Anyone else running Fogstar Drift lithium in a camper? Seeing weird BMS dropouts

Been running a 200Ah Fogstar Drift LiFePO4 under the bed in my Transit for about 8 months now. Generally happy with it but getting occasional BMS cutouts at around 20% SOC — Victron Cerbo is showing low voltage disconnect even though the battery's nowhere near actually flat.

Wondered if it's a comms issue between the Cerbo and the BMS, or if the Fogstar's protection thresholds are just set a bit aggressive from the factory. Tried tweaking the low voltage alarm settings in VictronConnect but still seeing it maybe once a fortnight.

Running a 300W Renogy panel on the roof into a SmartSolar 100/30, and a Victron MultiPlus 12/1200 for the inverter side. Setup's been solid otherwise — just this one niggle that's bugging me.

Anyone had similar with the Drift range, or managed to get proper DVCC comms working with it? Not sure if the BMS even supports that properly.

@JimKelly not in a camper but running a similar Fogstar Drift setup on my boat, so might still be relevant.

Had exactly this — BMS dropout that looked like low SOC but wasn't really. Turned out my Victron BMV-712 SOC calibration was drifting and the actual battery voltage was fine. The Cerbo was triggering a low-voltage disconnect based on bad SOC data rather than real cell stress.

Worth checking:

• Synchronise your BMV by letting it charge to 100% properly so it resets
• Look at individual cell voltages if you can — does the Cerbo show any cell imbalance at that 20% point?
• Check your low-voltage cutoff settings in VictronConnect — might be set slightly high

Could also just be a genuine weak cell if it's been through any heavy discharge cycles. What are your charge parameters set to?

@JimKelly funny timing — I've got a Drift 200Ah on my boat and went through almost the same head-scratcher last winter.

What eventually nailed it for me was the low-temp cutoff triggering prematurely. The BMS is quite conservative and the sensor placement inside means it can read colder than the actual cells. Under a Transit bed, especially in winter, you might be hitting that threshold right around the 20% mark when voltage sags pull the numbers down simultaneously.

Try logging your battery temperature via the Cerbo when it next drops out. Mine was cutting at what the BMS thought was borderline low-temp, combined with a voltage dip under load.

Also worth checking your negative busbar connections — a slightly loose bolt creates enough resistance to spook the BMS into thinking there's a problem that isn't really there. Found that one the hard way during a crossing to Calais.

@JimKelly I've got a Drift 200Ah in my Sprinter and went through something similar around month six. Worth checking your low voltage disconnect setting on the Cerbo — I found mine was cutting out prematurely because the BMS and the Victron weren't quite agreeing on what "20%" looked like under load. The voltage sag under a heavy draw (compressor fridge kicking in, for instance) was triggering the BMS before the Cerbo could react.

What I did was drop my Cerbo's LVD threshold slightly and add a small delay before disconnect. Sorted it completely. Also worth checking your battery temperature — these Drifts don't love the cold and the BMS gets more protective below about 5°C. Being under the bed helps but Transit floors can get properly chilly in winter.

What inverter/loads are you running when the dropout happens?

Hey @JimKelly, had a similar thing with my Drift 200Ah last summer. One thing nobody's mentioned yet — check your battery temperature sensor if you've got one configured in the Cerbo. Mine was triggering low-temp protection cutouts because it was reading slightly off, even though the actual battery was fine. The BMS and the Cerbo were essentially arguing over the SOC threshold.

Also worth looking at your discharge current settings in VictronConnect — if you've got any sharp loads kicking in (compressor fridge cycling, inverter startup surge), that can sometimes spook the BMS at lower SOC levels where internal resistance is naturally a bit higher.

What does your Cerbo show just before the dropout — any alarms logged? That'd help narrow it down considerably.

HarryWalker · 47 posts

@JimKelly worth looking at your low temperature cutoff settings if you haven't already. The Drift BMS is fairly conservative with cold protection, and under a Transit bed in winter the battery can get surprisingly chilly overnight — I've seen the BMS trip at temps that feel perfectly mild to you sat in the cab.

Also, are your Victron charge parameters set specifically for LiFePO4? A slightly mismatched absorption voltage can cause the BMS and the Cerbo to disagree about actual SOC, making 20% look like a hard floor when it isn't really.

What's your load profile when it trips — high draw appliance or just steady background consumption? That'd help narrow it down between a genuine protection event versus a communication glitch between the BMS and Cerbo.

Not a camper setup but running a Fogstar Drift 100Ah in my garden office and had a BMS dropout that stumped me for weeks. Turned out my Victron SmartShun SOC calibration had drifted badly — the Cerbo was reporting 20% but the battery was actually closer to 10-12% real SOC. A full charge-discharge cycle to recalibrate the shunt sorted it completely.

Worth checking: are your charge/discharge parameters in VictronConnect actually matched to Fogstar's recommended settings for the Drift specifically? I found the default Victron LiFePO4 profile was slightly off compared to what Fogstar specify in their docs.

@HarryWalker makes a good point about low temp cutoff too — does your Transit sleep outside overnight? Even mild UK winters can trigger that more than you'd expect.