question

David avatar image
David asked

ESS - DC Feed-in enabled, Charge Current Limit (CCL) from BMS ignored

There has been several posts over the years where users cannot seem to get DC Feed-in working correctly. The issue hasn't been restricted to a single battery type or BMS.

I use a Batrium BMS, however, others with Pylontech batteries have the same issue.

I spent the best part of a full day testing and reading about it and have come to the conclusion that when DC Feed-in is enabled, an important bug rears its head - and it's dangerous.

When DC Feed-in is enabled, and the battery is nearing top of charge, most BMS's reduce the Charge Current Limit (CCL) in steps to help avoid any single cell going over cut off voltages.

For example, let's consider a system capable of pushing 160 amps into a battery. As the battery starts to get close to the top of charge, the BMS may reduce CCL to 80amps, and steadily reduce this amount further as the battery gets closer to full. Eventually, the battery gets to 100% SOC and the charge current should stop - CCL = 0.

When DC Feed-in is enabled, the CCL is completely ignored. Only the Charge Voltage Limit is honoured. This creates big problems - and its dangerous.

So the system will pump as much current into the battery as it has available - regardless of the CCL value being sent by the BMS. While the battery SOC is low, this isn't a problem. When its close to full it causes big problems. The battery cells go over their limits and even when the BMS sends CCL of 0 the battery continues to be charged until the Charge Voltage Limit (CVL) is reached and the current naturally reduces.

There have been a few posts about this, but no one seems to have nailed what's going on.

Can someone else please confirm this.

Video Demo:

https://1drv.ms/v/s!AjZQHTTRHDNghodbXOaPiNx955NVPw?e=rSAZ6h


ESS
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Rob Duthie avatar image Rob Duthie commented ·
Hi

No issues here works very well with Pylontech battery.

Regards

Rob D

NZ

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David avatar image David Rob Duthie commented ·

Hi Rob.


Many people assume its working - However, can you take a look and confirm your DVCC is enabled, that DC Feed-in is enabled.

Then take a look at the current going into the batteries vs the CCL as reported in the Parameters section of your battery - See screenshot

ccl.png

Of course, this needs to be done while the battery is nearing full (but not) and while the sun is shining... Whats the current going into the batteries?

Can you confirm your MPPT models and the amount of solar etc?

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ccl.png (24.0 KiB)
Rob Duthie avatar image Rob Duthie David commented ·
Hi

Correct all enabled when the batteries are full and i have surplus power it's get diverted to the grid. from the charge controller.

As i know what the PV inverters are sending back, and then the MPPT is extra the power. I have seen it peak around over 7kW surplus.

I have a Smart MPPT 250v 60Amp Tr unit, Solar for the MPPT is 1890Watts.

The others i have 2x grid tied inverters on the input to the Multiplus2. 5 kw of PV

21kW of Pylontech batteries.

I will get more data when the sun is out next and the batteries are charged to 100%

Regards

Rob D

NZ

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David avatar image David Rob Duthie commented ·

The data when the battery is full isn't really all that useful. Please see this video:

https://1drv.ms/v/s!AjZQHTTRHDNghodbXOaPiNx955NVPw?e=rSAZ6h

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Rob Duthie avatar image Rob Duthie David commented ·
Hi


No it does not do that at all. the charge current backs of and is diverted to multiplus2 to export power to the grid.

Are you running the latest Venus software and multiplus softwares?

Regards

Rob D

NZ

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David avatar image David Rob Duthie commented ·

Yes, The Cerbo is running the latest beta, The Multi and MPPT's (x3) are all up to date. Here are some screen shots:victronfirmware.png

victronfirmware2.png

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victronfirmware2.png (27.2 KiB)
8 Answers
Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi @David

This is the reason that most batteries also reduce CVL when a cell gets too high, or even when the battery reaches 100% SOC


And even with only CCL control still it won't be dangerous, because a BMS will disconnect the battery if a cell reaches the maximum limit.


Also with a well sized system, this rarely is an issue except if for some reason DC PV power is way larger than inverter power. But than answer A and B come back.

