Protecting my 12v RV Panel

Been thinking about this a lot lately after hearing about someone's catastrophic 5th-wheel failure — basically fried every 12v device they had. Sounds like an MPPT fault caused a voltage spike that wiped through the whole system.

Got me wondering about my own setup. Running a Victron SmartSolar 100/30 into two Fogstar Drift 100Ah lithium batteries, and I've never actually sat down and properly mapped out what would happen in a worst-case scenario. Bit of a worry tbh.

A few things I've been mulling over:

• Fusing between MPPT and battery — I've got one, but is it sized correctly to actually protect downstream devices or just the cabling?
• Overvoltage protection — if the MPPT goes rogue, is there anything stopping it from pushing way above 14.6v into the system?
• BMS as the last line of defence — mine will cut out on overvoltage, but by then damage could already be done to anything plugged in

I think the proper way to do this is a dedicated battery protect relay on the load side, but I've never actually fitted one. Been putting it off.

Has anyone had a partial or full system failure like this? Curious whether it was an MPPT fault, wiring issue, or something else entirely. Also wondering if anyone's running surge protectors on their 12v appliance feeds — feels a bit overkill but maybe it isn't?

Would love to hear how others have thought through their protection layers, especially if you're running lithium. Don't want to learn this lesson the hard way.

@VitoSolar — MPPT overvoltage faults are real but often overstated as a cause. More commonly it's a failed shunt regulator or a PWM controller mis-wired to a lithium bank.

Regardless of cause, the protection stack I'd recommend:

• Victron BMS with load disconnect output — cuts everything if cells go out of range
• Victron Battery Protect on the 12v distribution rail — takes the BMS signal cleanly
• Class T fuse at the battery terminal, not buried somewhere mid-run
• TVS diode array across sensitive devices if you're paranoid

On my narrowboat I run a Fogstar Drift 100Ah with its built-in BMS plus an external Victron BP-65. Two layers. The BMS handles chemistry-level protection, the BP handles load shedding.

Don't rely on a single device to do everything. Redundancy isn't overkill — it's just engineering.

@VitoSolar slap a Victron Battery Protect between your MPPT and your 12v panel — sorted, and it's roughly the price of one ruined 12v compressor fridge you'll be kicking yourself about later.

@GlenSimon the Battery Protect is decent but worth noting it's unidirectional — can't use it on circuits where you need two-way current flow (alternator charging into the same bus, for example). Caught me out on the boat before I read the small print properly.

Also worth considering a Victron Orion with proper voltage sensing if your setup's more complex.

@VitoSolar what's actually driving the 12v panel — is it a shared bus with your alternator or purely solar? Makes a difference to what protection makes sense. A simple TVS diode array on sensitive devices costs pennies and absorbs spikes before they fry anything, regardless of what else you fit upstream. Not a complete solution on its own but a useful belt-and-braces layer.

@ExBrickie makes a good point on the BP limitation — worth adding that for bidirectional circuits a Victron Orion or a dedicated relay-based disconnect is the better shout.

Also nobody's mentioned overvoltage protection at the device level — a decent TVS diode array or a crowbar circuit on critical loads gives you a last line of defence if everything upstream goes wrong. Relatively cheap insurance.

On my garden office setup I run a Fogstar battery with a solid BMS that handles OVP, plus a BP on the pure consumer circuits. Belt and braces.

Also double-check your MPPT's absorption/float settings are correct for your battery chemistry — a misconfigured Renogy unit caused a mate's issue, nothing exotic, just wrong voltage set point baking his AGMs slowly over months.

Great points from everyone so far. One thing I'd add — whatever protection route you go down, make sure you've got appropriately rated fusing as close to the battery as possible before anything else. A lot of folk focus on the downstream protection and overlook this fundamental step. Even with a Battery Protect or similar in place, a dead short anywhere in your cabling can cause a fire before any smart device has chance to react. The fuse is your last line of defence there.

Also worth checking your MPPT's absorption and float voltage settings are correctly configured for your battery chemistry — a misconfigured charger is often the root cause of these spike scenarios in the first place. Prevention beats cure. 🙂