Anyone else had grief with JBD BMS cutting out under high load on a narrowboat?

Been running a 200Ah LiFePO4 bank on my narrowboat for about eight months now — two 100Ah cells in parallel, JBD 100A BMS from Fogstar, paired with a Victron SmartSolar 100/30 and a 2000W pure sine inverter. Setup has been solid for most of it, but lately the BMS is tripping the low-voltage cutoff when I run the inverter hard (kettle + laptop + nav screen simultaneously), even when the cells are sitting at a healthy 52V resting.

Pulled the data from the Xiaoxiang app and the voltage sag under that load is dragging individual cell groups down to around 2.9V momentarily — enough to trigger the protection. The BMS is rated 100A continuous but I'm genuinely not sure it's delivering that cleanly. Ambient temps in the engine bay aren't helping; it got up to 38°C last week with the engine running. I've read that thermal throttling can quietly derate these JBD units but I can't find solid numbers anywhere.

Considering swapping to a Daly Smart BMS or stepping up to a Victron Lynx/BMS 200 setup, but the cost difference is significant. Has anyone run a JBD long-term on a boat with similar intermittent high loads? Curious whether the fix is the BMS itself, better cell balancing, or whether I just need to be more disciplined about load management.

Hey @SunnyDrifter, classic JBD issue this one. Worth checking your BMS app (Xiaoxiang if you're not already using it) to see exactly which protection is triggering — it'll tell you if it's overcurrent, low voltage sag, or temperature.

My money's on instantaneous overcurrent rather than sustained load. The JBD 100A units can be a bit twitchy with the peak current setting — there's a separate "overcurrent protection delay" parameter in the app that defaults quite aggressively. Try bumping that delay up slightly before you go changing anything else.

Also worth checking your cell connections and busbars are properly torqued — resistance at the terminals causes voltage sag which the BMS reads as a low cell event under load. Happened to me before I realised my terminals had worked loose over a few weeks of canal vibration.

What inverter loads are you actually hitting when it cuts?

@SunnyDrifter had almost identical grief with a JBD setup on my static caravan before I moved to a Victron SmartShunt + dedicated BMS combo.

Few things worth checking that nobody's mentioned —

Cell-level voltage sag is usually the culprit rather than aggregate pack voltage. Under 2kW load your weakest cell could be hitting the undervoltage cutoff while the pack average looks fine. Xiaoxiang will show you individual cell voltages in real time — run the inverter at full load and watch them.

Also check your busbar and cable termination torque. I had intermittent cutouts traced to a single loose M6 terminal introducing enough resistance to spike the BMS protection circuit.

What gauge are your battery-to-inverter cables and what's the run length? 2000W through undersized cable causes enough voltage drop to confuse the BMS into thinking cells are sagging when they're not.