video.

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Answer 1 · 2022-12-19T05:12:14Z

Alexandra answered · Dec 19, 2022 at 05:12 AM

@Andy

I can't answer why is did not restart but do have the theory that because it shutdown before the restart value, it would have been in a fault condition.

The other theory is if you are using ESS then it shut down on one of those values related to load. And again because the restart voltage was lower it created the problem.

Did the systen log an fault or show a fault at all? Sometimes you can only see it in the csv data.

The smart network information is ignored by the mppts if they are connected to a GX device and you are using DVCC. See FAQ5

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Alexandra ♦ commented · Dec 19, 2022 at 05:58 AM

Another thought, have you set shutdown on SOC at all?

If you have smart batteries sometimes discharge current limit would have diactated a shutdown.

Is the 'generator' sharing the battery with the inverter as well? Maybe the voltage dip from that prevented the restart? It gives it three retries.

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Andy Alexandra ♦ commented · Dec 19, 2022 at 10:39 PM

Thank you for your quick reply and ideas.

The theory with the battery voltage being above the set input low restart could be why the MP did not turn on again. Good point. I'll test this out again and have now set the restart voltage to 48V.

I have not setup any shutdown on SOC and no smart BMS is connected.

The 'gen' is connected to the same battery but both, the MP and Phoenix are connected with 70mm cable to the battery bank which is 3m away. The Phoenix was not running at this time.

Not sue if the Smart Shunt is considered as a Smart Battery Sense as such as mentioned in the FAQ5...

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Answer 2 · 2022-12-19T06:35:49Z

JohnC answered · Dec 19, 2022 at 06:35 AM

Hi @Andy

Two sources of wonderment..

"The MPPTs and Smart Shunt are also in the Victron Smart Bluetooth Network (not sure if this clashes with the DVCC."

"why the MP did turn itself off in the first place but did not restart itself after the voltage in the system rose again."

Using the bluetooth network alongside the wired GX (VenusOS) isn't recommended. Victron probably don't even test for interactions given it's unnecessary to use both anyway. Alex's link to FAQ5 applies only to the Smart Battery Sense, and I wouldn't read too much into that.

Turn off the bt networking. Doesn't mean you can't access them via bt, just don't network them. I hope this is actually your issue, as following recommendations is an easy fix.

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Andy commented · Dec 19, 2022 at 10:47 PM

Hi John, thanks for your reply and assistance.

If I take the MPPTs and smart shunt out of the Bluetooth network, all these devices are not managed at all, not synchronised and are 'Standalone' devices. It shows this in the actual device when connecting via the remote console. So. the Ve.direct connection alone does not do anything in terms of grouping or controlling.

They need to be either controller via the BT network or the DVCC. As per your advice, I have now deleted the BT network but left the DVCC on and all controllers now show the external control (same as they did before with the BT still enabled). Not sure if this is the actual problem of having the MP shutting off above the set low voltage disconnect, but it's worth a shot.
Thanks again, John, appreciate your insight.

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Answer 3 · 2022-12-19T07:54:26Z

ditmarco answered · Dec 19, 2022 at 07:54 AM

Olá

Quando atualizou o firmware do MP II, verificou se as configurações ficaram as mesmas com o VE configure?

a atualização do firmware foi com um cabo ligado ao PC ou via portal VRM?

Marco

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Andy commented · Dec 19, 2022 at 10:49 PM

I did the firmware update via the VRM and re-configured the MP and assistants afterwards as it always resets to factory default. This is quickly done for me as I use the MP only as an inverter at the moment and don't need to change many settings.

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ditmarco Andy commented · Dec 20, 2022 at 10:04 AM

Via VRM, e se energia é perdida pelo portal que é feito o update, não cria o arquivo para fazer upload das configurações sem ter que estar a configurar de novo.
Congrats

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Answer 4 · 2022-12-21T04:55:12Z

elvis answered · Dec 21, 2022 at 04:55 AM

The smart SCC are V.E Direct connected and should be controlled by the GX and Multiplus. I dont think you should be using the SCC as independent device's.

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