Victron MPPT keeps dropping out mid afternoon - anyone else had this?

Had this exact issue on my boat last summer. Turned out to be thermal shutdown on the Victron 100/30 — it was mounted in a spot that got direct sun through a hatch in the afternoon. Moved it somewhere with better airflow and it sorted itself out completely.

Worth checking a few things:

• VictronConnect app — hook up via Bluetooth and check the history tab. It'll show if it's been throwing thermal or overvoltage warnings
• Panel voltage — if your panels are getting very hot mid-afternoon, Voc can actually drop enough to cause weird behaviour depending on your setup
• Input voltage — are you near the top of the controller's rating? Hot days can push things oddly

Also had a mate with a similar symptom that turned out to be a dodgy MC4 connector on the panel side. Intermittent connection, showed up worst when the cable expanded in the heat.

What controller model is it and what's your panel config? Makes it easier to narrow down. Also worth posting your VictronConnect screenshots if you can grab them during the dropout — the data logs are genuinely useful for diagnosing this stuff.

Not uncommon on boats either where ventilation is rubbish and everything runs hotter than it should. Is your install in an enclosed space?

@BazBurns had the exact same thing on my cabin setup — but in my case it wasn't direct sun, it was simply mounting it flush against a poorly ventilated wall panel. The Victron 100/50 was throttling right back between 1-3pm on hot days.

Worth checking your VictronConnect app history — the thermal derating graph is really telling. Mine showed it was shedding about 40% output before I'd even noticed anything was wrong.

Fixed it by adding a 50mm standoff from the wall and a small 12v fan on a temperature switch. Hasn't dropped out since, even during last July's heat.

The Victron units are brilliant but they really do need airflow — the manual's minimum clearance recommendations aren't just suggestions.

Good thread. On my narrowboat I had a similar pattern — dropout happening consistently around 2-3pm on hot days.

Worth checking the actual temperature in the VictronConnect app if you haven't already. The 100/30 logs it and you can see exactly when thermal protection kicks in. Mine was hitting 60°C+ inside a poorly ventilated locker.

A few things I'd add beyond what @BazBurns and @WingAndPrayer have covered:

• Cable sizing — undersized cables create heat at the terminals, compounds the problem
• Charge current setting — if you're pushing it near its 30A limit constantly, try derating it slightly during summer
• Victron's own guidance says derate by ~1.25% per °C above 40°C ambient

Is yours a 100/30 or different model? The larger units seem more prone to this in my experience.

@BazBurns @ExFirefighter interesting timing on this thread — I've just been commissioning a garden office setup and had something similar crop up during the recent warm spell.

Mine turned out to be the absorption phase hitting target voltage early (battery was already fairly full from the morning), so the MPPT looked like it was dropping out but was actually just doing its job. Checked the VictronConnect history and the pattern was obvious once I knew what to look for.

Worth ruling that out before assuming thermal issues — especially if you're running a well-sized battery bank relative to your panels. The VictronConnect app graphs are genuinely useful here; 48 hours of data usually tells the story pretty clearly.

What's the state of charge on your batteries typically looking like at that point in the day?

Good diagnostic thread. One thing nobody's mentioned yet: check your battery voltage isn't hitting absorption ceiling earlier than expected on those hot afternoons. The MPPT will throttle right back and can look like a dropout if your temp-compensated charge voltage is miscalculated.

On my narrowboat I run a Victron SmartSolar 100/50 with the Smart Battery Sense dongle — it feeds real battery temp to the controller and adjusts charge voltage accordingly. Without that, the MPPT is essentially guessing, and on a hot hull in July it can get that wrong badly enough to trigger false "full battery" behaviour.

Also worth pulling the VictronConnect history tab. It'll show whether you're seeing a genuine thermal shutdown code or an absorption/float transition. Two completely different problems with different fixes. Don't just assume thermal without checking the data first.