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Does the BMS have to be connected to the inverter?

Wow, looks like I got there in the nick of time.

ZEVA said:
Important Notice: ZEVA products are going "open source"
-Ian Hooper, 6 August 2021

Last month I announced I would be winding down ZEVA in order to pursue other opportunities, with new orders accepted until the end of September 2021. After much community feedback and concern about ongoing availability of products, I have decided to "open source" the designs of all ZEVA products. This means that you will soon be able to download everything needed to reproduce each product, both pre-prepared production files and code/schematic/PCB files in case you wish to modify/add functionality.

All files will be provided freely to use for any purpose (including resale) and may be freely modified, but use is entirely at your own risk and without any support or warranty, including implied warranty of merchantability or fitness for a particular purpose.

Unless you're the sort of person who particularly enjoys the challenge of building new things, it probably won't be worth the time and effort of figuring out how to assemble each device yourself, but it is my hope that various individuals and businesses around the world will soon start reproducing the designs for resale in their region, and I plan to maintain a list of resellers on this website.

For the sake of a smooth transition, products will continue to be available here for the next couple of months, with 10% off all orders while stocks last. All products manufactured here will come with 12 months warranty and tech support. All product information, manuals and the contact form will continue to be available here indefinitely.
 
My notes with regards to current tapering are in line with a CC-only charge cycle with a balance phase (as short a CV as possible) and switch to a float. I can, however, see I didn't fully explain my point and I didn't word it correctly. Thanks @toms for pointing that out. Plus on my side, we've changed our parameters/targets over time and become a little more detailed about things as more lab testing has been done/published. Even different than some parameters/targets I have mentioned in the past.


This is what is interesting and can also be confusing to some people. I'm not meaning this towards you @GXMnow in any way, just commenting in general. Once we reach the voltage target, let's say 3.45VPC, and we hold that current, the current will begin to taper off until the charge termination parameters are met. This is very true! CC-CV charging.

However, by nature of the low IR of the cells and the low capacity of most balancing circuits, the current can at times still be too high for the balancer IMHO. This is not always the case if, for example, you're already charging at an extremely low current. The real key here though is that charge termination at target voltage will increase the usable capacity over the lifespan of the cells, hence the reason to taper charging to the absolute minimum while to balancing to termination. The longer one holds at the target voltage and continues with the constant voltage stage, the larger the solid electrolyte interphase (SEI) grows, thereby reducing the usable capacity of the cell.

Having high current balancers is extremely useful here because it helps to reduce the balancing time, thereby reducing the amount of time the cell is held at the target voltage.

Here are a few comments from a whitepaper discussing capacity degradation with PHEV and EV applications:

Source: Model-Based SEI Layer Growth and Capacity Fade Analysis for EV and PHEV Batteries and Drive Cycles

"Passive SEI layer growth is a major contributor to capacity fade in Li-ion batteries used for EV and PHEV applications. The majority of SEI layer growth will occur during charging. While fast charging creates undesired stress and temperature affects among other degradation problems, it will limit the amount of direct SEI layer growth in comparison to slow rates. Additionally, CC-CV charging will increase the amount of charge stored within a battery for a single cycle, but over the entire cycle life of the battery will decrease the total amount of usable energy from the battery for drive cycle cases."

View attachment 42776

Note that C2 results in the lowest SEI growth.

"Most charging applications apply a constant current charge followed by a constant voltage charge (CC-CV). While this protocol maximizes the amount of charge stored for a single cycle, the CV portion of charging greatly increases the charging time while adding stored charge at a diminishing rate. The increased charging time will lead to increased SEI growth. CV charging only occurs during the end of the charging cycle and at high levels of SOC. Figure 1 (above) shows that during the CV portion of charging the rate of SEI growth with respect to charge stored increases for all cases. Previous experimental studies have shown that increasing the portion of CV charging can lead to increased capacity fade. In cases where an EV owner is willing to forego the additional charge stored from CV charging (less than 10% in most cases), they will see a benefit over the life of the battery by reducing the SEI growth. Other degradation effects may negate the benefit of CC only charging."

So in many ways, switching to a float at the end of a CC cycle works well for retaining capacity. Hence my thoughts on reducing charging current during balancing to just enough to balance and then switching to a float, using a shunt to help ensure zero current flow into the batteries during float.