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Daniël Boekel (Victron Energy Staff) avatar image Daniël Boekel (Victron Energy Staff) ♦♦ commented ·
PS. 100% charged should not mean CCL=0, if at target voltage (CVL) CCL=0, the battery will never be charged (without feed-in enabled)
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David avatar image David Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

Thanks - But you are ignoring the issue - If the battery is say 90% full and the BMS commands a reduced charge rate, with DC Feed-In being enabled, this is ignored? With DC Feed-in disabled, it works just fine.

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puitl avatar image
puitl answered ·

@Daniël Boekel (Victron Energy Staff) and @David
Hi!

Is there a solution for this problem now?

I have the same problem: CVL is working perfectly, CCL from BMS is ignored, also reducing charge current in the DVCC-menu doesn´t work.

What´s strange: Both thinks does work perfectly when charging from grid with the Multiplus.


My BMS from Seplos is sending a CCL of 10A when a (LFP) cell gets over 3,5V.
I think thats the perfect method because so the voltage of the higher cells just rises very slow and the BMS + my external balancer have time for equalizing the cells.
When reducing CVL the voltage of the higher cells also drops and so equalizing IS NOT possible.

@Daniel: Does it have a technical-reason that CCL only acts with Multiplus and when DC feed-IN is disabled or would it be possible and it "only" has to be add in you software??

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Daniël Boekel (Victron Energy Staff) avatar image Daniël Boekel (Victron Energy Staff) ♦♦ commented ·
Hi @Puitl

This has all been explained before. The technical reason is that it works this way to use all available PV power to feed-in to grid.

Battery / BMS design is not simple, but I can advise you to not charge above 3.5V per cell anyway. and set balancing to somewhere around that also.

If you look at the big players (BYD, Pylontech) they all send a higher CVL until the battery is getting almost fully charged, and than lower CVL. CCL is only lowered when a cell has overvoltage.

Note that balancing a battery should only have to be done once, after that only small corrections have to be made by the BMS.

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puitl avatar image puitl Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

Hi @Daniël Boekel (Victron Energy Staff)

Ok, i understand what you are saying.
I only charge my cells to 3,45V. Only once/twice a year i go up to 3,55V (slowly with keeping an eye on the cell-voltages) for clean balancing and "SOC-update" but nevertheless two points:

1) I am sad about it that reducing max. charge-current in the DVCC-menü does not act!
(I have 10kWp and 3x MP2 3000 and with max. charge-current i can stretch battery-loading troughout the day - now i have to do it with turning up and down the CVL, which is not very smart ;)

2) When there is no technical reason and "our problem" is solvable with a simply programm-update from you, i don´t understand why you not do that because with this feature you don´t make any mistake, go up with the "philosophy" of other BMS beside Batrium and at the end you would add a additional feature to protect our expensive cells from overvoltage.

So please adjust this point :) :) :)

With 10kWp and 14kWh battery I do not care if there are flowing a couple of watts into the grid instead of the battery ;)


Thank you - I remain in joyfull anticipation :)

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Daniël Boekel (Victron Energy Staff) avatar image Daniël Boekel (Victron Energy Staff) ♦♦ puitl commented ·

@Puitl the technical reason has been explained a long time ago. feed-in means we need MPPT's to produce, it is not possible to combine this with a low charge current on the batteries because this would open a world of pain with oscillating systems.


Remember that most setpoints in the system are voltage based.


This all works perfectly fine with approved batteries

We support self made batteries as you know, we help you with tips and hints on how to properly configure them to work well. What more can we do?

I'll advice you once again to read my advice, look at how commercial batteries work (as I explained in this thread), and adjust your BMS settings accordingly.

PS. how is the Seplos performing? I have a couple of them I want to try out with personally but didn't have time to play with them yet.

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puitl avatar image puitl Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

@Daniël Boekel (Victron Energy Staff)

"...it is not possible to combine this with a low charge current on the batteries because this would open a world of pain with oscillating systems. "

Thank you, exactly that is the technical-explanation which I have been missing so far!
Ok then you have to correct this part in your Cerbo-GX manual...

ccl-cerbo-gx-manual.jpg

...into "CCL and limit charge current does only act when charging from grid with Mulitplus"!

To the Seplos BMS:
I like it much. Price/Feature/Performance-ratio is excellent.
All important parameters can be adjust with the software. With the software you also can watch "live" to the battery and single cell voltages and can record an live-view which can be exported as an Excel-file with all data.
(For example to look which cell is the weakest when discharging to SOC 0% without the need to "wait" live on the System and have a look every second).

