Victron MPPT 100/30 showing "absorption" all day — panels barely producing anything?

Right, bit of a head-scratcher this one. I've got a 200W panel (single Risen 200W mono) wired into a Victron SmartSolar 100/30, feeding a 100Ah lithium (Battle Born equivalent, actually a Fogstar Drift). Set everything up about three weeks ago on my Transit conversion and it worked a treat for the first fortnight — nice bulk/absorption/float cycle, battery hitting 100% by early afternoon on decent days.

This past week though, even on reasonably bright mornings, the Victron Connect app is showing "absorption" from basically the moment the sun comes up. Panel voltage is sitting around 22-23V, current maybe 0.3-0.8A, and the watts are laughable — sometimes as low as 6W when I'd expect 60-80W minimum. The battery SOC is showing around 78-80% so it's not like it's fully charged and tapering off naturally.

I've checked the obvious stuff — MC4 connections feel solid, no visible damage to the cable runs, and I re-ran the battery profile setup in VictronConnect yesterday (using the lithium preset, absorption at 14.2V, float 13.5V). Wondering if there's something I've misconfigured in the charge algorithm, or whether the panel itself might have developed a fault. Worth noting the weather's been overcast but not that bad — neighbours with grid-tied systems are still generating fine.

Has anyone seen this "stuck in absorption" behaviour on a SmartSolar before? Could a dodgy cell in the panel cause this kind of low-current symptom, or am I barking up the wrong tree?

FrankMurray replied:

@MartinParker64 Classic one this — your lithium is almost certainly already full or very close to it, so the MPPT is sitting in absorption doing nowt because there's nowhere to push the current. With a 100Ah lithium and only 200W of panel, if the battery was reasonably charged overnight (from yesterday's sun or a mains charger), a dull morning can tip it into absorption almost immediately.

Check your battery voltage — if it's sitting at 13.8V+ that's your answer. Also worth checking your absorption voltage setpoint in VictronConnect; some Fogstar units prefer a slightly lower figure than the default. What profile have you got the MPPT set to? Lithium preset or custom?

@MartinParker64 Worth checking what voltage the absorption is sitting at — if it's genuinely in absorption but producing next to nothing, that's actually correct behaviour. Lithium accepts very little current once it's near full; the MPPT throttles output accordingly rather than forcing charge in. Your 100Ah Fogstar probably filled up overnight from whatever residual was left and now it's just floating at absorption threshold.

Check your VictronConnect app — look at the "yield today" figure and the battery voltage. If voltage is sitting at 14.2V+ and current is <1A, battery's full, system's working perfectly. The label "absorption" persisting all day just means it hasn't completed absorption (dropped below the tail current threshold), not that something's wrong.

@MartinParker64 One thing worth checking — what have you got set as your absorption voltage? If it's set a touch low (say 13.8V or thereabouts), a nearly-full lithium can hold the battery at that voltage with barely any current flowing, and the MPPT just sits there in absorption thinking it's working hard when it's barely doing anything. Have a look in the VictronConnect app at the charge current figure. If it's showing less than a couple of amps, that's your answer — battery's essentially full and the panel's just topping off. Nothing to worry about really, it's working as intended. What's your float voltage set to?

@MartinParker64 had exactly this with my garden office setup — Fogstar 100Ah sitting full by mid-morning, controller just ticking along in absorption doing basically nothing. Totally normal behaviour.

Check your VictronConnect history tab — it'll show you a proper graph of what's happened across the day. If the battery hit absorption voltage early and current dropped off, that's your answer. Battery's full, not a fault.

Only thing I'd add beyond what others said — make sure your tail current is set correctly in VictronConnect. Lithium should exit absorption once current drops to around 2-4% of capacity. If that's misconfigured it'll just sit there indefinitely.

@MartinParker64 worth looking at your tail current setting in the VictronConnect app. On a 100Ah lithium, absorption ends when current drops to a set percentage of battery capacity — if that threshold is too low, the controller just sits in absorption indefinitely waiting for a condition that never triggers, even when the battery's essentially full.

Default tail current on SmartSolar units is often 1A, which for a 100Ah bank is actually reasonable, but worth confirming yours hasn't been set to something daft like 0.1A.

Also cross-reference your absorption duration — under Battery > Expert Mode you can cap absorption time directly. On lithium I typically run mine to 1–2 hours maximum rather than relying solely on tail current. Stopped exactly this phantom-absorption issue on my own 200Ah Fogstar setup last winter.

@MartinParker64 Something nobody's mentioned yet — check your battery temperature compensation settings. If you've got a temp sensor fitted (or even if you haven't and VE.Smart networking is pulling a figure from somewhere), it can artificially shift the absorption target voltage and cause the controller to sit there indefinitely chasing a moving target.

Also worth exporting your history data via VictronConnect — look at the "time in absorption" figure across the past week. On my boat setup I had a similar ghost-absorption issue; turned out the controller was seeing phantom load fluctuations keeping it from ever registering a stable tail current reading long enough to transition.

200W into a 100Ah Fogstar on a decent day should be wrapping up absorption well before noon honestly.