Xiaoxiang BMS App Displaying Wrong Amp Hours

[TheWestern]

Hello all, first post and first LifePO4 battery build. I'm actually building to run an electric trolling motor, not for solar power, but you guys have all the good info so here I am.

I purchased a 200Ah LifePO4 battery set from Aliexpress, from a reputable seller with a lot of feedback. Also, a Xiaoxiang BMS to manage it. No problem setting it all up, but when I connected the app to the BMS, it displays, "19% charge, 13.14 V, 18.99 of 100Ah". Obviously this is 100Ah fewer than I expected, so: will the Ah update after charging or discharging? Or was I sent the wrong battery and I need to contact the seller?

Thank you.

 

[JRam]

Did you update the capacity in the settings of the app?

 

[GSXR1000]

13.12v doesn't seem charged... 100% is 13.6... 13.8

 

[TheWestern]

Did you update the capacity in the settings of the app?

Should I understand this to mean that the BMS does not automatically detect the Ah of the battery, and chose 100Ah arbitrarily, and I should input the real value with the assumption that the battery is 200Ah as advertised?

 

[JRam]

Should I understand this to mean that the BMS does not automatically detect the Ah of the battery, and chose 100Ah arbitrarily, and I should input the real value with the assumption that the battery is 200Ah as advertised?

Correct. The app doesn't know the capacity of the cells, once you give it the proper Ah in Base Parameters - Nominal Capacity then it will display as say 200Ah. The correct State of Charge should calibrate itself after charging/discharging a few times.

 

[TheWestern]

Correct. The app doesn't know the capacity of the cells, once you give it the proper Ah in Base Parameters - Nominal Capacity then it will display as say 200Ah. The correct State of Charge should calibrate itself after charging/discharging a few times.

Very helpful, thank you. Do you recommend discharging it through real use, or discharging using a charger?

 

[JRam]

Ideally you want to do a capacity test first to find the actual capacity of your cells. But if you skip this part it really doesn't take long for the BMS to show more accurate results. Any real life charge and discharge will get you there in no time. I would recommend doing a capacity test though, you never know what you get from Aliexpress.

 

[TheWestern]

Ideally you want to do a capacity test first to find the actual capacity of your cells. But if you skip this part it really doesn't take long for the BMS to show more accurate results. Any real life charge and discharge will get you there in no time. I would recommend doing a capacity test though, you never know what you get from Aliexpress.

Thank you. I see a setting in the BMS called "Total Cycle Capacity," it appears to be 80% of the amp hours (currently set 100000mAh and 80000mAh respectively). My assumption is that it is referring to how much of the capacity can be used before shut-down, and when I update configuration from 100 to 200Ah, I should update the total cycle capacity as well. Is that correct?

 

[JRam]

Yes, you got it, but that setting will not protect your batteries from over discharging. You can set those parameters under Protection.

 

[GSXR1000]

Yes, you got it, but that setting will not protect your batteries from over discharging. You can set those parameters under Protection.

agreed it won't stop discharging (or charging) til set voltages

 

[TheWestern]

Yes, you got it, but that setting will not protect your batteries from over discharging. You can set those parameters under Protection.

Thanks for your help. I have another question I'll ask here rather than start a new thread - My BMS was showing all cells balanced, as you can see above, then the next morning it was showing one cell at very low voltage - less than one volt. However, testing with a multimeter shows that all the cells are within normal parameters, about 3.27v each. I pulled the plug on the BMS then reconnected it, and it again showed that all the cells were normal, but within an hour was showing the same cell at extremely low voltage. I checked all my connections and they seem to be solid. Should I assume that the problem is in the BMS itself?

 

[JRam]

Thanks for your help. I have another question I'll ask here rather than start a new thread - My BMS was showing all cells balanced, as you can see above, then the next morning it was showing one cell at very low voltage - less than one volt. However, testing with a multimeter shows that all the cells are within normal parameters, about 3.27v each. I pulled the plug on the BMS then reconnected it, and it again showed that all the cells were normal, but within an hour was showing the same cell at extremely low voltage. I checked all my connections and they seem to be solid. Should I assume that the problem is in the BMS itself?

That is probably an issue with the wiring of the balance leads or the BMS itself. Check your crimped terminals, then see if the white JST connector at the BMS feels hot. Those JST crimps are a royal pain and can fail extremely easy, that is why they put a ton of white glue in them.

 

[TheWestern]

That is probably an issue with the wiring of the balance leads or the BMS itself. Check your crimped terminals, then see if the white JST connector at the BMS feels hot. Those JST crimps are a royal pain and can fail extremely easy, that is why they put a ton of white glue in them.

Good call JRam. I thought I'd checked all my terminals and double checked them, but sure enough, one was loose. Sometimes it's the simple things.