SOC-calculation seems also very exact.

The only problem is that the Seplos only reduces CCL when cells go over 3,5V (adjustable), but i think you know that by now :D

I will write Seplos to think about to also adjust the CVL....

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ccl-cerbo-gx-manual.jpg (52.8 KiB)
Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ puitl commented ·

There is an additional note in the GX manual under the section - 8.6. DVCC for systems with the ESS Assistant -

  • Note: When 'DC-coupled PV feed-in excess' is enabled with ESS, the DVCC system will not apply the DVCC charge current limit from PV to battery. This is behaviour is necessary to allow the export. Charge voltage limits will still apply.

    Charge current limits set at the individual solar charger device settings level will also still apply.

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puitl avatar image puitl Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

@Daniël Boekel (Victron Energy Staff)

Question: Why does it work with BYD-batteries??
See this forum-entry and the 3 after it from me and user "optip":
https://www.boards.ie/discussion/comment/118798364/#Comment_118798364

At "optip"´s BYD-system CCL will be transfered into the MPPT / Networked Operation settings, at my system it doesn´t although the reduced CCL is visible in the BMS-parameters in the remote console!?


Please help me, i don´t understand it (:

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Daniël Boekel (Victron Energy Staff) avatar image Daniël Boekel (Victron Energy Staff) ♦♦ puitl commented ·

the Victron system works the same with BYD, BYD lowers CVL when battery full. But if you take a small BYD battery and big MPPT's, combined with too little feed-in capacity, it will also charge more current than asked.

But with every system: if CVL is reached, it won't go higher.

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puitl avatar image puitl Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

I texted Seplos, we will see if they update the software to also beeing able reduce CVL...

I think the following is simple and would help:
(BMS standard CVL is 56,8V = 3,55V per cell)
If single cell gets over 3,55V then reduce CVL at 0,5V
If single cell gets over 3,60V then reduce CVL at 1V

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custom avatar image custom puitl commented ·

Is there a way to automatically adjust the CVL in Cerbo with a defined offset when a CCL is active? Then nothing would have to be changed in the BMS.

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custom avatar image custom custom commented ·
Like the Quirks for some BMS in the dvcc.py file.
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puitl avatar image puitl custom commented ·
I think there is a way, but only in a "custom way" ;)

My suggestion above is easy to update to the BMS and Seplos will think about it.

The problem with reducing CVL when CCL is active:
Seplos standard CVL is on 56,8V = 3,55V per cell.
When cell gets over 3,5V CCL = 10A to give the balancer time for balancing.
When you go down with CVL at this point your cells will not be "fully" charged (you are loosing about 0,x% capacity) because you are reducing the absorption-voltage.

For me my it is better to see it as a "protection":
When one cell gets over it´s charge-limit (3,55V) then reduce CVL more and more and set it back when cell gets under 3,55V, so when they are in top-balance all cells have 3,55V = 56,8V and no CVL-reduction is needed.
If that´s not enough then you have big disbalance and BMS cut-off would be active.

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custom avatar image custom puitl commented ·

ok, then it makes more sense if the BMS lowers the CVL when a cell reaches the limit and the CCL continues to be ignored.

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Andy avatar image Andy puitl commented ·

The Seplos BMS can reduce the current itself on the hardware site of the BMS. It also sends the CCL to the Venus OS but is not reliant on what comes from the MPPTs.
This feature is absolutely overrated and more marketing from the Seplos side as anything useful.
Reducing the current to 10A to allow the balancer to do its work, is not working at all. The Seplos balancer does 150mA at its best! You effectively reduce the charging current from 10A to 9.85A for a cell which is already at 3.5V. This will not stop it from going up further and eventually trigger the OVP of the BMS.

At the beginning, I also thought the CCL to 10A limit is a great feature but it's not useful with LFP batteries due to the flat charging curve. Once a cell hits 3.5V, you need to stop charging altogether or OVP will kick in quickly afterwards and disconnect your battery. It may work better with Li-ion cells and a more linear charge/SOC curve.

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puitl avatar image puitl Daniël Boekel (Victron Energy Staff) ♦♦ commented ·
@Daniël Boekel (Victron Energy Staff)

Short question: When the CCL from the BMS is 100A and i have installed two MPPT´s 250/100 which can reach 200A charge-current: Does the System charge with 200A or does it react to the BMS and only charge with 100A?

