Wrong SOC on V15 and V19 JK BMS

[GlenB]

Hello,
I have three DIY packs, EVE LFP 304 or 314aH. I have a mix of V15 and V19 bms. V19 has .02 firmware, V15 has the last one issued (.41?).
My inverters have shut down before dawn quite a few times, with them all reading zero percent or nearly zero. I go out to the power shack
and see that the voltage is 50.4V. No where near zero percent!
I go through my exercise of going into BT and resetting the SOC by changing the pack capacity by one: from 304 to 303aH.
This sets the SOC back to some sane value. In this case of 50.4V, it came back to around 30%.

Can any tell me what I have done wrong in the settings to cause this to happen? I use Andy's OffGridGarage settings...

Should I upgrade the firmware on the V19 master?

BTW, I hate having to go outside and use BT to change the bms settings. I have ordered a couple EW11 modules to use WiFi to RS485 so I can use the PC program
to monitor and change the bms's.

 

[Sparkyaz]

What is your inverter set to shut down at? 50v is kinda high for a cut off, But if there is an appliance kicking on, it could trip a low voltage shut off.

The next question would he how are you getting SOC? Thru the inverter of individually pack by pack?

If you’re still able to use BT to connect, that tells me power isn’t totally lost.

And if your having power issues, I’s steer clear of using wifi for your data

. But truly, more info is needed. Hard to tell what exactly is shutting the system down.

Is this a new issue, or has it been an issue the whole time.

If it’s new, what happened around that time frame?

Also, keep in mind- when you are seeing 50v, that is a static no load reading. What was the reading when it shut down? I assume that is currently an unknown number.

And until you catch it in the act, it will be a guessing game.

 

[GlenB]

Inverter set to 20%, but it does not work. It is the bms that shuts off, removing battery from the inverter. I have the appropriate lcd modules with the bms modules. The master V19 show the overall group status (900+ amp hours and I guess average voltage and SOC for all the packs). Never seen it shut down, and still be at 20% on the bms lcd.

You are correct, the bms display says zero percent, but there is lots of voltage to power the bms. I have not confirmed it, but I suspect the output is turned off. I have had a bad cell before, and it shut down, because one cell hit the min voltage of 2.65v. All the rest of the cells were at 3.15v

This has been happening with only V15 bms and now with multiple bms with V19. It might have worked long ago with just ONE V15 pack.
It seems that multiple packs cause problems.

My Growatt inverters do not read the bms modules correctly. I am using Pylontech low voltage protocols. The Growatt gives me a bms warning if I unplug the CAN cable.

I feel like that with 900aH of capacity, and usually not more than a 3kw load, the drop will not be a lot.

If I had reset the SOC's early this morning, it would not have shut down.

 

[Sparkyaz]

Maybe doing a complete balance of each battery pack individually and let them balance to reset the SOC calculation?

i would also power off the BMS’s and leave them off for a bit. Then restart. Maybe a reset of the BMS will help.

 

[Sparkyaz]

I just realized the version numbers you have v15 and v19.
So thise sound like JK Bms’s.

I saw a video on youtube about those SOC’s not being accurate.

Don’t know if you happened across it. But Here it is. The Off Grid Garage does a lot of BMS testing.

 

[Ramses]

1. SoC on JK is garbage, just ignore it.
Use a Victron Smartshunt on the system.
2. Mixed-capacity batteries can create problems if you use communication, but this is not your problem.
3. The problem is with one of the cells, not the SoC.

This is how the BMS works:
- if one of the cells hits the 0 Soc Voltage (2.640 V)or OCP value (3.65V) => cut the discharge.

Why do you use the Pylontech protocol on Growatt?
JK has 006 - Growatt_BMS_RS485_Protocol_1xSxxP_ESS_Rev2.01

How I see the implementation

1. Use v19 with the biggest capacity (314Ah) as master
2. Use v15 with a lower capacity as slaves
3. Use the Growatt protocol on the master for communication with the inverter.
4. Monitor all the batteries. I use an rpi4-5 with the clasic RS-485 to USB settings wire, with this HA add-on.

If one BMS (that is not the master) shuts down, the system should still work.

