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mswoboda avatar image
mswoboda asked

State of Charge of the Multiplus II is incorrect

I have a problem with the state of charge of the Multiplus II/VE.Bus.

If the battery (30kWh LiFePo4 self bulid with Chargery BMS and Active Balancer, configured as a 2 way signal BMS), is e.g. at a SOC of 20% and the sun starts shining, and the current is eg. 150A the state of charge jumps to 90%, but in reality (on the BMS) the SOC is 30%.


If then, the battery on this day didn't charge to 100%, the SOC is wrong. I.e. that overnight the battery is getting lower and lower. The VE.Bus system "think" its e.g. on 50% and is still de-charging, but the real battery state (BMS) is at 10%.
So the ESS setting which is e.g. at 30% has no effect.


SOCbatteryVE.Bus
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10 Answers
Kevin Windrem avatar image
Kevin Windrem answered ·

The other solution is to add a SmartShunt or other Victron BMS and feed that into the GX device via a VE.Direct cable. Then select that for the battery monitor in the menus. As others have said, any charging sources or loads other than the Multi(s)/Quatro(s) invalidates it's internal SOC calculations.

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mswoboda avatar image mswoboda commented ·

Thank you.
That would be an option to add a shunt. But then I have 2 shunts (one for the BMS and one for the Multis)...I am not sure if one shunt is adulterate the other...

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shaneyake avatar image shaneyake mswoboda commented ·
There is no problem with chaining shunts, only a very small Voltage drop for every shunt you add.
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mswoboda avatar image mswoboda shaneyake commented ·
Ah, good to know. Thank you.

So that would be really an option.


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marekp avatar image marekp shaneyake commented ·
If two systems use the same shunt resistance it is probably possible to use one shunt for both.

They will be just measuring voltage drop across one shunt.


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mswoboda avatar image mswoboda shaneyake commented ·

Yesterday, I installed the Victron Smart Shunt 500A and of course the VE.Bus has the right SOC now. Very good.


I cannot use the same shunt, because one is of the ChargeryBMS and the other one for the Victron system.

Unfortunately I cannot manage to program "Tobis hack" in the way that it will "send" the SOC to the Victron System...

Anyway its working now.

Thank you also for the info that adding a second shunt is not that problem (of course its not absolutely correct but I think is o.k.).


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nickdb answered ·

You need to make sure the multi is set to use the bms as the source for battery monitoring. Sounds like you still have the multis internal one enabled. Go read through the setup for supported batteries and you will get an idea of what needs to be enabled.

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mswoboda avatar image
mswoboda answered ·

The chargery BMS is not compatible with Victron. In the sense that they are "talking" (VE.Can) to each other. I know this.
Thats the reason why I have the "2 way signal" BMS.

Therfore in the setting of course is the battery set to "Multiplus on VE.Bus".

Generally "gueses" the Victron very good the SOC. But I dont understand, why its faulty, if the SOC is low, then is fast loading, and then it jumpes to 95%...

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mswoboda avatar image
mswoboda answered ·

I now try one thing, which could be the cause.

There is the DVCC setting "shared current sensor". It was deactivated, now I activated it.

Could it be, that if there is an increase in the current through the MPPT (because of sun) and the currents sensor is not shared, the VE.Bus system could think, that the battery is full, because there is so much current...
Hmm.. I dont know...


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Paul B avatar image
Paul B answered ·

There is a program that may interface the chargery BMS so it can become your BM

https://community.victronenergy.com/questions/57416/chargery-bms-on-venus-os.html

I have tried it on a site and it may help, if you can get it working.

the multiplus soc will go to 100% if the battery voltage reaches the absorption voltage - this could be because the battery cant take the full amp output of the multiplus - so try reducing the max charge amps under dvcc, otherwise more system information is required,

Ie some vrm voltage/amp and soc graphs would be of some help


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mswoboda avatar image
mswoboda answered ·

Thank you. I know the hack of Tobi already and have it implemented. But its not accepted by the VE.Bus System.
Its showing seperate the values of the battery cell.

If I choose it in the settings->system setup->battery monitor there are no values.

The script is a good idea, but not easy to run.
It works good for me to watch the battery cells from the remote console, but its not working in the sense of a VE.Can BMS (the script was never made for this).

I am sorry, that Victron doesnt support the script of Tobi and implement it in the VenusOS.
Maybe then its working for the purpose to use it as a battery monitor...

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mswoboda answered ·

Just a few details of my system.

Its a three phase system with three multiplus II /5000.
I have 15,8kWP with three MPPT VE.Can 250/100.
The battery as I said is a self build 560Ah, 29kWh. I have a seperate active balancer with 5A and the BMS is the Chargery.

Actually if the battery were charged by the multis everything is fine.
And the DVCC settings regarding the maximum Amp is only valid for the Multiplus.

If eg. the MPPTs are set to 90A (3x90=270A) and the sun is providing the energy, the MMPT are loading full, regardless of the DVCC setting (eg. 150Amps) in the Multis...I was always confused about this. But I tried all possible settings.


Unforunately I always have an error message if I want to insert an image (parsing response failed)...

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shaneyake avatar image
shaneyake answered ·

The victron equipment have know way of knowing what the SOC is.

You have to either have a BMS with Coms to the GX or a Victron Battery Monitor, IE. SmartShunt.
Without those 2 options the Victron equipment will never know the true SOC.
If your setup you can not use the built in battery monitor in the Multiplus.

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mswoboda avatar image
mswoboda answered ·

Hmm. If this is true, I have to program Tobis script, that I can use ChargeryBMS as my battery monitor...
Lets have a look...

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mswoboda avatar image mswoboda commented ·
I am struggeling with the script. I am not that good programmer....

There is another one form the user magpern, which should send the SOC to be vebus, but this is not working....for now....

Maybe I can mix it with the code of tobi...

That would be the smart solution.


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marekp avatar image
marekp answered ·

@mswoboda

When I was using MP-IIs for SOC measuring and my BMS would send to MP-II a signal "do not charge", SOC would be set to 90% regardless of the real SOC.

MP-II assumes that if battery tells it not to charge than battery must be full.

But there are other reasons for "do not charge" signal. Low or high battery temperature can also generate that signal.

Maybe you should make sure that the BMS is not sending to MP-II that signal for other reason than battery full.

That problem exists when ESS assistant is loaded.

"2 signal BMS" assistant can be set up so this problem is not present.

Installing SmartShunt fixed that problem.

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mswoboda avatar image mswoboda commented ·
Thank you.

Its not the BMS which send the signal, that the battery is full.

Its the fact, that the current originating from the MPPTs. So the Multis are not aware of that.

What I dont understand:
The MPPTs are connected via VE.Can to the Multis. Why are they not "talking" to each other.
If a MPPT is loading with eg. 50A, it could tell to the Multi, and its just substract it from the current which is coming/going to the battery.

I mean if discharging the Multis have the perfect SOC...

Yes, the shunt could be an option, if 2 shunts are working.

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marekp avatar image marekp mswoboda commented ·

@mswoboda

Double check if the "do not charge" signal is not sent by BMS.

This statement you made that (state of charge jumps to 90%) is exactly what was happening in my system when that signal was sent to MP-II by my BMS.

When you start charging battery in the morning it's temperature is rising and, depending on your setup, can go over the max temperature and BMS would send the signal "do not charge".

I found that problem in my system by replacing the BMS signals with jumpers for one day. Problem vanished.

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What is VE.Bus?