If 100A:
- Does the MPPT´s reduce the Power so that only 100A go into the battery
OR
- MPPT´s = full power and the Multiplus try to get the power into the grid so that da charge-current is max. 100A (with problems of too slow power regulation so that the charge current could be more than 100A for short time
(What´s happening when the power of the Multplus is too low to get all neccesarry power into the grid?)

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nickdb avatar image nickdb ♦♦ puitl commented ·
DVCC restricts the total charge, across all devices to the CCL of the BMS. The chargers will all throttle back unless there are AC loads to supply. The clue is in the name - Distributed Voltage and current control.
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Daniël Boekel (Victron Energy Staff) avatar image Daniël Boekel (Victron Energy Staff) ♦♦ puitl commented ·
Hi @Puitl as explained, if feed in DC is enabled, it will charge full power because the inverters have to feed in to grid.


size your system correctly if this could be an issue, if your battery is big enough normally there is no problem.

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pekoc avatar image pekoc Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

I don't like this assumption. If the battery is cold, it doesn't matter what size it is, the max chaging current is asked to be reduced to not damage it. But you say we are exporting to the grid when the battery gets full, so we don't care the battery is cold and pushing the full power into it. Also when the battery is full and the CCL is 0A, you override the BMS logic and still charge the battery because CVL hasn't been reached. I've got the BMZ ESS Z battery which normally reports CCL 82A, when full it reports 0A, when it is at 20%, the CCL is 54,5A. When the battery temperature was at 6°C, which is the lowest it got so far, and the SoC was 40% the CCL value was 63,9A etc. My PV panels with MPPTs are able to provide 130A at full sunshine if the battery is at lower voltage around 50V, so even if I double the battery capacity, it would not be enough for low SoC limits.

Currently multipluses are able to adjust their power based on the load on the output. Why isn't it possible to adjust it within the limits the same way as when DC feed-in is switched off? Of course the measurement delays makes it harder to adjust correctly and there is some chance it will start oscillating, but the regulation for sudden load change does not react immediately either so I assume the same way could be used to stay within the limits reported by BMS.

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baxter avatar image baxter pekoc commented ·
Discussing this topic with Victron was like talking to a stonewall.


It is not a bug, it is a feature :)

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pedaaa avatar image pedaaa baxter commented ·

it really would be a nice feature if Victron would made it "configurable"


so to speak:

if selecting DC-Feed-in, let a 2nd parameter pop up "ignore BMS-CCL Yes/No"

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stefan1967 avatar image stefan1967 pedaaa commented ·
Yes, that would be also my prefered solution.
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larsea-dk avatar image larsea-dk baxter commented ·
Sad to hear. Any NodeRed possibilities??
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stefan1967 avatar image stefan1967 larsea-dk commented ·
I created a small node red script and set the grid value based on calculation, it works but I would prefer a build in solution. Becaus what happens if grid is switched off for example, the grid set point is not possibel anymore and I asume the mppts are still pumping their full load into battery.
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puitl avatar image puitl pekoc commented ·

@pekoc

Victron say that their system is "voltage-leaded", they can´t regulate to a desired CCL additionally - i don´t know if it is only "a little bit difficult (because of oscillating) or if it is complete unpossible".

So it is important that your BMS lowers down the CVL when a single cell-voltage is getting too high.
They recommend the REC-BMS, but also this one goes at first down with CCL and if it don´t work also with CVL (almost as a failsafe).

Victron-Statement: For all other situations you have to size your system (= the MPPT´s) so high that the battery can manage their charge-current anytime...


In the end i still don´t understand it because:
- The Multiplus can handle a max. grid feed-in power
- The MPPT´s are able to reduce their power

(I think it is still possible, but hard to implement to have a "soft regulation" at the end)

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larsea-dk avatar image larsea-dk puitl commented ·

I have tested a bit, when the battery is charged fully to CVL, infeed will start. I only have 1 MP2 48/5000 but 2pcs MPPT 250/100. If I lower/limit the feedin power, the MPPTs are also lowering the power from the MPPTs. So they respect CVL+ the 0.1volt or so. So you dont need to have inverter power larger than you MPPTs. But maybe it will be smart, I dont know.

