BSLblatt online/offline issues

Right, hoping someone here can shed some light on this before I lose what's left of my sanity.

Running three BSLbatt 48V lithium batteries in parallel on the narrowboat — been working a treat for most of the season, all talking nicely to the Victron Cerbo GX via the RS485 daisy chain through ports 4 and 5. Master unit set up correctly, slaves configured accordingly, the whole lot.

Problem is, intermittently — and seemingly at random — one of the slave units drops offline on the DVCC display. Sometimes it comes back within minutes, sometimes I'm cycling power on the whole bank to get it to play nicely again. No obvious pattern to it. Doesn't seem temperature related, doesn't correlate with high load or charge cycles. Just... decides it's had enough.

What I have noticed:

• The cable runs between units are maybe 600mm each — all proper shielded RS485 cable
• Termination resistors are fitted at each end of the chain
• Baud rate is consistent across all three units (checked this twice)

So either I've got a dodgy cable somewhere, a flaky RJ45 connection, or there's something in the BSLbatt firmware that's causing grief. Read somewhere that some batches had RS485 stability issues but I can't find anything concrete.

Has anyone else run multiple BSLbatt units in parallel and hit this? Did a firmware update sort it, or was it a hardware/wiring gremlin in the end? Getting rather tired of watching that third battery ghost in and out like it's auditioning for a paranormal documentary.

Wardy26 | Posts: 847

@AngliaCamper Sounds like you've got cut off mid-post there mate, but I reckon I can guess where you're going with this! Classic symptom with BSLbatt parallel setups is the BMS communication dropping out when one unit decides it's not quite in sync with the others — usually shows as random offline readings on your monitoring software.

Few things worth checking before anything else:

• Are all three batteries on the same firmware version? Mismatched firmware causes havoc
• Check your RS485 daisy-chain cables, particularly the termination resistor on the last unit
• What are you using to monitor them — Victron GX device?

Narrowboat environment is brutal for connections too, so give every terminal a wiggle and look for any corrosion creeping in.

Finish your original post when you get a chance and we'll get it sorted! 👍

Owen1991 | Posts: 312

@AngliaCamper Looks like your post got cut off too, ha! Great minds and all that.

Narrowboat installs can be a bit particular with parallel battery setups — worth checking your inter-battery cabling is all the same length and gauge. BSLbatt are generally solid but if one unit is seeing slightly different resistance it can cause the BMS on that pack to get a bit paranoid and drop offline, which then sometimes cascades.

Also, are you on the latest firmware? There was a batch from a while back that had some communication gremlins over the RS485 bus. Worth contacting BSLbatt directly as they're usually pretty responsive.

What's your inverter/charger setup? That might help narrow things down further.

ExFirefighter42 | Posts: 1,204

@AngliaCamper Narrowboat installs are a particular beast for BMS comms issues — that damp environment plays havoc with CAN/RS485 connections over time.

Few things worth checking beyond what @Wardy26 and @Owen1991 have likely suggested:

• Termination resistors — parallel battery setups are notorious for impedance mismatches causing intermittent dropouts
• Cable screening — narrowboat engine interference can absolutely corrupt data signals; shielded comms cable makes a surprising difference
• Victron DVCC settings if you're running a Cerbo GX — incorrect shared voltage/current sense settings will cause exactly the erratic online/offline behaviour you're describing

From my own motorhome setup running Fogstar Drift cells, I had similar ghost disconnects traced back to a single dodgy RJ45 crimp on the BMS daisy-chain. Ten-minute fix once identified.

Post your full setup details when you can — inverter/charger make, how the batteries are networked

JohnDixon | Posts: 203

@AngliaCamper Narrowboat comms gremlins... oh mate, I've been down this rabbit hole on the boat. Three BSLbatt units in parallel is exactly where the fun starts — daisy-chain the CAN bus cables wrong and you'll get random dropouts that make you question your own existence.

Few things worth checking that nobody's mentioned yet:

• Termination resistors — are both ends of your CAN chain terminated? Miss one and it goes haywire under load
• Cable routing near the inverter/charger. My Victron MultiPlus was radiating interference until I rerouted the comms cables away from the DC busbar
• BSLbatt's own firmware — worth checking if there's an update, mine had a known BMS comms bug that got patched quietly

What's your actual comms setup — USB to VenusOS, direct Victron GX, or something else? Makes a big difference diagnosing this properly.