Anyone else had their Fogstar Drift BMS trip at weird state-of-charge levels?

So I'm three months into running a 200Ah Fogstar Drift 12V LiFePO4 in the van and it's been mostly brilliant — dead quiet, compact, fits the under-bed box I built perfectly. But twice now I've had the BMS cut out when the Victron BMV-712 was still showing somewhere around 20-25% SOC. Not low-cell-voltage territory by any reasonable measure.

First time it happened I was running a 240W inverter with a small induction hob — fair enough, assumed it was an overcurrent blip. Reset it, moved on. Second time though I was barely drawing 8A through a 12V compressor fridge at the time, so that excuse doesn't hold water.

I've had a poke around and the Fogstar documentation is... let's say sparse. No way to read individual cell voltages without pulling the whole thing apart and poking a multimeter in, which I'd rather avoid. Makes me wonder if one cell is drifting low faster than the others and the BMS is doing its job, but I've got no visibility into it.

Has anyone found a reliable way to actually monitor individual cell health on a sealed unit like this, or are we all just trusting the black box? Tempted to look at a Victron Smart Lithium where you get proper Bluetooth diagnostics, but that's a significant chunk of change more.

MasterLife | Posts: 847

@OddJobBob yeah, seen this come up a few times actually. The Drift's BMS can be a bit twitchy about how fast you're discharging rather than just the absolute SoC level. If you're running something with a high inrush current — kettle, inverter-powered tools, that sort of thing — it can momentarily trip the BMS even when the cell voltage is perfectly healthy overall.

Worth checking what you were running at the exact moment it tripped. Also, are you seeing it recover on its own after a few seconds, or does it need a charge input to reset? That'll tell you whether it's an overcurrent trip or something else entirely.

What's your charging setup — any solar or just hook-up? Occasionally an imbalanced charge profile can leave the BMS a bit confused about actual capacity.

Mine tripped at 74% once — turns out my Victron MPPT was throwing a tiny voltage spike on bulk charge that the Drift's BMS interpreted as an overvoltage event, sorted it by dropping absorption voltage from 14.6V to 14.4V and it's been rock solid since. 🎯

RussMartin | Posts: 312

Worth checking your cable connections and fuse holder contacts as well — I had something similar and it turned out to be a loose ANL fuse contact creating just enough resistance to cause a momentary voltage drop under load. The BMS saw it as a fault condition and tripped even though the cell voltages were perfectly healthy.

Tightened everything up, applied some copper grease to the terminals, and haven't had a trip since. The Drift's BMS is actually quite sensitive to those kinds of transient events, which is arguably a good thing for cell protection, but it does mean your wiring needs to be absolutely solid.

@WayneTaylor's point about MPPT spikes is also worth investigating — have you checked your charge profile settings? Sometimes dropping the absorption voltage slightly sorts it.

RockySailor | Posts: 203

Good shout from @RussMartin on the connections — worth doing regardless. One thing nobody's mentioned yet: have you checked the ambient temperature in that under-bed space? LiFePO4 cells can behave oddly at the temperature extremes, and a van environment can get surprisingly cold overnight or hot in summer. The Drift's BMS has thermal protection built in, and if it's reading a borderline temperature it can trip even when the SoC looks perfectly normal on your monitor. Try logging the battery temp alongside your voltage readings for a few days — there's a thread somewhere on here where someone solved an almost identical mystery that way. Also worth confirming your battery monitor is properly calibrated with the correct Peukert exponent for LiFePO4, as wildly inaccurate SoC readings can make tripping seem random when it's actually happening at the correct voltage threshold.

Seen this with my Drift too — tripped around 80% during EV charging sessions when the draw was spiking hard. Turned out my cable sizing was marginal for the peaks, so the BMS was seeing transient undervoltage even though the average SOC looked fine.

Worth logging with a Victron SmartShunt if you've not got one already — made it dead easy to spot the brief dips that were invisible otherwise. Since I upsized the cables and added a small capacitor across the load terminals it's been solid.

@WayneTaylor's point about MPPT spikes is real too — if you're running both solar input and a load simultaneously the BMS can get confused by the combined profile. Try isolating which scenario triggers it first.

HollyGraham83 | Posts: 847

Had exactly this with mine last summer. Worth checking whether it's correlating with temperature — my Drift got a bit twitchy with BMS trips when the van interior got really warm during charging. The BMS is quite conservative on thermal protection which is no bad thing, but it caught me out a few times. I stuck a small thermometer near the battery and noticed a pattern pretty quickly. Also, are you on the latest firmware? Fogstar pushed an update a while back that apparently tweaked some of the trip thresholds. Might be worth dropping them an email directly — their support has been decent in my experience.

WD40Wizard | Posts: 847

Different context to you lot (static caravan, not a van) but I've seen similar with my Drift. Mine tripped twice during simultaneous inverter load + solar input — basically the BMS getting confused about net current direction when both were happening at once.

Fogstar's support told me this is a known edge case on early firmware. Worth emailing them with your serial number — they can tell you which firmware revision you're on. Some units shipped with an older BMS config that's a bit twitchy on sudden load spikes.

@GoldenMaker's point about charging spikes lines up with this too — it's essentially the same root cause, rapid current transitions rather than the SoC reading itself being wrong.

Standalone BMS data logger helped me nail down exactly when it was tripping. Overkill for some but made diagnosing it much faster.

LizWalker | Posts: 312

@OddJobBob interesting one — I'd be curious whether these trips are happening during charging or discharging, as that might narrow it down considerably. I had a BMS nuisance trip on a different LiFePO4 brand that turned out to be a loose busbar connection causing momentary voltage spikes that the BMS read as an overcurrent event. The actual SoC was almost irrelevant — it was just coincidence it happened at similar percentages. Worth checking all your connections are properly torqued before diving deeper into BMS settings. What's your charging source when it trips?