But since I have 2pcs MPPT 250/100 I also really need a way to lower the charge level CCL somehow! 200A potentially is way to much and also not in any way necessary.

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puitl avatar image puitl larsea-dk commented ·

Mybe you can handle it with the new integrated NoteRed:

"If CCL get´s too high then increase (actually "decrease") grid-setpoint...or decrease CVL"

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larsea-dk avatar image larsea-dk puitl commented ·

Im not strong with NodeRed….yet.

Could it be possible to by nodered to set mppt max charge to i.e. 35A every night, so this will be the max battery PV charge. And when CVL is reached(charged battery), the mppt were set to full charge capacity to feed in max energy?

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larsea-dk avatar image larsea-dk puitl commented ·

Might be a good idea. any experience with that.

If I lower the CVL, what is the charge current then? For me it seems like jumping from full throttle to very low charge current. Where to get or see data on how MPPTs work?

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schaka avatar image
schaka answered ·

Hello, i had the same problem with my ESS System. Acutal Firmware is v2.84 on my cerbo.
I use 3x Multiplus II 48/5000, Cerbo GX, 3x MPPT 250/100 with 15,3 kWp Solar Moduls (45x Sunrise Energy 340 Wp). I use one BYD LVL 15.4 Batterie. Max feed in from energy provider is 10,7 KW.

If the batterie SOC is at 100 % and the generator power is very high, the batterie is always a little bit "overload". The bms sent error messages to my cerbo, and i have many days a report in the log.

I think the cerbo/multis need to regulate the mppts if the batterie is full.
Is there any option to use it normaly? Is there a change Victron is fixing this "control" problem?

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puitl avatar image puitl commented ·
What is the CVL from the Battery and what is the max. voltage the battery reaches in this case?

You have to take into account that the MPPT´s charging-voltage is 0,4V higher than the CVL when Grid feed-in is active (it´s neccessary so that they can power into the grid).

Mybe this is enough for an alarm from your BYD...but then other people should have this error too.
You can activate DVCC in de Remot Panel and then reduce the max. charging voltage slightly...

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stefan1967 avatar image
stefan1967 answered ·

Same problem for me - much too high current to battery in DC feed on. I creted a workaround with node red, setting grid point. But i would prefer a build in solution from victron.

if selecting DC-Feed-in, let a 2nd parameter pop up "ignore BMS-CCL Yes/No"

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tranzorb avatar image
tranzorb answered ·

@Stefan1967


Hi,

I have the same issue with my system, by any chance could you post somewhere your node red flow?

Thx

Fred


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2bbionic avatar image
2bbionic answered ·

Same issue here - ramping of my battery CC is ignored as soon as I activate Feed-In.
I also would prefer an solutions like proposed from @Stefan1967 but in the meantime - is it posible to get you NodeRed flow?


Regards,


2bbionic

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ecotechcanarias avatar image
ecotechcanarias answered ·

I have the same problem with a multiplus II 5kVA and a REC BMS. I have replaced the BMS 3 times.


The CCL reduces to 0A, but the battery continues to charge with little current 0-2A.

This is a big disaster. All the LFP cells charges over 4V !!!


1695837782194.png



1695837782194.png (477.1 KiB)
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puitl avatar image puitl commented ·
It´s not possible to make your picture bigger to see more...but why does your REC go up your cells to 4V!!??
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grua avatar image grua commented ·

Is the CVL transmitted from the BMS to the Victron? If so, then I think the problem is that the BMS doesn't lower the CVL?

With my BMS (communicating with Cerbo via CAN) the CVL is reduced when the battery is full, but with yours it even increases to 62.7V?


And shouldn't the BMS switch off long ago with such high voltage?

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puitl avatar image puitl grua commented ·
@grua which BMS do you use?
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grua avatar image grua puitl commented ·

It's a 14,3 kWh baterry from Gobel Power, BMS 150A.

Some say, the manufacturer of the BMS is Refinergy. I'm not sure...

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lm-31 avatar image
lm-31 answered ·

Hi, is there any further solution to take CCL into account, in the case where grid feed-in is enabled?

It's quite annoying that the Multiplus can handle a lot of differents functions, but not this one which doesn't seem that complicated (and besides is linked to security) ...

For those who tried something with Node Red, is it working well / difficult to configure?

I begin to understand well ESS, but not a clue aout Node Red.

Thanks :)

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