JK BMS 200A 24c, design flaw in SOC?

[SveinHa]

Hi all.

A few days ago, I fired up my new 48V LiFePO4 battery bank with 16 pcs EVE 230Ah cells and a 200 A, 24 cell JK BMS (version 2 with a start switch).

The BMS seems to work great doing balancing with almost zero configuration but the second day, I found that indication of SOC seemed to hang while the batteries were heavly discharged (60-80A). I also have a Victron SmartShunt 500 connected to the battery and it seemed to give e fairly correct SOC.

I contacted HankzorBMS Store and got a long reply saying, in short, that a sinus inverter load on the BMS most likely would give inaccurate SOC at best:

NOTICE: Protection (Current Sensor Anomaly) This problem exists when the inverter is used, because the current direction is uncertain, The alarm will be displayed. It does not affect the normal use of BMS. This kind of alarm will appear when the sun is not big or small, because at this time, the battery fluctuates frequently between charging and discharging, and there are uncertain factors, so this problem occurs. A pure sine wave inverter does not draw a constant current. The current from the battery follows a sine wave shape. It ramps from zero current up to peak current in 1/4 of a cycle. The peak current is actually about 40% more than the average current. Then the current will ramp back down to zero at the 1/2 cycle time. At this point, the inverter reverses polarity, and ramps the current back up again, hitting the peak at the 3/4 cycle time. The battery current is positive again, and the inversion happens in the inverter circuit. The the current ramps down back to zero again at the end of the cycle. The process them repeats for every cycle. If you measure with an averaging meter, you will just see a fairly steady current that should be close to the true RMS current. I use a True RMS Fluke meter, and it is able to give a vey accurate reading on this odd waveform. The current reading in the BMS just measures the voltage across a shunt resistor. This reading is only taken periodically, and it is not synced the the changing current from the inverter. It might take a reading at zero current, or at the peak current, but most likely, it will fall somewhere in between. Due to the shape of the wave, the reading tends to bounce a bit above and below the true RMS current. It is not perfect, but over the long term, it is "good enough" for the BMS to calculate the amp hours charged in or discharged out of the battery. This works because if you average the readings over a full hour, the high and low readings will average out. There is not a simple fix for the short te

In system log I find these messages:

Last reply from the store:

Sorry to bring you a bad experience. We will improve the design in the future. Thank you for your support

I've read quite a lot of good stuff about the JK BMS but in my head, a reliable SOC indication is a major feature of a BMS.

 

[ghostwriter66]

We ONLY use the Victron SmartShunt 500 out here for SOC ... I will say of all the BMS's that we have - and I think that we have tried them all -- virtually everyone of them is WHACK when it comes to SOC ... the Victron SmartShunt 500 is really the only one we trust ....

The BMS's work great - they just can't track usage well

 

[Steve_S]

Hi all.

A few days ago, I fired up my new 48V LiFePO4 battery bank with 16 pcs EVE 230Ah cells and a 200 A, 24 cell JK BMS (version 2 with a start switch).

The BMS seems to work great doing balancing with almost zero configuration but the second day, I found that indication of SOC seemed to hang while the batteries were heavly discharged (60-80A). I also have a Victron SmartShunt 500 connected to the battery and it seemed to give e fairly correct SOC.

I contacted HankzorBMS Store and got a long reply saying, in short, that a sinus inverter load on the BMS most likely would give inaccurate SOC at best:


In system log I find these messages:
View attachment 99077
Last reply from the store:


I've read quite a lot of good stuff about the JK BMS but in my head, a reliable SOC indication is a major feature of a BMS.

I had similar issues with two packs within my bank, after extensive troubleshooting the problem was resolved by "correcting" the Advanced Configuration resolving those issues along with a few others vanished.

Please refer to this post with the noted config changes.

My Final Config for Midnite Classic Solar Controller & JKBMS' w/ Large Bank (works amazingly well) Includes Charge Profile & BMS Config

INTRO: I have debated posting this for a while until I got everything tweaked in and working as best as possible. The End Result is Gobsmackingly Good ! I cannot speak for other SCC and such as each is different & unique in their own ways BUT this may likely be a Good Reference. Civility &...

diysolarforum.com

Hope it Heps, Good Luck.