Victron MPPT keeps dropping to float way too early — 48v system

Had the exact same issue with my 48v cabin setup last year. Turned out my battery voltage sense was off — the MPPT was reading slightly higher than actual due to a dodgy connection on the sense wires. It hit the absorption threshold early, sat there a few minutes, then dropped to float thinking the job was done.

Few things worth checking:

• Battery settings — are you using the default Victron profile or a custom one? The default absorption voltage for 48v lithium and AGM are very different
• Absorption time — in VictronConnect, check your "tail current" setting if you're on a smart battery. If it's set too low it'll exit absorption early
• Wiring voltage drop — long cable runs can cause the controller to see inflated voltage at the terminals

What battery chemistry are you running? Makes a big difference to how you'd troubleshoot this. Fogstar lithium cells behave quite differently to a lead-acid bank under charge.

Also worth checking if you've got a BMV-712 or SmartShunt on the system — if so, enable network voltage sensing in VictronConnect so the MPPT uses battery-side voltage rather than its own terminals. That alone fixed it for me.

What firmware version is the MPPT on? There were a couple of quirks in older versions around absorption timing that got patched.

Anyone else had this on a 48v system specifically? Curious whether it's more common at higher voltages.

@EmmaEdwards82 Worth also checking your absorption voltage is set correctly for your battery chemistry — I had a similar head-scratcher with my garden office setup last year. The MPPT was dropping to float early because the absorption time was set too short rather than a sensing issue.

Victron's default absorption time on some firmware versions is surprisingly conservative. In VictronConnect you can set it to use adaptive absorption or lock in a fixed duration — once I bumped mine up and let it run a proper full cycle, the batteries started actually reaching proper full charge.

Also worth logging a few days of data in VRM portal if you haven't already — the charge state graphs make the culprit pretty obvious once you see it plotted out.

@LindaLamb also worth logging it in VictronConnect — the history graph will snitch on your MPPT faster than your neighbour snitches about your panel tilt angle.

Great points all round. One thing I'd add — have a look at your tail current setting in VictronConnect. If it's set too high, the MPPT will decide the battery is "full" and drop to float prematurely, even if absorption time hasn't elapsed. On a 48v system with decent-sized battery bank, you want that tail current threshold fairly low relative to your bank capacity.

Also worth double-checking your absorption time isn't set to a fixed short duration — adaptive absorption is usually the better option as it adjusts based on how long the MPPT spent in bulk. @Mel1980 is spot on about the history graph too, the daily stats are brilliant for spotting patterns over several days rather than chasing a one-off event.

@WFS_Camper was clearly mid-sentence when the forum ate their reply 😂 — classic offgrid4less, even the website goes to float too early.

But yes, tail current is the one people miss. If your battery bank is large and the tail current threshold is set too high, the MPPT thinks "job done, brilliant"