I’m currently running an off-grid system consisting of:
3x Victron MultiPlus 5000VA (single-phase)
1x RS450/200 SmartSolar MPPT
1x MPPT 150/45 + 1x MPPT 250/100
75kWh LiFePO4 storage (5x DIY 48V battery banks)
Each battery uses a JK-BMS with Bluetooth/RS485
Full system monitoring integrated in Home Assistant and Victron VRM via Venus OS
Each JK-BMS reports charging/discharging currents accurately when the system is idle or lightly loaded (±20–30A). However, I encounter a strange issue under high PV load:
When I start charging my EV (7.2kW), and the MPPTs are covering the entire load (float voltage is correctly maintained), each JK-BMS shows a discharge current of around –20A, even though the Victron SmartShunt reports near-zero battery current (±1A), which is confirmed via clamp meter measurements both on each battery and on the common busbar.
In summary:
VRM & clamp meters show correct current: ~0A (float maintained, PVs power the EV directly)
Each JK-BMS falsely reports ~–20A discharge
PV production and voltage regulation are normal
The discrepancy appears only when all loads are PV-powered and system is in float
All BMSs are paralleled with common positive and negative busbars
JK-BMS shunts are on the negative line (default)
I’m wondering:
What could be causing this false discharge reading on each JK-BMS?
Could this be due to ground loops, shared GND between MPPTs, MultiPlus and BMSs, or some interference?
Has anyone else experienced this behavior with JK-BMS in multi-pack setups?
Any suggestions or insights would be greatly appreciated!
Yes, that’s exactly how it is in my system. The JK inverter BMS displays charging currents reasonably accurately, but discharge currents are extremely high. This was introduced with one of the recent firmware updates to determine the SOC somewhat accurately.
For example, with a discharge current of -18A, I only measured -12A with the clamp ammeter.
Interesting, guys. What type/version of JK-BMS are you using? And what firmware?
Please note that I have currently two racks with 8 x 16 x 314Ah cells so the draw here is always peanuts. And AC coupled PV only. Maybe that is why I can’t confirm this issue.
Note: not all packs are mine. I make/sell these, and need to test all of them.
I also noticed that when I charge the car in the evening with 7.2 kWh, with 500W coming from the MPPTs and the rest from the batteries, Home Assistant shows a total battery consumption reported by the BMSs of 7.8 kWh. However, in reality, it’s only 7.2 kWh + 500W from the MPPTs. But most important, when mppt’s are going off, the jk bms’s are reporting correct discharge current. May be is a link between jk’s, mppt’s and (high) load. Because on regular 3-4Kwh loads, the reported currents by jks are correct.
Not in my case. The fact that the discharge currents reported by the JK Inverter BMS are significantly too high isn’t related to the MPPTs in my case; it’s reproducible. However, it only occurred with the firmware update, which was supposed to solve the well-known SOC problem. Previously, the SOC was always reported too high (in my case with a 16s system at only 49V, 50% SOC was reported).
The update solved the SOC problem, but it reported excessively high discharge currents. I can only assume that JK used a cheap trick to reduce the excessive SOC, namely by simply calculating excessively high discharge currents. However, they could have done this more cleanly by reporting correct discharge currents and only giving the discharge currents a greater weight in the SOC calculation.
My BMS: JK Inverter BMS JK_PB2A16S20P, hardware version V15A, firmware version V15.35
So do I. But the problem isn’t so big that I’d buy a SmartShunt just because of it. I’m fine with the incorrect discharge current specifications. A halfway decent SOC is much more important to me, and that seems to be OK with the JK inverter BMS and it’s new firmware.