Anyone had issues with a Victron SmartSolar 100/30 dropping to float too early on cloudy days?

Just picked up a second-hand Victron SmartSolar MPPT 100/30 for my van build and I'm seeing something a bit odd. On overcast days the controller seems to jump into float mode after only an hour or so of absorption, even though the battery (a 100Ah Lithium LiFePO4 from Fogstar) is sitting at around 80% according to the Victron Battery Sense. I've got a single 200W panel on the roof and the absorption voltage is set to 14.2V with float at 13.5V.

From what I understand, the SmartSolar uses a combination of voltage and a tail current threshold to decide when absorption is done. My suspicion is that on a grey day the panel just can't push enough current to keep the voltage up properly, so the controller interprets the low current as the battery being full when it clearly isn't. Does that sound right to people with more experience of these units?

Has anyone adjusted the tail current settings in VictronConnect to fix something like this? I can see there's an option in the expert settings but I don't want to go fiddling blindly. Any advice on sensible values for a 100Ah LiFePO4 would be really helpful — I've seen people mention anywhere between 2A and 10A as a tail current cutoff and I genuinely don't know where to start.

Had this exact issue with mine on the shepherd's hut setup last winter. Nine times out of ten it's the absorption voltage threshold being hit too quickly because the battery wasn't as discharged as you thought — so the controller thinks it's done.

Worth checking a few things:

• What battery type have you got it set to? If it's on a preset rather than custom, the absorption voltage might be slightly off
• Check your absorption time setting — mine was defaulting to a very short adaptive period
• Also look at the tail current setting in VictronConnect, lowering it means it stays in absorption longer before dropping to float

The 100/30 is solid kit but the default profiles aren't always ideal for non-standard batteries. What chemistry are you running?

@AndyReid what battery type have you got it set to? Classic mistake when buying second-hand — previous owner may have fiddled with the charge profile and left it configured for something completely different to what you're running.

Also worth checking the tail current setting in the VictronConnect app. If that's set too high, the MPPT thinks the battery's full when it's nowhere near. On a cloudy day your panels are already pushing less current, so it hits that threshold almost immediately and scarpers off to float like it's done a hard day's work.

What batteries are you running — AGM, lithium, wet cell? Makes a big difference to what the correct settings should be. If you've got lithium in there and it's still on a gel profile you might have bigger problems than just float timing tbh.

Hey @AndyReid, worth checking your absorption time settings as well as what @TerryScott72 and @Robbo are getting at. The SmartSolar has an adaptive absorption algorithm that calculates absorption time based on the previous night's discharge — if the batteries weren't heavily discharged it'll shorten absorption considerably. On a cloudy day with limited current coming in, the controller can sometimes interpret the voltage behaviour oddly and cut absorption short.

Try connecting via the VictronConnect app and have a look at the history tab — you'll be able to see exactly what's happening across charge cycles. Also worth checking whether BatteryLife is enabled, as that can affect behaviour too. What capacity and chemistry are your batteries? That'll help narrow it down further.

Great points from @TerryScott72, @Robbo and @Brian1975 already. One thing nobody's mentioned yet — on the SmartSolar you can check the history logs in the VictronConnect app. Have a look at the "absorbed Ah" figure for those cloudy days. If it's reaching float early, the controller may be using the tail current setting as its exit condition rather than a fixed absorption time. On a cloudy day with low charge current, the tail current threshold can be hit surprisingly quickly, making the unit think the battery is full when it isn't.

Worth connecting via Bluetooth and checking what your tail current is set to — if it's been left at a higher percentage by the previous owner that'd explain exactly what you're seeing. You can adjust this in the expert settings within the app. What capacity are your batteries roughly?

Good shout from everyone above. One thing worth adding — on cloudy days your panels are putting out much lower current, so if the controller reaches the absorption voltage threshold (even briefly due to a surface charge) it can start the absorption timer. With weak solar input the battery might not actually be accepting much current, so the controller thinks it's satisfied and drops to float sooner than you'd expect.

Have a look at the tail current setting in VictronConnect — that's the amperage threshold below which the controller considers absorption complete. On a 100/30 it defaults fairly low, and on a dull day your charge current might barely exceed it. Bumping that setting up slightly can help force a proper absorption cycle before it transitions. Worth connecting via Bluetooth and having a poke around in the expert settings. What size battery are you running?

Following on from what @Squib19 said about lower current on cloudy days — this is actually what catches a lot of people out. The SmartSolar uses a tail current threshold to decide when absorption is "done" and it switches to float. If your battery is already reasonably charged and the panel output is already low due to cloud, that tail current figure can be hit really quickly.

Worth checking in the VictronConnect app what your tail current is set to. Default is something like 2A I think — might be worth bumping it down slightly.

I had a similar head-scratcher with my garden office setup before I realised the battery was basically never getting a proper full charge on grey days. Took ages to spot it.