Fogstar Drift 200Ah LiFePO4 — BMS cutting out under EV charger load, anyone else?

So here's a frustrating one. I've had a Fogstar Drift 200Ah sitting in the motorhome for about eight months now, generally brilliant, no complaints — until I started using a Type 2 portable EVSE to top up the car from the motorhome's 230V inverter. The battery BMS trips out somewhere between 18 and 22 minutes into a charging session, every single time. Victron MultiPlus 2 3000VA on the inverter side, Fogstar's own BMS doing its thing on the battery side.

I've checked the obvious stuff. The draw is around 1,800–2,000W sustained, which is well within the Multiplus spec and should be within the Drift's 100A continuous discharge rating (sitting at roughly 78–85A at 24V). Temps are fine, well within operating range. The BMS isn't throwing a temperature fault — it just goes into protection mode silently and the whole lot drops off.

My suspicion is it's a sustained-discharge timeout rather than a true overcurrent event, but I haven't been able to confirm that with Fogstar yet. Their support response times have been a bit patchy to put it politely. Has anyone pulled apart the Drift's BMS parameters or got comms working with it to see what's actually triggering the cutoff?

Wondering if this is an EV charging specifically — something about the load profile being particularly unforgiving — or whether I'd see the same behaviour running a big inverter generator or similar sustained draw.

TransitProject | 847 posts

@PanelLouise your post got cut off but I can guess where this is going! The Drift's BMS has a continuous discharge rating of 100A but the peak current draw when an EV charger initialises can spike well beyond that momentarily — enough to trigger overcurrent protection even if your steady-state draw looks fine on paper.

Few things worth checking: what's your cable run length and cross-section to the charger? Volt drop can cause the EVSE to demand more current than expected. Also, is this happening at initial handshake or mid-charge?

The Drift BMS should auto-recover after a short delay — are you getting full cutout requiring manual reset, or just a momentary trip?

Worth measuring actual peak draw with a clamp meter if you have one. Might also be worth contacting Fogstar directly — their support is generally decent in my experience.

MasterAdventure | 312 posts

Yeah I've been down this exact rabbit hole — I run a Drift on my boat for EV charging top-ups when I'm at marina without hookup.

The issue is the BMS peak current threshold vs sustained draw. EV chargers pull hard and steady, which is a different beast to an inverter spike. The Drift's BMS doesn't always love that sustained demand.

Few things worth trying:

• Check your cell balancing — if one cell's lagging, BMS trips early
• Dial the EVSE down to 6A or 8A temporarily and see if it holds
• Make sure your cabling is properly rated — voltage drop can confuse things

Fogstar support are actually decent, worth dropping them a message directly. They've pushed firmware updates for BMS behaviour before on some units.

What's your total battery bank — just the single 200Ah?

Thommo40 | 203 posts

@PanelLouise the post cutting off is killing me, but I reckon I know the issue! Had something similar with my Drift 200 — the culprit for me was inrush current when the EVSE handshakes and starts the charging session. The BMS sees that initial spike and trips on overcurrent protection before the actual sustained draw even begins.

What worked for me was adding a softstart device (I used a Victron Energy via a small inverter setup) to cushion that initial surge. Also worth checking your cable connections are properly torqued — a slightly loose terminal creates resistance which compounds the problem massively.

What EVSE brand are you using? Some of the cheaper portables have quite aggressive startup profiles. Also, what's your current SOC when it trips? Mine was more prone to tripping below about 30%.

ShaunJohnson | 521 posts

@PanelLouise yes, classic inrush current trip — the EVSE negotiates its charge rate and then throws a sudden load spike at the BMS that it interprets as a fault condition. Worth checking whether your Drift's BMS has a configurable overcurrent threshold; some firmware versions are quite aggressive at protection.

Practical suggestion before anything else: try setting your portable EVSE to its lowest amperage setting (usually 6A on most Type 2 units) and see if the cutout still happens. If it behaves at 6A but not higher, you're likely hitting the peak detection threshold rather than sustained overcurrent. A small pre-charge resistor arrangement can also soften that initial spike considerably.

What inverter/charger are you running alongside it, if any? Sometimes it's actually compounding loads rather than the EV charger alone causing the trip.

OffGridMick | 847 posts

@PanelLouise one thing nobody's mentioned yet — check what your BMS overcurrent threshold is actually set to versus the continuous draw. The Drift's BMS is rated for 100A continuous discharge, but if your EVSE is pulling anywhere near that and you've got any other loads running simultaneously (fridge, inverter, lighting), you could be nudging the BMS into protection even without a dramatic inrush spike.

Worth grabbing a clamp meter and monitoring actual draw during the charge negotiation phase. Also, what inverter/charger are you running between the battery and the EVSE? If there's a separate inverter involved, its own startup behaviour could be compounding things.

Some folks have had luck reducing the EVSE's max current via the pilot signal settings if your unit allows it.

Stacey26 | 178 posts

@PanelLouise I had almost identical bother with mine, though it was a smaller inverter rather than an EVSE causing the trip. What sorted it for me was fitting a pre-charge resistor circuit to smooth out that initial current spike before the main contactor closes. Fairly straightforward DIY job if you're comfortable with electrics. Also worth double-checking your cable run between the battery and the inverter/charger — any excess resistance there can actually make inrush worse rather than better.

@OffGridMick makes a good point about the BMS threshold too. Some of the Fogstar units ship with fairly conservative overcurrent settings that you can adjust via the app if yours has Bluetooth comms. Might be worth looking at that before spending money on hardware solutions. What's your current cable gauge out of interest?