SG48100p batteries SOC inconsistent with battery voltage

[Stan7x]

Hello, recently I built my system based on two Sungold SP6548 inverters and 8x SG48100p batteries. I set it for test with just 4x 450watt panels connected to one of the inverters ( in series). For a month the system ran fine, charging all eight batteries with BMS communicating in PYL mode (at least what I thought by just looking at led lights on batterie's front panels) . I was not using much power, just ran the countertop oven from it from time to time, just to test it. One day it started throwing error 71 and stopped producing electricity. At the same time, all the batteries showed 4-5 lights SOC on their front panels. Upon checking individual cell voltages of batteries that went into alarm it became evident that some of the cell voltages fell below 2.7v and pack voltage was something like 43v. At the same time, SOC was showing more than 90%.

I shut down all the batteries and started charging them one by one from the inverters. I charged two batteries so far and found that battery voltages are inconsistent with their SOC. For example, first battery shows 53.42V with soc of 94.91% and second battery shows 52.79V with 98.96% SOC! Is there a way to balance the batteries so that their voltages are consistent with their SOC? I understand the logic of BMS is that it tracks SOC and once it reaches 100% charging stops. It does not matter that cell voltages are 2.7v and pack voltage is just 43v, if it tells SOC is 100%, you cannot charge it more. It takes one of the cell's voltages to drop below 2.7v and battery goes into alarm and disconnects having SOC value of more than 90% at the same time. How would you advice to go about that issue?

 

[marionw]

The batteries have not been charged to where cells start to balance.

Download the SOKTool software from Current Connected. Using an RS232 to USB Converter cable plugged into a computer (and the RS232 port, center small RJ12 jack on the battery) you can monitor the battery to determine if/when cells start to balance. When cell balancing starts the BMS will reset the SOC to 100%. If you have one or more cells that reach Cell Overvoltage Protection resulting in the BMS turning off the Charging MOSFETS (thus stopping the charge) before cell balancing then the BMS may not reset SOC.

SOKTool software; last link on page.

SK48V100 Server Rack Battery Owner & Operator's Manual | Current Connected

Full instruction manual for the SOK SK48V100 server rack battery. Everything you need to know is contained within this document!

www.currentconnected.com

This is the RS323 cable I use:

Amazon.com

 

[Zivva]

You need to confirm there is actual communication between inverter & batteries : to be checked on your inverter, there should be a menu displaying this information.

If there is no communication & charging voltage is too low, batteries can't get charged to 100% then BMS won't calculate SOC properly ... With some huge deviations after a while as you witness.

This is a Pace BMS : it sets SOC @ 100% once 1 cell or the full pack reaches OV alarm : 3.60V, 54V (15S) or 57.6V (16S) default settings.

By the name of your batteries (48100), I would assume those are 48V / 15S. Then charging voltage should be set to 54V to reach OV alarm and giving time for cells to balance. After a few cycles and cells getting more balanced, you could decrease charging voltage to a more reasonable 52V or less ...

 

[Stan7x]

These 48v batteries have 16 cells, so I guess they are 16s. According to the manual hey have 57.6v cut-off voltage for charging and recommended charging voltage of 54.5V with discharge cut-off voltage of 43.2v. It sounds like I have to try to charge each battery with something like 58v according to multiple threads on this forum, mostly about EG4 batteries. The problem is that once perceived (by BMS) SOC hits 100%, charging stops, no matter that the pack voltage is actually below 53V. I am just looking in the menu of the battery itself, not the one on the inverter. Inverter seems to communicate with the battery fine in PYL mode while charging. The battery icon is constantly flashing in the invertor menu when I set PYL protocol for battery-invertor communication. I wonder how to by-pass BMS and let the voltage of the battery go above 53V. On the first battery I was able to do that by discharging the battery first to 0 (with voltage dropping to something like 41-42V ) . At that point SOC abruptly hit 0% and charging became possible to above 53v. I was not able to do that with the second battery from my start post, but not with first one and I have six more batteries to go!

I will by the rs232 cable and try to install SOKTool. What can I see in SOKTool of what I cannot see in the battery menu?

 

[Zivva]

By charging @ 58V / 3.625V per cell you will inevitably get 1 cell hitting OV alarm when others maybe well < 3.4V, charging stops as soon as 1 cell hits OV (could be as low as 53V ...) creating more unbalance ...

Would charge lower than that, max 57.6V or bellow (56V minimum) to leave time for the running cells to balance & get the lowest closer to 3.4V.

The BMS software gives you the same info you get from the screen + you can record pack / cells voltage instead of spending your time looking at the screen to determine what is the issue.

+ You can change some settings if needed as batteries assemblers have a tendency to set either very agressive or too conservative settings.

 

[marionw]

Lots of good and informative stuff.

As the cells start to balance you will see "Bal" beside the cell.

Use "FF" for the Pack in the "Serial Port" box before opening the port so you can see all batteries.

paceadmin is the password

 

[Stan7x]

Ok, an update to my struggle with BMS reporting bogus SOC. I tried to charge the battery to higher voltage to no avail because once again, SOC hits 100% - charging stops. I had a battery in my pack with SOC of 94% and voltage of 43.6v. With this voltage, the battery should have almost zero SOC. I read several threads on this forum with people struggling with the same problem, mostly with EG4 batteries, for example here or here. There was no real solution figured out in these threads except updating the battery's firmware, which for Sungold batteries is not an option. One of the guys there went to such an extreme as to opening up the battery and charging individual cells to 3.5v with a bench charger. I was definitely not willing to do that.

I decided to go the other way - instead of charging, I started discharging the battery. I switched program 5 of the invertor to USE and set DC limit cut-off in program 29 to 42v. After that I turned on the inverter, connected it to just one battery and disconnected PV array from the inverter. These Sungold inverters have about 87 watts of idle consumption, so this already drained battery started draining quickly just on idle invertor consumption. I was watching individual cell voltages which were a little bit above 2.7v initially. Once one of the cell's voltages went below 2.7v, battery started flashing alarm red led. Once the voltage of one of the cells hit 2.5v, the battery turned off itself, but at the same time, SOC instantaneously dropped from 94% to 0%, which was my goal!

I turned on PV array to try start charging the battery back, but invertor refused to charge completely drained battery. I guess with a bench charger I would have been able to charge it, but invertor is too smart, it does not charge if it senses the voltage is too low on the battery. So I turned on another battery in my pack and it charged that drained battery a little bit for the cell voltage to go above 2.6v and to start the battery. Once the battery started, I began charging it from the invertor using PV array still in user mode. I did try to to switch to PYL mode, but invertor started beeping and throwing that dreaded error 71. So far I was able to charge that battery to 70% soc and 53.345V voltage.

The bottom line - SOC resets to 0% once one of the cell's voltages hits 2.5v. Overall conclusion is that this BMS is engineered really badly, a normal user should never jump through hoops lake this. This bad BMS design is not unique to just Sungold, but perhaps pertains to other batteries such as EG4, SOK, etc. Apparently SOC is based on Coulomb counter by just counting ampere-hours. Once you pushed 100 A-h through the battery, SOC is declared 100% without any regard to battery's voltage.