Anyone else's MPPT controller gone completely mental in this recent cloudy weather?

My Victron SmartSolar 100/30 is throwing a wobbler — keeps dropping in and out of float at about 11:30 every morning like clockwork, even when the panels are supposedly pulling 180W through patchy cloud.

Running 200W of Renogy mono on the cabin roof feeding a pair of Fogstar 100Ah lithiums, so it's not exactly a demanding setup. Worked flawlessly all summer, now it's acting like it's had a personality transplant.

Anyone seen this with Victron gear when the light goes a bit grim? Wondering if it's a dodgy absorption threshold setting or if the British weather has finally broken my boat.

Roger1983 | 847 posts | ⚡ Solar Enthusiast

@MarineKaren that 11:30 pattern is interesting — sounds behavioural rather than a fault. My money's on your battery voltage briefly spiking above the float threshold when a cloud breaks and you get that sudden burst of irradiance, then the controller legitimately drops into float, only to absorb again seconds later as cloud cover returns. It's essentially hunting.

Worth checking your absorption voltage setpoint — if it's set quite low (say 14.1V on a 12V system) it doesn't take much of a spike to trigger the transition. You could try bumping it up slightly or adjusting the tail current setting in VictronConnect if you haven't already. The tail current threshold basically tells the controller "don't switch to float until charge current drops below X amps" which should smooth this right out.

What battery chemistry are you running?

ExpertLife | 2,341 posts | ⚡ Verified Off-Grid Installer

@MarineKaren that clockwork timing is a classic giveaway — worth checking whether 11:30 coincides with the sun clearing (or hitting) a specific obstruction like a chimney, tree line, or even a neighbouring roof. A sudden sharp spike in irradiance after patchy cloud can briefly fool the SmartSolar into thinking the battery's topped off, triggering a premature float. It's essentially the algorithm getting confused by rapid voltage fluctuations rather than a genuine full charge.

Have a look in the VictronConnect app at your absorption voltage setting and tail current threshold — if the tail current is set too high, it'll exit absorption earlier than it should. What's your battery chemistry? If you're on AGM that threshold behaves quite differently to lithium. Sharing a screenshot of your history graph would help enormously here.

WonkySkipper | 234 posts | ☀️ Cabin Dreamer

@MarineKaren my SmartSolar did something similar last autumn — turned out a cloud was basically on a commute, passing the same spot every morning 😂

Jokes aside, worth checking if anything nearby kicks in around 11:30

DanHughes | 1,156 posts | 🔋 Off-Grid Convert

@MarineKaren worth checking whether you've got parasitic loads kicking in around that time — anything on a timer? Immersion heater, fridge compressor cycling, even a router rebooting on a schedule? 180W of generation through patchy cloud can be deceptively marginal, and if something pulls a chunk of that simultaneously, the controller sees voltage sag and bails out of float sharpish.

Also double-check your absorption voltage threshold in the VictronConnect app — if it's set too high for your battery type you'll get this kind of yo-yo behaviour particularly when generation is inconsistent. What batteries are you running? AGM, lithium, leisure lead-acid? Makes a fair difference to what settings you should actually be using.

AnneWatson | 87 posts | 🌿 Shepherd's Hut Solar

Had almost identical on my hut setup last February. Worth pulling up the VRM history if you're connected — the detailed graphs showed me mine was actually hitting absorb target briefly during a cloud gap then bouncing straight to float before dropping back. Looked mental but was technically "correct" behaviour.

Also check your absorption voltage threshold. Mine was set a touch low from factory and any modest input spike was enough to trick it into thinking job done.

What battery chemistry are you running? My Fogstar lithium profiles behaved very differently to when I had AGMs — float thresholds matter a lot more with LiFePO4.

Davo79 | 412 posts | 🔧 DIY Off-Grid

@MarineKaren that clockwork timing is interesting — 11:30 sounds like it could be temperature-related rather than a fault as such. As your batteries warm up through the morning, the Victron recalculates the absorption voltage target and sometimes that triggers a brief float dip if the battery's already reasonably topped up. Worth jumping into the VictronConnect app and checking your absorption time settings — if it's set quite short, it'll punt itself into float earlier than you'd expect on a dull day. Also have a look at your battery temperature compensation settings if you've got a temp sensor fitted. Might be worth logging a few days of data through the app so you can see exactly what the voltage is doing at that point. Usually more of a settings tweak than anything sinister.