Keine Verbindung zwischen MP II 3000 GX und JK BMS

Anyone else had the joy of trying to get a JK BMS talking nicely to a Multiplus II GX without wanting to hurl the whole lot into a skip?

Setting up my static caravan with a 16s LiFePO4 pack and I've gone down the rabbit hole of getting proper BMS comms working — thought I'd cracked it on my own setup but now trying to replicate it for a family member and suddenly it's decided to be completely useless.

My original rig runs VenusOS on a Raspberry Pi sitting between the JK and the MP II, and once I got the RS485 cable wired correctly (it's always the cable, isn't it) it pulled through beautifully — cell voltages, temps, SoC, the lot showing up in the Victron portal like a dream.

Second build though? Nothing. Same components, same cable pinout, same VenusOS version. The JK BMS driver just sits there looking smug and reporting no device found.

Few things I'm currently suspecting:

• Baud rate mismatch — JK units aren't always consistent from firmware to firmware
• USB-to-RS485 adapter quality — the cheap ones from you-know-where are a lottery
• Driver version on VenusOS possibly needs updating manually

Has anyone successfully got a JK BMS integrated via the GX device directly (no Pi middleman) using the built-in Venus on the MP II GX? Curious whether skipping the Pi entirely simplifies things or just creates different headaches.

Keen to hear from anyone who's wrestled this particular beast into submission. 🐉

@MasterWanderer oh the JK BMS / Victron handshake saga — a classic!

Quick question though: are you connecting via the RS485 to USB cable or going the CAN bus route? Makes a significant difference to which protocol you're fighting with.

On my boat I wasted about three weekends convinced the BMS was

@MasterWanderer been through this exact nightmare with my narrowboat setup last year.

The thread title's in German which is throwing me but assuming you're on the RS485 to VE.Can route — double check your baud rate settings in the JK app. Mine was defaulting to something daft and the GX just sat there seeing nothing.

Also worth checking:

• JK firmware is up to date
• VE.Can termination resistor is actually enabled on the GX side (buried in the settings menu)
• You've got the right cable pinout — there's a few floating around online that are just wrong

Once I cracked it the DVCC integration was rock solid. Victron's just fussy about the handshake being exactly right before it'll play ball.

What firmware version is your MP II GX on?

@MasterWanderer the skip is a perfectly rational response, I won't judge you.

Had this exact circus with my boat build. The magic ingredient nobody tells you upfront: VE.Direct to USB adapter plus the correct DVCC settings in the GX menu. Without DVCC configured properly the Multiplus basically just ignores the BMS

@MasterWanderer been down this rabbit hole myself during my van build — cost me a good weekend and several cups of tea I didn't enjoy.

The JK BMS needs to be in Bluetooth + RS485 mode, not the default setting. Key steps that fixed mine:

1. In the JK app, set protocol to PACE BMS (counterintuitive, I know)
2. Use a proper RS485 to VE.Direct cable — cheap eBay ones caused me endless grief; I eventually used a quality unit from DALY accessories suppliers
3. On the GX side, set the DVCC settings to SVS and SCS enabled

Once Venus OS recognises the BMS correctly, you'll see it listed under CAN-bus BMS in the device list.

Also worth checking your Venus OS version — anything below 3.10 had known JK compatibility issues.

@MasterWanderer one thing nobody's mentioned yet — double-check your RS485 cable pinout isn't swapped. JK BMS uses A/B inverted relative to what Victron expects on some firmware revisions, so you can have what looks like a perfect physical connection and the GX just sits there reporting no device found.

In VictronConnect, set the BMS to "BMS 2" not generic RS485 — took me embarrassingly long to figure that out on my motorhome build.

Also worth checking: JK's UART/RS485 port shares functionality depending on which cable came in the box. Some suppliers (even reputable UK ones) ship the wrong adapter. Confirm yours is genuinely RS485 and not a UART-to-USB cable wearing a disguise.

Cerbo GX firmware v3.x+ improved JK compatibility significantly — if you're on anything older, update that first before chasing hardware gremlins.