High Voltage Alarms

Been through something almost identical with my shepherd's hut setup last spring, so this thread caught my eye immediately.

I'm running a single Victron SmartSolar 100/50 into a 200Ah Fogstar Drift LiFePO4, and for the first few months everything was rock solid. Then come April — longer days, panels finally getting proper sun after a grim winter — the Victron app started throwing high voltage warnings and my cheap inverter was tripping out at odd hours.

Took me an embarrassingly long time to work out what was happening. The battery was reaching full absorption faster than I'd accounted for, and because I'd never bothered properly setting the float voltage, the controller was essentially holding the battery at a voltage the inverter didn't like.

The fix for me was twofold:

• Dialling back the absorption voltage slightly (went from 14.6V to 14.4V)
• Making sure float was set correctly at 13.5V rather than whatever factory default I'd left it on

If you're running two MPPTs into the same bank, I'd also be checking that both controllers are networked together and not fighting each other — on Victron kit that means VE.Smart Networking so they're sharing battery sense data and synchronising charge phases.

Worth asking: has your battery bank recently got fuller quicker because the weather's improved? Spring and early summer can catch people out after months of marginal solar.

Curious whether others have noticed seasonal triggers for this kind of thing — feels like it doesn't get talked about enough.

@MuddyNomad snap — shepherds hut with a Fogstar Drift and Victron SmartSolar is basically my entire personality at this point, so I feel your pain on the high voltage alarms. Nine times out of ten it's your absorption voltage set slightly too optimistic in the VictronConnect app — Fogstar's own recommended charge profile is worth a second look because it's a touch more conservative than whatever Victron defaults to out the box.

@MuddyNomad what's the actual alarm you're getting — high voltage on the battery side or the PV input? Makes a difference to where you start looking.

Common culprit with that combo is absorption voltage set slightly too high in the SmartSolar profile. Fogstar Drift wants 14.6V absorption, 13.6V float. If someone's used a generic lithium preset it can drift a bit outside that.

Also worth checking your BMS cutoff threshold — the Drift's built-in BMS will disconnect at overvoltage and the Victron then sees a load dump which can spike the readings.

What does VictronConnect show in the history tab? The peak voltage logged there will tell you whether it's a genuine overvoltage event or just a sensor/comms glitch.

@GlenDoug is asking exactly the right question — that distinction is crucial.

@MuddyNomad if it's PV input high voltage, your panel string VOC is likely exceeding the 100V limit, especially on cold mornings when VOC climbs. Check your panel specs and calculate worst-case VOC at -10°C using the temperature coefficient.

If it's battery-side high voltage, the SmartSolar's absorption/float setpoints are misconfigured for the Fogstar Drift's lithium profile. The Drift L wants:

• Absorption: 14.2V
• Float: 13.5V
• Charge algorithm: Li-ion preset or custom

Common culprit is someone accidentally leaving it on the AGM profile — the 14.7V absorption will absolutely hammer a LiFePO4 and trigger the BMS overvoltage alarm.

Connect via the VictronConnect app and double-check your charge profile. The Drift's documentation has the exact recommended settings if you've lost the sheet.

@GlenDoug and @DailySolar are right to pin that down first, but I'd add a third possibility worth checking: if you're on a shared battery bank with any other charge sources (shore power charger, generator input, etc.), you can get a brief high-voltage condition on the battery side that the SmartSolar reports even though it wasn't responsible for causing it.

Had exactly this on my static caravan setup — Victron was screaming high voltage alarms but the culprit was actually a cheap mains charger I'd left connected, pushing the Fogstar Drift beyond its absorption ceiling. The SmartSolar was just the one reporting it.

@MuddyNomad — worth checking your VictronConnect history logs. They timestamp each alarm event and you can often correlate it with when other loads or sources came on.

Good shout from @GlenDoug and @DailySolar on pinning down which side the alarm is on — that's step one for sure.

One thing nobody's mentioned yet: check your absorption voltage setting in VictronConnect actually matches what Fogstar specifies for the Drift L. I had mine defaulted to 14.6V when Fogstar actually recommends 14.4V for that cell chemistry. Doesn't sound like much but it was enough to trigger alarms on warm days when the battery was already a bit toasty.

Worth also checking whether you've accidentally enabled equalisaton — it's off by default but easy to switch on without realising. That'll push voltage well above normal charge levels.

The SmartSolar app logs are your friend here — pull up the history tab and you'll see exactly when and at what voltage the alarm fired. Makes diagnosing this much faster.