With a BMS without communication, here is what can happen with slightly mismatched cells. I'm NOT saying it does happen, I'm just saying IMHO we want to avoid it.

When we reach 55.2V in a 16S bank (3.45VPC target for example), we could begin constant voltage and the current will being to taper, if a person is using CC-CV. However, when we reach 55.2V, there is simply no way of knowing if all cells are at 3.45V or if any of them have exceeded 3.45V while yet being under the trip limit which is likely farther up into the curve (3.65V etc). Beyond that, most have a hysteresis beyond the trip limit (3.65V etc) so they don't trip in a passing spike. This is where it gets tricky IMHO.

IMHO we do not want to ever exceed 3.45V or whatever the target voltage may be. Essentially stay out of the curve as much as we can. We don't want cells exceeding the target and then waiting to come down while the balancer balances. We want to instead reduce current dynamically to a place where no single cell ever exceeds the target, keeping the incoming current low enough to allow the balancer to do its work.

One of the reasons for this to prevent the expansion of the cell as much as possible which can reduce the thickness of the SEI barrier and allow electrons to tunnel through the SEI barrier, breaking down the electrolyte. Expansion grows with the increase in cell voltage and SOC. This is where cell compression helps to reduce cell capacity reduction by reducing the amount of physical expansion.


I would recommend it. It's great for adjusting settings as time moves forward and perhaps we learn more about how to prevent cell capacity degradation. It's also the only way to see cell voltages. There isn't an app or wireless access.

I wouldn't recommend that style or model of contactor. I've heard too many bad things about those. I would look for a Gigavac ora TE/Sensata Kilovac. 100A is still good. I personally use 400A models from DC-Contactor.com. This one specifically.

I order factory direct but they maybe have them on aliexpress?

Here is one I found on a quick look:


Not the same brand and it's 500A. But that store looks like they may have others.
Hi Dear,whether i can apply this for solar charging? Thanks
 
Hello,


I am equipped with the Solis inverter RHI-6K-48ES-5G


I was using a BMS non bus can before with the profile "lead acid" of Solis with a battery LifePo4 "free" "no name "16S 280ah X2 or 560ah in total in 48V.


There was serious dysfunction of charge and discharge in these conditions.


The salesman indicates to me that it is because of my "free" battery with BMS npn bus CAN.

After about 6 months of troubles, I finally ordered a BMS CAN bus Seplos 100a card

After a few days of searching how to wire the control wires to the cells and make the USB/RS485 adapter key work on PC with the control software.


(quite complicated)


On the other hand, the communication between the Seplos BMS and the Solis inverter via CAN BUS was done instantly after connecting the Ethernet cable provided with the inverter !


Regards.
 
Hello,


I am equipped with the Solis inverter RHI-6K-48ES-5G


I was using a BMS non bus can before with the profile "lead acid" of Solis with a battery LifePo4 "free" "no name "16S 280ah X2 or 560ah in total in 48V.


There was serious dysfunction of charge and discharge in these conditions.


The salesman indicates to me that it is because of my "free" battery with BMS npn bus CAN.

After about 6 months of troubles, I finally ordered a BMS CAN bus Seplos 100a card

After a few days of searching how to wire the control wires to the cells and make the USB/RS485 adapter key work on PC with the control software.


(quite complicated)


On the other hand, the communication between the Seplos BMS and the Solis inverter via CAN BUS was done instantly after connecting the Ethernet cable provided with the inverter !


Regards.
Exactly which BMS did you use? Where did you buy it?
 
Wow, looks like I got there in the nick of time.
Good that you did.

I have the same Solis hybrid inverter as you (I think they are great for the price), but now I need to find a good set of 32 cells and a CANbus BMS instead of the ZEVA.
 
Exactly which BMS did you use? Where did you buy it?
Hello,
I use a BMS card (sold "naked" without box).
Model 100A 16s
Paid in total with rs485 adapter for PC monitoring software and fees and taxes, shipping about 230$.
(contact me vi MP for details)
Regrads.
 
Good that you did.

I have the same Solis hybrid inverter as you (I think they are great for the price), but now I need to find a good set of 32 cells and a CANbus BMS instead of the ZEVA.
The ZEVA does use CAN.
 
