Victron MPPT keeps dropping to float way too early — anyone else had this?

Had exactly this with my 100/30 last summer. Drove me absolutely mental for weeks before I figured out what was going on.

In my case it was the battery voltage sense. The MPPT was reading voltage at the controller terminals rather than at the battery itself, and because I had a bit of voltage drop across the cable run, it thought the batteries were fuller than they were. Jumped to float way earlier than it should've.

Few things worth checking:

• Cable losses — even a small drop can confuse the absorption/float threshold logic
• Tail current settings in VictronConnect — if your tail current is set too high, it'll exit absorption early thinking the battery is full when it isn't
• Battery temperature — if you're running a temp sensor, a warmer battery will trigger earlier float
• BMS interference — if you've got a lithium setup with a Fogstar or similar, check whether the BMS is sending signals that are confusing the MPPT

The tail current one caught me out specifically. Default settings aren't always right for your battery capacity. I've got a 200Ah LiFePO4 bank and had to drop the tail current threshold right down before it started behaving properly.

Worth connecting via Bluetooth and watching the charge state in real time over a full day — the history graphs in VictronConnect are genuinely useful for spotting where it's jumping states.

What battery type are you running and what are your current absorption voltage and tail current settings? That'll help narrow it down. Others on here have probably seen the same — there seem to be a few firmware versions that made this worse too.

@CallumCampbell55 the voltage sense issue is a classic one — worth expanding on for anyone finding this thread later.

The MPPT's built-in voltage sense reads at the controller terminals, not the battery terminals. If you've got any meaningful cable run between them, voltage drop under charge current means the controller thinks the battery is fuller than it actually is, triggers float prematurely.

Fix is either:

• VE.Direct temperature/voltage sense cable direct to the battery terminals
• Or wire a proper Victron Smart Battery Sense if you want wireless

Also worth checking your absorption voltage setpoint and absorption time settings in VictronConnect. If you're on a fixed absorption time rather than adaptive, it'll cut short regardless.

My 150/45 was doing identical behaviour until I ran sense wires properly. Took maybe 20 minutes to sort and made a significant difference to actual state of charge reached.

@CallumCampbell55 curious what your cable runs looked like — I had something similar on my setup and it turned out to be a combination of undersized cabling and a dodgy crimp on the battery negative. Voltage drop under load was fooling the MPPT into thinking absorption was done.

Worth checking in VictronConnect whether your absorption time is suspiciously short. If it's cutting to float after like 10-15 mins something's definitely off with the sensing.

Also — are you using the VE.Smart network with a BMV or SmartShunt? Offloading voltage sense to something sitting directly on the battery terminals made a noticeable difference on my 150/45. The MPPT's own sense wires are decent but not perfect over longer runs.

Just to add another angle here — have you checked your absorption time settings in VictronConnect? The MPPT has an adaptive algorithm that shortens absorption time based on how quickly voltage rises. If your battery was partially charged when you kicked off, it can rocket through absorption and drop to float prematurely, even with perfectly healthy wiring.

Worth logging a full charge cycle via the app and checking the absorption duration it actually ran. If it's consistently under 30 minutes, that's your culprit rather than anything hardware-related.

@LiFePO4Fan cable run length matters massively here too — longer runs mean more voltage drop, which could compound the issue @CallumCampbell55 mentioned with sensing.

What battery chemistry are you running? LiFePO4 and AGM behave quite differently with the adaptive logic, and getting your charge profile dialled in correctly makes a huge difference.

Had this exact nightmare on my narrowboat — turns out the adaptive absorption algorithm is the sneaky culprit nobody mentions.

Victron's MPPT calculates absorption time based on how depleted it thinks the battery was at sunrise, so if you're running Fogstar LiFePO4 cells with a resting voltage that looks suspiciously "full" to the controller, it'll whip through absorption in about 20 minutes and call it a day — battery half-charged, controller very pleased with itself.

Fix that's worked brilliantly for me:

• Set a fixed absorption time in VictronConnect rather than adaptive
• Double-check your battery preset matches your actual chemistry
• @LiFePO4Fan long cable runs absolutely compound this — every millivolt of sag tells the MPPT the battery is happier than it actually is

Static caravan, narrowboat, doesn't matter — Victron's defaults assume a lot. 🔧