LiFiPO4 Batteries & Understanding BMS & App Readings

[LittleBear]

Hello... first post here but looking forward to getting to know you all!

I am wondering if there is a good resource which I can go to to learn about the BMS and App Readings which my new Lithium Ion batteries are generating. I have recently purchased 2 LiFiPO4 batteries, each with 8 cells totaling 24V and 10kW. The BMS on the batteries is JBD, and I am using either the OverKill Solar App (iOS) or the XiaoXiangBMS (iOS) or XiaoXiangElectric.

My problem here is trying to understand the readings which they are generating. I am attaching a screen shot from one of the batteries and using the XiaoXiangBMS. Note that all Apps read identical.



What I am trying to figure out is the SoC, and ultimately how long my batteries have to run my cabin. The App is showing the battery voltage as 26.67V which based upon SoC graphs online would suggest that this is almost 90% charged, yet the %age is reading 49%, which is the 197 / 400 Ah. Is there an easy rationale as to what the difference is? Is this battery actually fully charged? What do I need to do to get the battery fully charged?

Also, to complicate things even more, the following is the reading taken from the second battery, on a different date, but demonstrating the same problem I have:



Again using the voltage as an indication of SoC, this would suggest between 80% and 90%, yet the %age is again showing 49%, with the 281 / 640 Ah. The two batteries are identical yet they have different Ah readings. I have tried looking online for resources and material which can help me work through this but am not having any luck.

I appreciate this comprises several different issues but if someone can guide me to troubleshoot the initial one, then everything else may fall in to place.

A final question to you all would be which App do you find the best to use (I have iOS): Overkill Solar, XiaoxiangBMS or XiaoXiangElectric.

Thanks in advance for any pointers here and appreciate the feedback.

Stewart.

 

[Bob B]

There is a huge amount of confusion surrounding SOC with this BMS ..... Using the forum search will turn up MANY discussions.

Here is another from just this AM .... https://diysolarforum.com/threads/overkill-bms-useless.75849/page-4#post-971898 .... I generally use the XiaoxiangBMS app .... but have the others as backup in case it stops working for some reason.
The Overkill would be my 2nd choice .... and there are some very good documentation on the Overkill Solar web site.

 

[TacomaJoe]

The BMS on your second battery thinks it is 640Ah. That is a programable setting in the BMS and should probably be 400Ah. I use the Overkill app and at the bottom of the home screen is a tab to get to the settings screen. All sorts of numbers to review, with the capacity wrong, I'd check the other numbers to be sure that they are in the correct range.

 

[LittleBear]

There is a huge amount of confusion surrounding SOC with this BMS ..... Using the forum search will turn up MANY discussions.

Here is another from just this AM .... https://diysolarforum.com/threads/overkill-bms-useless.75849/page-4#post-971898 .... I generally use the XiaoxiangBMS app .... but have the others as backup in case it stops working for some reason.
The Overkill would be my 2nd choice .... and there are some very good documentation on the Overkill Solar web site.

Hi Bob. Thanks for the quick response. I did look at the other forums and I think the sheer number of other threads around BMS and Apps is what is throwing me into a spin lol.

So from your comment, the JBD BMS does not do SoC the same way as others would expect? Do the BMS automatically adjust SoC once it has gone through several cycles?

 

[Bob B]

Hi Bob. Thanks for the quick response. I did look at the other forums and I think the sheer number of other threads around BMS and Apps is what is throwing me into a spin lol.

So from your comment, the JBD BMS does not do SoC the same way as others would expect? Do the BMS automatically adjust SoC once it has gone through several cycles?

Initially, it will track the SOC based on the various voltage % settings.
It will track the SOC via coulomb counting .... amps in vs amps out .... and set to 100% once any cell reaches the "cell full voltage" setting.
If you write any setting change, it will temporarily track the SOC via the various voltage % settings til it reaches the cell full voltage again.

 

[LittleBear]

The BMS on your second battery thinks it is 640Ah. That is a programable setting in the BMS and should probably be 400Ah. I use the Overkill app and at the bottom of the home screen is a tab to get to the settings screen. All sorts of numbers to review, with the capacity wrong, I'd check the other numbers to be sure that they are in the correct range.

Thanks again for the quick response, TacomaJoe. Is there a set of "standard" settings/parameters which the BMS should be set to and I can cross-check at the same time as I go in to look at the Ah setting?

 

[TacomaJoe]

I don't know if there is a "standard" parameter setting list but here's what I have. Note that I have balancing OFF, I think the standard would be starting at 3400mV with a 15mV delta. I think most of the settings are pretty much the default except for the capacity voltages.

 

[LittleBear]

I don't know if there is a "standard" parameter setting list but here's what I have. Note that I have balancing OFF, I think the standard would be starting at 3400mV with a 15mV delta. I think most of the settings are pretty much the default except for the capacity voltages.
View attachment 187834View attachment 187835View attachment 187836View attachment 187837

Appreciate the screenshots. Will review against what the BMS provides and then likely will be back with more questions. Thanks for everyones assistance here!