kevstone122 avatar image
kevstone122 asked

When BMS Switch DC off and grid is available, why Multiplus Switch off the Full House (AC)?

I still cannot understand, why Victron switch off the AC Output, if the Batterie has problem, but still the Grid is available?
My full house is connected to an 3-Phase system and the full house run over the 3 Multiplus. If the DC Bus has some Problem, the full House will switch off because of the Voltage Ripple or Voltage minimum. This can happen at the beginning of an system to see how it works with the batteries!

So maybe BMS will switch off the DC Voltage!
BUT if there is an AC Input available, why the Multiplus cannot switch to the AC-Mode and just switch to the passthrough mode?

So house is off in this situation and grid is available make no sense for me!

Thank you!

Best regards

griddc system
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4 Answers
kevstone122 avatar image
kevstone122 answered ·

Hello Alexandra!

Thank you for your feedback!

Yes i have installed ESS system and of course we can adjust the BMS not so critical...but anyway i cannot understand why the system can not use immediately the Grid-Power...

It can Switch off the MPPTs over the ESS System and so the Victron system is just running in the passthrough mode, for my opinion! Also if i want to change Batteries and something else, for service i need to shut down everything!

So now i have installed an extra Basic Server UPS for my SmartHome-Control Unit and for Server System, because if Victron has Problem, i will not get any information from the cerbo and i lost communication...this is a little bit stupid!

If there will be inside a small transformer so create from 230V the 48V, then the Unit will be ON and finish...Like a parallel power supply of servers... So there is no change in the future about this?

Best regards


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shaneyake avatar image shaneyake commented ·

What batteries are you using? Do they have CAN bus coms to GX?

Victron system works well as a UPS and I have it running many businesses for this purpose.
The inverter can run in passthrough mode with no battery attached, just flip it into Charger only mode.

It is more likely that you are triggering an emergency shutdown of the inverter. This will turn everything off to prevent damage to the inverter. The inverter doesn't have a built in bypass system so in order for power to flow through the inverter the inverter needs to be fully online.

Let's work together to solve the real problem rather than blaming Victron for a safety feature that is important.

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kevstone122 avatar image kevstone122 shaneyake commented ·
Thanks a lot for your answer!

The LiFePO4 Batterie has just its own BMS and some Mosfets which switch off the Batterie connection to the Inverters.

There is a 12V Signal for charging and discharging. So i have this two signals. Can i connect them somehow to the inverters to tell them, now Batterie is not ready anymore? So the inverters change automatic in the only charge mode in 20ms....

You are right, the system just see undervoltage because batterie is disconnected from inverters because BMS switch off and with 0 Voltage the current will be high for the same power...

So how i can inform the ESS System, that Batterie BMS switch off?

Thank you a lot for this help!!!!

Best regards


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shaneyake avatar image shaneyake kevstone122 commented ·

Oh cool, Yes Two Wire BMS will work. You will need to install 12v relays that your BMS control and those relays can be wired and setup like the PDF below.

Does your BMS disconnect both charge and discharge fets at the same time? If so this might cause a problem. Is this a DIY battery, can you change the BMS? There are a decent amount of BMS that have full coms with the GX.

Orion or REC BMS have native CAN support as well.

On most systems the BMS can talk to the GX over CAN and would tell the system if there is any problem and then the inverter can react accordingly.

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Alexandra avatar image
Alexandra answered ·


The battery is the heart of the system.

The entire systems purpose is to look after that asset. If there is a problem with it then the system will shut down to protect both itself and your battery investment.

I would say that is a good thing.

Install a bypass switch that allows the loads to run directly offgrid and allow the system to charge and settle down if there are issues there.

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kevstone122 avatar image
kevstone122 answered ·

Hello Alexandra!
Thank you for your answer!

The Problem is, that the Victron system supplies the full house with the USV System and so i was thinking i don't need any other USV-System. If the Viictron system shut down, you have big problem with IT-Systems likes switches, server, Smart Home functions and you cannot "just start" everything again without problems.
The next point is the BMS of the LiFePO4 Batteries. If there is some parameter out of range, it should protect my Batterie and will open the DC-cable, this is good, but why in this moment the Multiplus should switch off? The BMS open the connection to the batterie and the systems thinks there is not Batterie anymore! There is no reason if the Grid System works to switch off the house just because of the small "Batterie-issue!
So the Batterie is the bottle neck of the system!

Is there maybe any differences if i change the voltage-measuring cable of the shunt after the BMS-contactor. So if it switch of, the shunt show the system 0V and so the multiplus will just switch to the "Main" mode and don't use any inverter?

Thanks for your answer!

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Alexandra avatar image Alexandra ♦ commented ·


Configure the multiplus to not use the batteries out of the parameters. I have never experienced a set up when correctly configured to have a battery shutdown before the inverter does.

With peak shaving and power assist as features of the inverter the battery is most critical. Do you have ess installed?

I understand about the IT equipment. I have server rooms running with Victron installed and running other critical systems. Some loads should never shut down.

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carsten2 avatar image
carsten2 answered ·

I also have this problem. In fact the current system is more instable with the Victron Multiplus II as a USV than before. I want to use the Victron II as USV in case of power outage.

But currently any problem with the battery, even if it is not a real fault but, e.g. just safety disconnect in case of cell overvoltage or cell undervoltage from the BMS, shuts down the whole Multiplus system also on the criticial load output even though grid is avaible making the system real unstable.

There is no reason to switch the Multiplus of just the battery is connected.

Is there any method of preventing this?

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shaneyake avatar image shaneyake commented ·
This is what is meant to happen, it is the safest option for all the equipment. You should never have a BMS faults.

Have you tried lowering the charge voltage in DVCC to prevent the cell overvoltage?
You need to set the inverter cut off voltages so that you never trip a BMS low voltage.

You could disable feed-in via the aux input which would prevent the inverter from tripping off if you did it fast enough.

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carsten2 avatar image carsten2 shaneyake commented ·

There is no additional saftely by powering everythiing off when only the battery is cut off. As the system can operation without any battery, there is no real reason to shut everything if including the pass-through from gid. The whole point of an USV is the provide uninterupted power supply to the critical loads, not matter whether the grid or the battery fails, or is switched of for any reason.

This is a bug, because it ads no no safety, but making the system more instable.

It is also a bug, that the whole system switches off, in case of the BMS just stops charging and signales an overvoltage condition. Instead the system just do what the BMS wants: Just stop charging. It could still discharge of power is need, but there is no reason to shutdown completely.

In Additionn, lowering the charge voltage does not help, because in the end cells tend to be non-balanced. But the main point is: The critial loads should only be switched off if both grid and battery fails.

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kevstone122 avatar image kevstone122 carsten2 commented ·

I totally agree with this opinion!!!

The system will be more unstable because of an battery issue, also if the grid is available. If the grid is available and there is a battery fault, i don't care about this fault. The BMS will switch off anyway in the worst case but house should be still on. Switch all the currents to 0 for Battery, maybe also switch off MPPTs i don't care. But Multiplus must be in pass-through mode...

This is an totally Bug which comes maybe from old lead battery without any protection. Any LiFePO4 Battery must have BMS and so it's okay if in the worst case BMS switch off, to still run Multiplus in pass-through mode.
If the system can switch from Grid to Battery below 20ms, then system should also be able to do it from Battery to grid, isn't it?


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olegv avatar image olegv kevstone122 commented ·


At least it's not normal, the grid power (if available) should never be switched OFF, it's exactly "UPS Mode" :). Moreover, there is the following problem, not only for me. It just says "Low Battery" and switches everything OFF.

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