SOC mismatch in VRM and JKBMS

[Gaboss (Gábor Anda)]

Hi, I have the 2 phase system with following setup: 2 x MultiPlus 48/3000/35-50
1 x Venus GX
1 x MPPT 150/70-Tr
1 x Lifepo4 Battery box 48V system 16x314Ah with JK BMS.
I must admit I’m not a great technician, trying to learn the things. I bought this DIY battery box, successfully assembled. On Sunday I managed to connect the battery box to the inverter and establish a communication between Venus and JK BMS. Happy life!
Of course the battery was never charged to 100%, the JK BMS was not calibrated and showed around 60%.

On Monday everything was running OK. But today morning (Tuesday) I woke up and saw the system shoot down (error #38) I assume due to low battery voltage (I received a bunch of alerts).
I managed to revive the system. But since then the Multiplus shows SOC 100% and won’t charge the battery and still getting low battery alert.

I tried to change the battery monitoring from automatic to JK BMS, but the problem remained (for 1 second Multiplus showed the SOC according to JK BMS but then changed back to 100%).

JK BMS shows:

Something is wrong I just don’t know what. Can you pls help?

[HRTKD (Jim Egan)]

The JK inverter BMS has seen a lot of issues when in closed loop communication. The JK BMS saw a lot of hype and then a lot of disappointment. JK hasn’t done a lot to help the DIY community get past the issues.

Disconnect the communication cable and see how the system responds. I believe that the current firmware version for the BMS is 15.38.

I have the JK BMS and a Quattro 48/3000 running in open loop communication. It works fine in that configuration. Closed loop communication isn’t necessary.

[cmock (Christian Mock)]

As an alternative to no communication at all, you can also try dbus-serialbattery, which works fine with my JK inverter BMSes over RS485.

[alexpescaru]

Is it possible that you’ve enabled the inverter battery monitor and set it as the main battery monitor?

Go to Settings - System settings - Battery monitor and see what’s selected.
If on Automatic, see next line Auto selected: … what’s showing.

Also go to Settings - DVCC - Controlling BMS and see what’s there.
If on Automatic, see next line Auto selected: … what’s showing.

[lxonline (LX)]

And to add on then are the charge (absorption nad float) voltages set correctly on the inverters themselves?

Error 38 is usually when the system thinks it is overcharging the batteries and that is often related to settings.

[Gaboss (Gábor Anda)]

How do I do an open loop? I have a connection between Venus and JK BMS via CAN. Simply disconnect the cable? Thanks

[Gaboss (Gábor Anda)]

You mean LuisVDW solution? I saw it yeah, but I managed to connect the BMS via CAN port, simply choosing in BMS setup in CAN option the Victron CAN protocol.

[Gaboss (Gábor Anda)]

No, that was my first check, it was on automatic, but yesterday it worked fine. Anyway today I set it to JK BMS monitor instead of set, but that did not solve the problem, it was not charging the battery either. But when I chose „no battery monitor“, than it it passed some 1-3A to battery (it was visible on the Victron app, not the Venus).

Re DVCC I need to check. Yet the system died again. I asked a friend to charge up a smaller battery (Pylontech). I want to try tomorrow what the system will do with it.

[Gaboss (Gábor Anda)]

Can you share some example how should it be set? Thanks

[Brian]

This is how I went open loop with a JK BMS connected via CAN. Take note, this is from my notes using the old remote console interface.

• Settings > DVCC > Controlling BMS > No BMS Control
• Restarting VE.Bus System: Inverter > Advanced > Restart VE.Bus System
• MPPT > BMS Controlled > No
• Restart GX Device if necessary

Do you have a smart shunt in your system?

[Gaboss (Gábor Anda)]

Many thanks. I will try tomorrow. No I do not have smartshunt

[lxonline (LX)]

What did you set the JK bms to do? Those are the voltages to use.

If it is was just the base no edited lifepo4 one then the lithium preset will probably be ok.

[Gaboss (Gábor Anda)]

This is my BMS setup. Actually I did not change much from the default settings, only the battery capacity, continued charge curr. and CAN protocol.

[Gaboss (Gábor Anda)]

This is how the VRM looks like. You can see the SOC is jumping from 95% to 63% (this is according to JK BMS) for a second and then back.
Both Multiplus and DVCC is set to JK BMS.

[Saschaho]

Moin, first change settings in the JK-BMS : the SOC-100% Volt to 3,450V and the cell OVPR to 3,449V and your charge/discharge temps are 20°C to high.
With your high 100% settings the BMS run into cell OVP when charging.

[Gaboss (Gábor Anda)]

Ok, I will adjust the BMS setup. Thanks for help.

[Gaboss (Gábor Anda)]

Finally the system works again. The problem was this fuse:

It controlled the old battery‘s main positive connection to the Multiplus. With the battery change from pylontech to new bigger box I let the battery to get charged with higher amps and the fuse blew. This caused the alarms.

After the New battery was fully changed and balanced, both the JK BMS and MultiPlus recalibrated itself and now show the correct SOC.