Victron MPPT 100/30 showing weird absorption times since clocks changed

Saw exactly this on my cabin setup last autumn — the 100/30 was sitting in absorption for what felt like forever, then suddenly cutting short the next day. Took me an embarrassing amount of time to realise the clocks had gone back and the controller's internal clock was now an hour out.

The thing is, Victron uses time-of-day to influence the adaptive absorption algorithm, so if it thinks it's got less daylight left than it actually has, it starts making odd decisions. An hour's drift is enough to confuse it properly.

A few things worth checking:

• VictronConnect app — you can sync the clock manually when you connect via Bluetooth. Dead simple once you know it's there.
• VRM portal — if you're connected, it sometimes resyncs automatically but I wouldn't rely on it.
• Absorption voltage threshold — worth logging your battery voltage over a few days with a Fogstar or similar smart BMS if you've got lithium, just to confirm it's actually hitting proper targets before dropping to float.

Mine settled down within a day or two of resyncing the clock. Running a 200Ah lithium bank with two 175W Renogy panels on the cabin roof, so getting absorption right through October matters when you're not visiting every weekend.

Anyone else notice this every year like clockwork (no pun intended) or is it just those of us who don't visit our setups regularly enough to catch it quickly?

Turbo34 | 847 posts

@DontPanic25 Classic BST/GMT gotcha! The 100/30 calculates its adaptive absorption time based on how long the previous bulk stage took, but if the clock shift throws off the internal day/night detection it can get genuinely confused about where it is in the charge cycle.

Worth checking in VictronConnect whether you've got the "BatteryLife" algorithm enabled — that adds another layer of timing logic which can make the behaviour look even stranger around the clock change.

Quick fix that worked for me was simply doing a manual "synchronise" on the history, or in stubborn cases just resetting the charge algorithm so it starts fresh. It'll recalibrate itself after a couple of sunny days. Bit annoying but harmless overall.

PVKing | 203 posts

Does the 100/30 actually have an internal clock, or is it purely basing absorption time on voltage behaviour during the charge cycle? I always assumed it was the latter, so the clock change shouldn't matter — but clearly something's going wrong for people.

On my emergency backup setup I noticed odd absorption behaviour around the same time, but I'd assumed it was the shorter daylight hours rather than BST→GMT causing it. Now wondering if I've been blaming the wrong thing.

Is there a firmware version that addresses this? Checking VictronConnect on mine but can't immediately see anything obvious. Would be useful to know if a manual recalibration via the app sorts it or whether it resets itself after a few cycles anyway.

FormerMariner24 | 312 posts

@PVKing — no internal clock as such, but it's not purely voltage-based either. The MPPT tracks how long it took to reach absorption voltage and uses that to calculate how long to stay in absorption. If the clock change shifts when your panels start producing meaningful current (effectively losing or gaining an hour of usable morning light in the controller's "memory"), it throws that calculation off for a day or two until it recalibrates.

On my garden office setup I just manually triggered an equalisation cycle after the clocks changed last October — cleared the weirdness immediately. You can do it through VictronConnect in about 30 seconds.

Worth also checking your tail current setting if you haven't already. Too high and it'll exit absorption early regardless.

Boycie | 1,204 posts

@PVKing @FormerMariner24 worth adding — if you're running VE.Direct into a Cerbo GX or even a Raspberry Pi with Venus OS (which I do on the narrowboat), the system clock feeding the MPPT does matter and can absolutely skew the adaptive algorithm around the clock change. Mine went daft last October for about three days until I manually synced the Cerbo via the Remote Console.

Also easily overlooked: check your tail current setting in VictronConnect. If it's set too low relative to your bank size, absorption drags on regardless of clock weirdness. I've got 200Ah of Fogstar Drift LiFePO4 and bumping tail current from 1A to 4A sorted half my "endless absorption" grief before I even touched the time settings.

Two separate issues that love appearing together, basically.

Nessa68 | 847 posts

This caught me out badly in my motorhome last October. The Cerbo GX had synced its time correctly after the clocks changed, but my 100/30 was doing odd things with absorption for nearly a week before I thought to check the VE.Connect app properly.

What nobody mentioned yet — if you're not connected to a GX device and you're relying on the adaptive absorption algorithm alone, it can take several charge cycles to "relearn" after a disruption like a clock change or a few cloudy days back-to-back. Gave mine about four full sunny cycles and it settled right down.

@Boycie makes a good point about the Cerbo, but even without one, patience is sometimes the actual fix rather than any setting change.