Victron MPPT keeps dropping out on cloudy days — anyone else had this?

Had this exact issue on my boat last winter — drove me absolutely mental for weeks 😅

Mine turned out to be the absorption voltage threshold being set too high. On dull days the panels just couldn't consistently hit it, so the controller kept cycling in and out trying to find its feet. Dropped the absorption voltage by about 0.3V and it sorted itself right out.

Few things worth checking:

• Panel voltage — are your VOC figures actually suited to the MPPT model you've got? Some of the smaller Victron units can be fussier than you'd expect
• Wiring connections — had a dodgy MC4 connector that only showed up as a problem on low-irradiance days when current was minimal
• Battery state — if they're already near full, the MPPT will naturally back off, which can look like a dropout but isn't really

Also worth popping into VictronConnect and checking the history tab — gives you a proper picture of what's happening across the day rather than just guessing from the LED behaviour.

What MPPT model have you got and what panels are you running? Makes a difference — my 100/30 behaved differently to the 75/15 I had before it.

Fogstar batteries can also sometimes report odd state-of-charge figures that confuse the controller, just flagging that in case you're running their lithium cells.

Curious whether anyone else has seen this more with certain panel brands — wondering if it's a broader pattern 🤔

@ExChippie94 classic Victron behaviour — works perfectly on the one sunny day a year we get in the UK, then throws a wobbler the moment a cloud drifts over the Pennines 😄

Had similar grief with my garden office setup. Turned out my absorption voltage was set for a Mediterranean lifestyle my batteries were absolutely not living. Dropped it

@ExChippie94 worth checking your panel voltage under load on those grey days too — I had something similar on my narrowboat and the culprit was actually the cable run being slightly undersized. Voltage drop meant the MPPT was seeing the array dip below its minimum operating threshold intermittently, so it kept cycling.

Ran the numbers properly using the Victron MPPT calculator and realised my 6mm² cable over a 7-metre run was marginal once you factor in cold resistance values.

Upsized to 10mm² and the dropout behaviour almost completely disappeared. The controller itself was fine throughout — just starving for voltage headroom.

Might be worth logging with VictronConnect over a full overcast day and looking at the input voltage trace rather than just the output. The pattern of dropouts usually tells you whether it's a threshold issue or a supply issue.

@ExChippie94 this took me ages to figure out on my own boat setup. What finally cracked it for me was dropping into the VictronConnect app during an overcast morning and watching the MPPT cycle in real time — you can actually see it hunting for the MPP when irradiance is patchy.

Worth also checking your battery temperature compensation settings if you're using a BMV or Smart Shunt with a temp sensor. In winter the compensation can push absorption voltage higher right at the moment your panels can least deliver it — classic vicious cycle.

I run a Victron SmartSolar 100/30 and once I dialled back absorption by about 0.3V and enabled the ESS assistant properly, the drop-outs basically stopped. Sometimes the defaults just aren't right for UK winters.

@ExChippie94 had almost identical grief with my shepherd's hut setup last autumn. Worth checking your battery temperature compensation settings — Victron's default assumes 25°C and in a UK winter your battery bank is sitting at maybe 8–10°C, which shifts the target voltages noticeably. If the MPPT is chasing a voltage the panels simply can't reach on a grey November afternoon, it'll keep resetting.

In VictronConnect you can either enable proper temp compensation (assuming you've got a temp sensor wired in) or manually nudge the absorption voltage down a touch for the colder months. Made a real difference on my Fogstar lithium bank once I sorted it.