 

[Doug The Builder]

Use the windows program only for updating firmware. Hitting the LiFePo4 button in windows looks like it setting everything correctly but in reality does not. I just went thru this with 17 of the JK some V15 some V19, and it was a mess for a couple days, The Li-BMS button on the Deye showed all incorrect number for charge and discharge even though they all said 200, did a reset with the android app and everything was reading correctly again.

 

[Honuz]

Hello,
I have three DIY packs, EVE LFP 304 or 314aH. I have a mix of V15 and V19 bms. V19 has .02 firmware, V15 has the last one issued (.41?).
My inverters have shut down before dawn quite a few times, with them all reading zero percent or nearly zero. I go out to the power shack
and see that the voltage is 50.4V. No where near zero percent!
I go through my exercise of going into BT and resetting the SOC by changing the pack capacity by one: from 304 to 303aH.
This sets the SOC back to some sane value. In this case of 50.4V, it came back to around 30%.

Jk bms do not include coulomb meters...do NOT use them to evaluate SOC, use a real shunt.
Bms are not here to evaluate SOC but to control the well being of cells.
You can check bms logs to see what triggered a charge/discharge cut off

 

[Ramses]

JK BMS versions 15 and 19 have coulomb meters (current shunt resistors).

 

[Honuz]

JK BMS versions 15 and 19 have coulomb meters (current shunt resistors).

Hoo did not know

But where is it ? Where did you get this information that jkbms 15 and 19 included a shunt, can't find it...

 

[Ramses]

Maybe @RCinFLA can answer that.

Post in thread 'JK-BMS v19 firmware versions'

Jul 31, 2025

It just dawned on me that the JK PB BMS has twenty 1 mΩ chip resistors in parallel for current shunt, at least in the 200 amp version. That gives a very low value shunt resistance of 0.05 mΩ and very low output sense voltage for low currents.

The low-end current capability will be severely limited by the current sense amplifier DC offset tolerance.

Looking at a v15 200 amp board, the current sense amplifier has a six pin sc70 package marking of '9A10c'. I was not able to find a spec for this part and it is likely a Chinese clone of a western part.



The closest candidates...

• RCinFLA

• 

Post in thread 'JK-BMS v19 firmware versions'

Sep 2, 2025

I've tried to calibrate voltages and amperage on my 6 x 16kWh packs.
The SoC of each battery is....

User current calibration only affects charging current. I was a bit surprised when I discovered this.

Discharge current calibration is fixed by factory setting.

V19 gets rid of DC offset dead zone with zero calibration allowed on v19.10 units. I believe the zero calibration is triggered when 0.000 is entered for current calibration value. You cannot enter zero current calibration value on v15, v14 units and they have a zero dead zone gap.

Make sure you actually have zero...

• RCinFLA

• 

 

[Honuz]

Maybe @RCinFLA can answer that.

Post in thread 'JK-BMS v19 firmware versions'

Jul 31, 2025

It just dawned on me that the JK PB BMS has twenty 1 mΩ chip resistors in parallel for current shunt, at least in the 200 amp version. That gives a very low value shunt resistance of 0.05 mΩ and very low output sense voltage for low currents.

The low-end current capability will be severely limited by the current sense amplifier DC offset tolerance.

Looking at a v15 200 amp board, the current sense amplifier has a six pin sc70 package marking of '9A10c'. I was not able to find a spec for this part and it is likely a Chinese clone of a western part.



The closest candidates...

• RCinFLA

• 

Post in thread 'JK-BMS v19 firmware versions'

Sep 2, 2025

I've tried to calibrate voltages and amperage on my 6 x 16kWh packs.
The SoC of each battery is....

User current calibration only affects charging current. I was a bit surprised when I discovered this.

Discharge current calibration is fixed by factory setting.

V19 gets rid of DC offset dead zone with zero calibration allowed on v19.10 units. I believe the zero calibration is triggered when 0.000 is entered for current calibration value. You cannot enter zero current calibration value on v15, v14 units and they have a zero dead zone gap.

Make sure you actually have zero...

• RCinFLA

• 

Well .. that's exacxtly my point, since it give innacurate information, this can't be called a shunt. You could also call a car an excavator cause you can put dirt in it .. but still .. it's not it purpose or let's say it can't be used that way.

 

[Ramses]

Blah, I'm at battery 4 (I still have 3 to test and calibrate).
I try to calibrate the Ampers. No error.
Constant Amp source 20-21A, see the variation on the BMS App.