Solar controller 75/15 always in float

So here's one that's been doing my head in for the past couple of weeks — thought I'd throw it out to the collective wisdom here.

I've been running a Victron SmartSolar 75/15 on my shepherd's hut setup since the spring. Paired it with a Fogstar 100Ah LiFePO4 and a single Renogy 175W panel mounted on the south-facing roof slope. All seemed grand at first.

Problem is, the controller jumps into float almost immediately after sunrise — we're talking 8am on a decent day, battery sitting at maybe 80% state of charge. It should be absolutely hammering away in bulk, but no. Straight to float, barely pulling 2-3A.

I've gone through the VictronConnect app settings more times than I care to admit. Absorption voltage, float voltage, battery type — all look sensible for lithium. The wiring's solid, connections tight.

My gut says it might be a misconfigured battery profile — possibly the algorithm is reading surface voltage from the lithium rather than true SoC, so it thinks the bank is full when it isn't. There's a known quirk with some LiFePO4 setups where the resting voltage fools the controller.

Has anyone else seen this with a 75/15 specifically? I know some folk on here have been through similar with van or cabin installs. Would love to know if a custom charge profile sorted it, or whether it needed something more drastic.

Worth mentioning — the hut is also where I'm experimenting with a small EV charging trickle setup, so reliable solar throughput genuinely matters rather than being purely academic!

@DaleVicky you've cut off mid-post but I'll take a guess at the classic symptom — controller sits in float almost immediately after sunrise even though the battery isn't actually full?

Had exactly this on my van build. Nine times out of ten it's one of these:

• Battery absorption voltage set too low — check your profile in VictronConnect matches your actual battery chemistry
• Tail current threshold — if it's set high, it'll drop to float prematurely
• Small panel relative to battery capacity — the current never really pushes hard enough to trigger a proper absorption cycle

What battery are you running? AGM, lithium, leisure lead-acid? And what are your absorption/float voltage settings currently showing in VictronConnect?

Also worth checking the history tab — it'll show your daily yield and whether absorption time is genuinely near zero.

@DaleVicky classic case of your battery already being full when the sun comes up — if you're not drawing much overnight, a healthy battery wakes up at 12.7-12.8V and the controller goes "job done, float it is" before you've even had your morning brew ☀️

@NaeClue has the most likely explanation covered, but there's another angle worth ruling out — battery voltage offset from a long cable run.

I had something eerily similar on my garden office setup. Victron was reading 13.8V at the controller terminals while the battery was actually sitting at 13.2V because I'd not accounted properly for voltage drop across the cable. Controller thought it was already in float territory before the real charging had even begun.

Worth grabbing a multimeter and measuring directly at the battery terminals while the controller is running. If there's a meaningful difference, your cable gauge is likely too light for the run length.

In VictronConnect you can also set a tail current threshold which helped me enormously — it tells the controller to only drop into float once absorption current has genuinely tapered off rather than relying solely on voltage.

@NaeClue and @JennyThomas57 have the obvious bases covered, so I'll add one that bites people constantly — parasitic voltage drop on the battery sense wires.

If your SmartSolar is doing voltage sensing via the VE.Direct connection or the battery terminals directly, any dodgy crimp or corroded connection between controller and battery will cause it to read a higher voltage than reality. Controller thinks "brilliant, we're at 14.2V, float time!" — battery is actually sat at 12.8V having a sulk.

Stick a decent multimeter directly across your battery terminals and compare it to what VictronConnect reports in real-time. If there's more than ~0.1V discrepancy, you've found your culprit.

Also worth checking: what's your float voltage set to? Default on the 75/15 is 13.5V for lead-acid — if someone's bumped it up toward absorption territory, it'll tip into float at the slightest provocation.