Two Victron MPPT Failures in 3 Months – What Could Be Causing This?

So I'm at my wit's end with this one and hoping someone here has seen something similar.

Running a modest setup on my shepherd's hut — Victron SmartSolar 100/30 feeding a small Fogstar Drift lithium bank. First controller packed in back in February, which I put down to bad luck. Victron warranty replacement arrived promptly enough, but now that second unit has thrown the towel in too, barely eight weeks later.

Both times the symptoms were identical: dropped into a strange absorption loop, then just... stopped communicating via Bluetooth. Dead as a doornail.

The hut is parked on fairly exposed ground in the Pennines, so weather is a factor I can't ignore. But these units are supposed to handle the elements, aren't they? I've got the MPPT mounted inside a vented enclosure on the internal wall, so it's not taking direct rain.

A few things I'm wondering about:

• Could voltage spikes from the panels be frying something internally? I'm running two 200W panels in series, well within spec on paper
• Is there any known issue with the 100/30 batch from late 2025?
• Could a dodgy earth somewhere be causing grief repeatedly?

The installation was done properly — crimped lugs, fused correctly, cable sizing checked — so I don't think it's a wiring blunder on my end, but I'm starting to second-guess everything.

Has anyone else had repeat MPPT failures rather than a one-off? And what was the culprit? Really don't want to shell out again if the root cause is still sitting there waiting to kill a third unit.

@SteveBurns99 what's your wiring like between the panels and the MPPT? Two failures in three months on Victron kit — which is normally bulletproof — makes me suspect something upstream rather than the units themselves.

Specifically:

• Are your panels wired in series? If Voc spikes above 100V (even briefly in cold morning sun) that'll fry the controller
• Any loose MC4 connections? Arcing can send voltage spikes through that'll kill the electronics
• Is there any chance of reverse polarity happening during installation?

I had a similar head-scratching moment on my boat setup before realising my panel Voc was borderline — cold mornings pushed it over the limit. Worth checking your panels' cold-weather Voc figures against the 100V ceiling on the 100/30.

What panels are you running and how are they configured?

Check your panel Voc on a cold, clear morning — if those panels are wired anywhere near 100V open-circuit, one frosty Welsh dawn will spike right over the controller's limit and fry it before you've even boiled the kettle.

@OffGridGeek has already nailed the most likely culprit tbh.

One thing worth adding — check your cable runs for any chafing or exposed conductors, especially if the hut moves at all or you've got cables passing through any edges. A partial short on the PV side can cause all sorts of grief.

Also worth asking: are both failures the same symptoms? If it's dying with a specific fault code, pull that from VictronConnect history before you RMA it — that'll tell you a lot more than guessing.

Final thought — is your battery BMS cutting out abruptly under load? Victron MPPTs don't love sudden open-circuit on the output side repeatedly. If the Fogstar BMS is tripping and the MPPT sees it as a fault repeatedly, long-term that's not great.

@OffGridGeek and @Wez1961 have covered the Voc issue well, so I'll add something nobody's mentioned yet.

Two failures in quick succession strongly suggests a wiring fault introducing voltage spikes rather than sustained overvoltage. Loose MC4 connectors are notorious for this — they arc under load, generating transient spikes that can exceed the MPPT's input protection rating instantaneously, even when your steady-state Voc looks fine.

With my narrowboat setup I had something similar traced to a poorly crimped MC4 that only played up when the cable flexed in wind.

Check every MC4 joint with a firm tug test and ideally a clamp meter looking for unexpected current drop. Also worth fitting a Victron-compatible surge protection device on the PV input — Victron do recommend this in higher-risk installations and it's cheap insurance compared to another replacement unit.