Hello,
I use a BMS card (sold "naked" without box).
Model 100A 16s
Paid in total with rs485 adapter for PC monitoring software and fees and taxes, shipping about 230$.
(contact me vi MP for details)
Regrads.
Hi, Can you tell me what 'battery select' profile you used on the Solis Inverter for this Seplos BMS please.
 
Opposing viewpoints here @the_colorist and @smoothJoey

Any more thoughts guys? I'm resigned to using the Overkill BMS and forgetting about canbus communication as it seems certain that the Solis won't support it from the Daly. And I can't afford the REC.

So the next step is 2 sets of 16s or 1 set of 16 x 2p.
If the inverter supports pylontech protocol over canbus, then the Seplos bms may be an option. They support Pylontech also
I have not tested it yet, but I have two on the way. They are 200amp, and seem to be an oem for other battery manufacturers. About $215 each last i checked.
I will know for sure in a month or so.
 
Hello! We built our own communication system between LiFePo4 batteries and MPP Solar inverter based on arduino. It monitors each cell separately and depending on the voltage of the cells controls the charging current until it stops if a cell exceeds the set threshold. At the same time, I put a modified firmware on the inverter so that it can receive commands from BMS without writing the commands in memory, these being limited. The system is called DLC, Dynamic Load Control. Demo (Romanian language):

else, data can be show on grafana: dlc.jpg
 
Bonjour, pouvez-vous me dire quel profil de "sélection de batterie" vous avez utilisé sur l'onduleur Solis pour ce Seplos BMS s'il vous plaît.
Hello, the bms seplos is connected via bus can and synchro OK (automatically recognized) via the battery profile ;
User defined
However, it seems that Solis will soon make changes that could make this profile disappear!
If this is the case, I say IF I could not use this BMS :(
To see in a few weeks...
 
Hi,

With the Solis in firmware version:
350025.F6

It is not fully compatible by going directly through the "PYLONTECH" brand mode of the Solis.

I have in my installation two BMS in series, one cuts the positive and the other the negative DC battery
It is necessary to make believe in the Solis a "fake":
- Set to "user defined" (bus-can), then "lead acid" and the it displays a fixed orange LED error and an error on the LCD of "bad no of the battery".

However it is the solution that I found to allow the simultaneous use of a non-communicating BMS and another bus-can.

Because otherwise in "user defined" mode the Solis makes you believe that you are setting the "bulk" voltage displayed;
However if you look in the "parameter editor" menu it displays another very high voltage as far as I am concerned; 57.6vdc instead of 54.8vdc (pack battery lfp 16s)

So the Solis applies the lead acid profile settings while allowing to have a double safety with the bms bus-can.
 
Hi,

With the Solis in firmware version:
350025.F6

It is not fully compatible by going directly through the "PYLONTECH" brand mode of the Solis.

I have in my installation two BMS in series, one cuts the positive and the other the negative DC battery
It is necessary to make believe in the Solis a "fake":
- Set to "user defined" (bus-can), then "lead acid" and the it displays a fixed orange LED error and an error on the LCD of "bad no of the battery".

However it is the solution that I found to allow the simultaneous use of a non-communicating BMS and another bus-can.

Because otherwise in "user defined" mode the Solis makes you believe that you are setting the "bulk" voltage displayed;
However if you look in the "parameter editor" menu it displays another very high voltage as far as I am concerned; 57.6vdc instead of 54.8vdc (pack battery lfp 16s)

So the Solis applies the lead acid profile settings while allowing to have a double safety with the bms bus-can.
So first you set "user-defined" then you set "lead-acid"?
Also, what voltages have you set for user-defined profile? I still haven't set mine properly.

I will look at the Seplos Battery Monitor software. It may be that there's a different profile pair that can be used instead of Pylon, like BYD.

Also, I'm going to write to Seplos and ask why their Pylontech profile causes fault on Solis inverter.

Merci.
 
So first you set "user-defined" then you set "lead-acid"?
Also, what voltages have you set for user-defined profile? I still haven't set mine properly.

I will look at the Seplos Battery Monitor software. It may be that there's a different profile pair that can be used instead of Pylon, like BYD.

Also, I'm going to write to Seplos and ask why their Pylontech profile causes fault on Solis inverter.

Merci.
Screens of my Solis, here:

And yes, step 1:
Battery:user definie
Step 2
Battery plomb acide

Normally is same on my Solis and BMS Seplos
 
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