Mpp solar inverter stops connecting pv panels

Had this exact drama on my narrowboat last summer — MPP Solar units can be proper diva when it comes to PV input, usually throws a wobbly if the open-circuit voltage creeps too high on a warm day or the panels are wired in a config it's not keen on.

Few things worth checking:

• VOC on your panels — are you running them in series? MPP Solar inverters have a surprisingly low PV input ceiling compared to what you'd expect, easy to accidentally fry the MPPT stage
• Firmware — the older versions had a known gremlin where it'd just stop recognising PV input after a certain number of charge cycles, updated mine and it sorted itself right out
• Wiring connections at the PV terminals — vibration on a boat absolutely murders these, but even on a static install a loose crimp will cause exactly this symptom

Worth grabbing a multimeter and checking you're actually getting voltage at the inverter terminals rather than just at the panels, because you'd be amazed how often it's just a corroded MC4 connector playing silly beggars.

If it's genuinely the unit giving up the ghost, honestly might be worth jumping ship (no pun intended) to a Victron — the support and community knowledge is miles better and they don't just randomly decide PV panels don't exist anymore.

What panels and config are you running? Might help narrow it down.

@MarineKaren interesting you mention the OC voltage thing — I've had the opposite problem in my tiny house setup where the panels weren't producing enough voltage on overcast days to trigger the MPPT threshold.

Worth checking a few things:

• What's your actual panel configuration? Series vs parallel matters massively here
• Have you checked the PV input voltage range in the MPP unit's settings? Some models have a minimum threshold around 60-120V depending on firmware
• Is the fault consistent or intermittent?

I'm running Victron kit now after similar frustrations, but I know MPP Solar units can be fussy about the voltage "window" — too high or too low and they just refuse to connect.

Have you tried logging the voltage at the moment it drops out? A cheap multimeter timed with the fault would at least narrow it down.

@MarineKaren worth checking the actual Voc at the combiner box rather than trusting the datasheet figures — panels in cold morning air on a narrowboat can spike well above rated Voc, and MPP Solar's MPPT input ceiling is not exactly generous at 145V on most models.

Classic culprit: too many panels in series because someone (not naming names, but I've been that someone) thought "ah, it'll be fine in British weather." Spoiler: it won't be fine.

Run the numbers with a proper temperature-corrected Voc calculation using your lowest expected temperature — PVWatts or even a back-of-envelope using the panel's voltage temperature coefficient will save you a world of pain.

If reconfiguring series/parallel strings isn't an option, a Victron SmartSolar handles wider input ranges far more gracefully.

@OldSailor makes a fair point about measuring at the combiner, but I'd also pull the PV input fuse and check whether the MPP Solar's internal MPPT input capacitors have gone leaky — I've seen this on a couple of these units where the tracker just refuses to latch onto the array properly at startup. Mine on the narrowboat did exactly this; swapped the unit and the problem vanished immediately.

Also worth checking: is the PV wiring running parallel to your AC cables anywhere? Induced noise on the input can confuse the MPPT logic on cheaper units. MPP Solar aren't exactly Victron when it comes to interference rejection. Run a temporary test lead directly from the panels and see if behaviour changes — quick diagnostic before you start chasing ghosts.

@OffGridTel good shout on the fuse, though I'd go one further — with MPP Solar units specifically, the PV input MOSFET can develop a high-resistance fault that shows perfectly fine on a multimeter under no-load conditions but collapses the moment current flows. Had something similar on the shepherd's hut build; panels measured fine, wiring checked out, but under actual charging conditions the voltage at the inverter terminals was sagging badly.

Worth logging the PV input voltage and current simultaneously using something like a Victron MPPT in monitor-only mode if you have one spare, or even a basic DC clamp meter. If voltage drops disproportionately once current starts flowing, suspect the internal MOSFET or the PV input capacitors rather than anything upstream. MPP Solar spares are available but the repair documentation is essentially non-existent without reverse-engineering it yourself.