A PV supported by a SolarEdge inverter SE10k, with 10kW in solar panels;
Two sets of 16kW LifePo4 cascaded batteries that have their own BMS;
One MPPT SmartSolar 250/60 (to be installed).
Because I will have a MPPT, I have enabled DVCC as the BMS can properly send CVL, CCL and DCL.
However, the BMS does not report a precise SoC so I am willing to install a SmartShunt.
My question is:
Since the BMS will still be in control of managing the batteries (limiting current, handling protection, etc.), will the SmartShunt be able to report a reliable SoC? And what are the possible side effects or limitations of this mixed setup?
I have a BMS and a SmartShunt because I do not trust the BMS SoC.
Multiple battery monitors in the system are not a problem, and they all get logged in VRM.
But only one can be used to control charging.
In my case, I’m doing the opposite of what you want. I use the SmartShunt to control absorption and float voltages for the system. I use the BMS info only to monitor the state, “No BMS Control” is set. Alarms from the BMS still get logged and sent as notifications, however.
Actually, that was my doubt: why rely on the BMS if I can tailor the charge limits and have it done by SmartShunt? I guess your approach is much better and that, if something goes wrong, the BMS should protect the batteries. But take a look:
So, for a long period of time the battery was not getting any power, announcing a 100% SoC and a CCL of 0. However, during the time you see it at 100%, it was doing the balance of the cells. As you can see, the voltage dropped from 56V to less than 53V. Also notice that the BMS has set CCL to 0.
With this in mind, what I am not sure is if I should just “don’t care” about this CCL of 0 and let the SmartShunt do its job.
Regardless of what you do, the BMS over-voltage, under-voltage, and short circuit protection protect the battery, so no issues there.
When the battery hits 100%, do you get a cell over-voltage warning?
My batteries stop balancing when this occurs, yours may have different behavior.
The voltage sloping down during that time could be simple relaxation of the voltage because the BMS may have disconnected the charging FETs.
Are you sure the balancing is happening?
Do a comparison of the BMS voltage to your inverter or busbar voltage.
If the difference is large, and no current is flowing, the BMS is reporting the internal
battery voltage and not what is at the terminals (mine does that, yours may not).
Your BMS sets CCL to zero to tell the system to stop charging.
Other BMS lower CVL instead. I’m guessing that the charging FETs are also disconnected.
If you let the smartShunt controlthe system, you will need to pick absorption and float voltages that make sense for your battery. I recommend starting at 55.2V, and gradually increase it until you are satisfied that you are at 100% SoC.
Also, note that if the SmartShunt is the battery monitor, DVCC max voltage limit (if you are using it), will be ignored. It only applies when BMS is in control. This is not obvious.
Yes. Most of the time I get a message of over-voltage. Then CCL is set to 0 and it starts balancing. I am sure about this because I can see the BMS via their own software.
And yes, I have enabled DVCC because I will have a MPPT. I red somewhere that this is the way you can inform the MPPT what is the voltage it has to produce.
I will take your approach! It is always a learning process. So, if you allow me I would like to ask you some few questions:
What kind of batteries you have, lithium or lifepo4?
The sets of charging will be done at VE Config (on Multiplus) or in SmartShunt?
What else (parameters) would you suggest as a good start point?
You can do it either way once you have the SmartShunt.
I have 3x EG4 rackmount server batteries (51.2v nominal) LiFePO4
You should set both the multiplus voltages and the SmartShunt voltages.
I use 55.2V absorption and 54.0 V float (which is very conservative).
This is the level at which I do not get any over-voltage warnings.
If I wanted to get that extra 1-2% out of the battery, I would increase the absorption in 0.1v increments until the warnings returned, then back it down.
Take a look at diysolarforum.com, lots of non-Victron and Victron battery discussions there.
Tomorrow I will have a real sunny day. I have changed my sets as discussed so far. If I get something strange, I can discuss here. If everything goes as expected, I will close it.
Hi
Are you sure. I have understood it otherwise
I have my battery monitor set to the Smartshunt and under DVCC I have set controlling BMS to the BMS.
I have heard that, if you set the Smartshunt as controller, then no CVL, DCL etc is not provided by the Smartshunt since it cannot give you these informations. So if another unit is connected like the BMS, the reported CVL etc. from this BMS will always be used. As I understand, the Victron will always find the lowest value set in the system with regards to CVL, DCL etc even if you just have set a hardlimit in the Remote Console.
Do note, that with Feedin active due to ESS active will remove the CCL limit towards limiting the MPPT’s, since it is expected that excess is feed in. I’m not sure if Victron managed to control CCL on the battery with the new VenusOS. In the past (with older VenusOS) I found it charging quite intense near a high SOC, so I did a Nodered code that tweaked the Gridsetpoint, to lower the CC at higher SOC. Any experience??
I am actually using the dbus serialbattery driver to transfer BMS values to my Victron system…also with the benefit og tracking it and see it online in the VRM.
It is quite complicated. I noticed that the BMS sets the CCL to zero while it is balancing the cells and, when it starts balancing, they are not yet at the full charge voltage.
Now, if I impose charging via SmartShunt (if I just don’t care about the BMS) I don’t know if they will get ever balanced. Also, the BMS has a MOS control (see picture below) that I don’t know if it will automatically turn off charging even if I force it via SmartShunt.
I don’t have yet the SmartShunt, I just ordered it. I guess I will only find the right way to go once I get it and do some tests.
Regarding to the MPPT, this is really a big question I have as I must have ESS active. Now, if I limit the feed-in via ESS will the MPPT reduce its production when the batteries are charged? I always thought that this is the main function of DVCC that is distributing the information about the battery state, voltages, etc., so all the system components can adjust accordingly.
Perfect! I will go for that and keep learning and giving some feedbacks.
Now, due to several questions I had because the wrong SOC, the BasenGreen support services has asked me to: “Discharge the voltage of the battery packs below the undervoltage protection, and then charge to the battery pack overvoltage protection.”
And yes, they put it in “bold”… The undervoltage protection on their BMS starts at 43.2V, so 2.7V at cell level. Look at the pic below.
But, where can I set such voltage as the minimum SOC level? While using the BMS only, I have set the minimum SOC to 0%. Still the DC would never go below 49.8V and would enter into “Sustain” mode.
