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

Had this exact issue last summer with my 100/30. Kept hitting float around midday even though the batteries were nowhere near full — Fogstar 100Ah LiFePO4, so I could actually see the state of charge in the app and it was lying.

Turned out my absorption voltage was set slightly low for the battery's spec. Bumped it up from 14.2V to 14.4V and the problem mostly sorted itself. Worth double-checking your charge profile against your actual battery datasheet rather than trusting whatever preset you're using.

Few other things worth checking:

• Battery temp sensor — if Victron thinks the battery is warm it'll back off early. Mine was reading a few degrees high because the sensor was near a heat source
• Tail current setting — if this is too high it'll drop to float before the battery's properly topped up
• Wiring voltage drop — controller thinks voltage is higher than it actually is at the battery terminals

What battery are you running? Makes a big difference whether this is a genuine issue or just the controller doing what it's supposed to for your chemistry.

Also — are you on the latest firmware? There was a dodgy version a while back that caused weird MPPT behaviour. VictronConnect makes it dead easy to update.

What does your VRM dashboard show for absorption time? If it's cutting out after under an hour something's definitely off.

@SolarTrevor had exactly this with my setup at the cabin last year. Worth checking your absorption voltage threshold in VictronConnect — mine was set too low (leftover from a AGM profile someone had flashed on it previously).

Also, are you using the built-in BMS reporting or an external shunt? My Fogstar's BMS was sending dodgy voltage spikes over the wire which the MPPT was reading as "full" and bailing out early.

Few things to try:

• Set a fixed absorption time rather than adaptive
• Double-check your tail current setting (should be ~2% of capacity for LiFePO4)
• Firmware update if you haven't already

The Victron community forum has a cracking thread on LiFePO4 profiles specifically — saved me hours of head-scratching.

@SolarTrevor I had something similar with my static caravan setup — turned out my battery temperature sensor wasn't seated properly, so the MPPT was getting false high readings and assuming the batteries were warmer than they actually were. That caused it to throttle back absorption time way too early.

Worth checking if you're using the VE.Direct connection and VictronConnect app to log the actual charge cycle data — you can see exactly when it transitions and why. The history tab on mine showed the absorption time was barely hitting 10 minutes before dropping to float.

Also — what have you set for your absorption time minimum in the advanced settings? Out of the box defaults for LiFePO4 profiles can be a bit conservative on some firmware versions.

@SolarTrevor this happened to me on the shepherd's hut build — worth checking your tail current setting in VictronConnect. By default it's often set at something like 4% of battery capacity, which on a 100Ah bank can trigger float prematurely, especially if your panel wattage is modest and natural current drop happens quickly around midday.

I dropped mine to 1-2% and it made a big difference. You'll find it under the battery settings in VictronConnect — it's sometimes buried depending on your firmware version.

Also double-check your bulk/absorption voltage is actually set correctly for LiFePO4 — factory defaults are sometimes still set for AGM out of the box.

@SolarTrevor I'd also look at your absorption time setting in VictronConnect — if it's set to a fixed duration rather than adaptive, it can cut absorption short and tip straight into float before the batteries have had a chance to properly fill. Worth switching to adaptive if you haven't already, as it uses the tail current to decide when absorption is actually done rather than just counting down a timer.

Also worth double-checking your battery capacity setting is correct — if the MPPT thinks you've got a smaller bank than you actually have, it'll calculate everything accordingly and you'll keep seeing premature float. Sounds obvious but it catches people out more than you'd think!