250/85 high voltage

Seen something similar crop up with my Victron MPPT — not the same model but worth chucking in here.

Had a stretch last summer where my 48V system was sitting rock solid at 52.2V across everything except the MPPT readout, which was showing nearly 3V higher than the rest of the kit. Spent ages convinced my Fogstar cells were playing up before I twigged it was a measurement/calibration issue on the controller itself rather than an actual voltage discrepancy.

Few things worth checking if you're seeing this:

• Wiring resistance between the controller and battery terminals — even a small drop (or rise) can skew the readings badly
• Firmware — Victron pushed an update a while back that sorted some voltage sensing oddities on certain MPPT units
• VE.Direct or Bluetooth readout vs actual terminal voltage — sometimes the displayed figure is the duff one, not the real output

If your Pylontechs are genuinely seeing 55.7V when full that's a different problem entirely and I'd be pulling the controller out sharpish. Pylontech's upper limit isn't something you want to mess with.

Is the 55.7V showing on the controller's own display, or are you measuring it at the terminals with a multimeter? That distinction matters a lot here.

Anyone else had calibration drift on older MPPTs? Curious whether this is more common than people realise on units that are 3+ years old and seeing daily cycle use.

@MarineGaz that's interesting — 52.2V on a 48V system is pretty normal float territory so I wouldn't read too much into that on its own. The "250/85" in the thread title is the MPPT model though, so worth checking if you're seeing that high voltage flag specifically.

What's your absorption set to? If your battery temp compensation is enabled and it's a warm day, the controller can sometimes push a bit higher than you'd expect. Also worth double-checking the battery voltage sense wires if you've got remote sensing enabled — a dodgy connection there can cause the controller to overcompensate.

Have you checked the VictronConnect history tab? It'll show any overvoltage events logged with timestamps which makes tracking it down much easier.

@Curly90 is right that 52.2V is nothing to panic about, but context matters a lot here. Last winter I had my garden office system doing something similar — sitting at what looked like a perfectly reasonable voltage but the MPPT was quietly refusing to push any meaningful current through. Turned out my Fogstar cells had drifted slightly out of balance and the BMS was essentially throttling everything as a precaution. The voltage looked fine on the surface but the behaviour underneath told a different story. Worth pulling up your history graph in VictronConnect and checking whether charge current dropped off around the same time — that pattern is usually far more revealing than the voltage reading alone.

@MarineGaz worth checking what your absorption setpoint is actually doing in practice. On my motorhome setup I caught my Victron MPPT creeping into "high voltage" alerts not because of a genuine overvoltage event but because the battery temp compensation was pushing the charge voltage up unexpectedly during cold mornings.

If you're running Fogstar or similar lithium cells, double-check your BMS cutoff sits above whatever the MPPT ceiling is — there shouldn't be a clash, but I've seen sloppy preset profiles cause nuisance trips.

Also worth pulling the history log in VictronConnect rather than just eyeballing live voltage — the logged peak values can tell a different story to what you think you're seeing.

@MarineGaz one thing nobody's mentioned yet — have you checked whether your MPPT is actually hitting absorption at all before dropping to float? Sometimes if solar input is modest relative to battery capacity, the controller never quite reaches the absorption voltage threshold and just idles along at whatever it's settled on.

I had this on my shed system last spring — looked perfectly stable on the face of it, but the batteries were chronically undercharged because absorption was being skipped entirely. Worth pulling the history log off the VictronConnect app if you haven't already, as it'll show you exactly what charge states it's cycling through day to day.

@SamReid raises a good point about whether absorption is actually being reached. Related question for the thread — has anyone looked at whether the PV array voltage is the limiting factor here rather than the charge setpoints themselves?

On my garden office setup I noticed my MPPT was occasionally throttling back before absorption because the Voc on cold mornings was pushing close to the controller's input ceiling. Could that be masking what's actually happening at the battery end?

@MarineGaz what's your array configuration — series strings or parallel? And what's the open-circuit voltage when temps drop overnight?