Anyone else had grief with a Victron SmartSolar 100/20 dropping to float too early on a 200Ah LiFePO4?

Set mine up last week — 2x 100W panels in series feeding a 200Ah LiFePO4 leisure battery. I've got the charge profile set to 14.2V absorb, 30 min absorb time, 13.5V float, which seems pretty standard from what I've read. Problem is, on a decent sunny day it's hitting absorb voltage within about 20 minutes and then dropping straight to float before the battery's anywhere near full. SOC on my Victron BMV-712 is showing maybe 70-75% when it transitions.

I know LiFePO4 has a very flat voltage curve and the MPPT can't really tell the difference between 50% and 90% SOC just from voltage alone. But I'm wondering if I've got the absorb time set too short, or whether I should be using the tail current feature to hold absorb until the charge current drops below a certain threshold. I've had a look at the VictronConnect app and there's a "tail current" option but I'm not sure what value to set it at for a 200Ah pack.

Has anyone dialled this in properly on a similar setup? What absorb time or tail current figure are you running? Bit wary of just guessing and either undercharging or cooking the cells.

Bump your absorb time to at least 2 hours mate — 30 mins on a 200Ah bank is like trying to fill a bath with a thimble, the Victron barely gets going before it's already clocking off for a nap 🛁

@FET_King 30 minutes absorb on a 200Ah bank is doing basically nothing — my static van setup taught me that the hard way when I kept wondering why my Fogstar 200Ah was perpetually grumpy by evening.

Hey @FET_King — just to add a slightly different angle to what @Chopper54 and @KentExplorer have said, it's worth checking whether your MPPT is actually reaching 14.2V before the absorb timer kicks in. On a cloudy day or with any shade, mine was technically "in absorb" but only delivering 13.8V, so the timer ran its 30 mins on a half-baked charge.

Also worth enabling the BatterySense or at least checking your battery temp — LiFePO4 can be fussy and some controllers back off absorption prematurely if temperature compensation is miscalculated for lithium chemistry. Make sure your temp compensation is set to zero for LiFePO4 in VictronConnect. Might explain the early float behaviour even once you've sorted the timer. 😊

Great points from everyone already on the absorb time. One thing nobody's mentioned yet — have you checked your tail current setting? On LiFePO4 the battery is essentially full when current drops to around 2-5% of capacity, so for your 200Ah bank that's roughly 4-10A. If your controller is switching to float purely on a timer rather than watching tail current, you'll always get inconsistent results regardless of absorb duration. The SmartSolar 100/20 does support tail current termination — worth digging into the VictronConnect app under the expert charge settings. Also double-check your wiring for any voltage drop between controller and battery, as the MPPT could be "seeing" a higher voltage than what's actually reaching the cells and bailing out early. A proper sense wire directly at the battery terminals makes a big difference. 🙂