Occasional #38 input shutdown

Been having something similar crop up on my Victron Multiplus II 3kVA at the cabin and wondered if anyone else has seen this.

Mine's a single unit rather than a parallel setup, fed by a pair of 200W panels through a SmartSolar MPPT 100/30. Battery bank is 200Ah of Fogstar Drift LiFePO4. The whole thing sits in a fairly small insulated enclosure on the south wall.

Twice this summer — both times on properly sunny days, which in Scotland is practically a calendar event worth noting — the unit threw error #38 and shut the input down. Each time it recovered on its own after 10-15 minutes without me touching anything.

My working theory is thermal. The enclosure probably isn't getting enough airflow on the days when the sun is actually hammering the south-facing wall and the inverter is working hard. Bit of a perfect storm situation.

A few things I'm curious about from people who've dealt with this:

• Is #38 specifically an overtemperature input shutdown or is it more nuanced than that?
• Would adding a small 12V fan triggered by a thermostat inside the enclosure be worth doing, or is relocating the unit more sensible?
• Anyone using external temperature monitoring through the Victron ecosystem to catch this before it shuts down?

I've had a look through the Victron documentation and it's not exactly chatty on what triggers #38 specifically versus other thermal codes.

Probably not a crisis given how rarely it's happened, but I'd rather get ahead of it before next summer rolls around.

Hey @RetiredChef71, welcome to the forum! That error 38 is an input shutdown due to excessive DC ripple on the battery side — Victron throws it when the ripple voltage exceeds acceptable limits.

With a pair of 200W panels feeding a single Multiplus II, my first suspicion would be your battery connections. Loose terminals or undersized cabling between the batteries and the inverter are classic culprits — the ripple spikes under load and trips the protection.

Worth checking your battery interconnects are properly torqued and your DC cable run isn't too long. Also, are your batteries in good nick? Aging cells struggle to absorb ripple effectively.

Have a look in VictronConnect at your battery voltage graph when it happens — if you see sharp dips, that's pointing straight at your wiring or battery health rather than the inverter itself.

@RetiredChef71 Error 38 is basically the Multiplus saying "sort your connections out before I do something we'll both regret."

Classic culprits in my experience:

• Loose or undersized DC cabling — ripple loves a dodgy connection
• Battery BMS throttling output mid-draw, causing voltage to s

@RetiredChef71 had this exact issue on my static caravan setup last summer. Turned out my battery terminals were slightly loose — looked fine visually but had enough resistance to cause ripple under load. Worth torquing everything down properly with a calibrated wrench rather than just hand-tight.

Also check your busbar connections if you're running one. Mine were fine but I've seen others on here where the crimps on the DC cables were the culprit — fine at low loads but causing grief when the Multiplus ramped up.

One other thing — what firmware are you running on the Multiplus? Victron pushed an update a while back that tweaked the ripple detection sensitivity. Might be worth checking via VictronConnect if you're on an older version before assuming it's a hardware fault.

Worth adding — check your fuse holder too. Had a dodgy ANL fuse holder on my shepherd's hut setup causing similar grief. Looked fine visually but was creating resistance under load. Swapped it for a proper Blue Sea unit and the ripple readings dropped right off.

Also if you're running Victron Connect, pull up the advanced tab while it's actually happening — you can see the DC ripple voltage in real time. Makes it much easier to pin down whether it's connections, the batteries themselves, or something else entirely.

What cells are you running in those batteries? Some cheaper LiFePO4 packs struggle to deliver clean current under sudden load spikes, which can trigger #38 even with solid connections.

Ran into something similar on my motorhome build a couple of years back — took me far longer than I'd like to admit to track down the culprit. Turned out to be the crimped lugs on the battery-to-busbar cables. Looked absolutely fine visually, but when I used a proper clamp meter during load I could see a voltage drop that had no business being there. Replaced the lugs with decent copper ones and re-crimped with a hydraulic tool rather than the cheap ratchet crimper I'd been using — problem vanished immediately.

@RetiredChef71 if you haven't already, it's worth doing a proper volt-drop test across every connection point under load rather than just eyeballing things. The Multiplus is quite sensitive to anything that looks like an unstable supply.