Quieter fan for Multiplus II

Been meaning to post about this for a while. Running a Multiplus II 3000 in my motorhome and the fan noise has been driving me mad, especially when I'm trying to sleep and it decides to kick in at 2am during absorption.

Has anyone actually swapped the fan out on one of these? I know Victron won't love you for it, but it's not like it voids any warranty that's already expired.

From what I've dug around online, the stock fan seems to be a standard 12V DC unit — but I'd want to verify the exact voltage and connector before ordering anything. The concern is whether a quieter replacement moves enough air to keep temps sensible, particularly in summer. Last July mine was working hard and I'd rather not cook the inverter trying to be clever.

A few options I've seen mentioned:

• Noctua fans — obviously the gold standard for quiet, but need to check sizing and airflow specs match
• Arctic fans — cheaper, still decent static pressure
• Sticking with the stock fan but adding VictronConnect temperature profiles to manage when it spins up (limited but worth trying first)

I've already played with the ESS settings a bit to reduce how hard the unit works overnight, which has helped somewhat. But there are still nights where it just decides to run constantly.

Anyone in the UK actually done this mod? Curious whether the Multiplus II 3000 shares internals with the 5000 or if they're different fans entirely. Would be good to pool knowledge rather than everyone guessing individually.

@SteveWhite70 worth knowing the fan behaviour is actually configurable via VE.Configure. There's a Fan Operation setting where you can adjust the temperature threshold at which it kicks in. A lot of people don't realise the defaults are quite conservative.

Also worth checking your absorption/float timing — if it's hitting a charge cycle at 2am that's pushing heat, that's your culprit. On my narrowboat I shifted the bulk charge window to daytime hours using the scheduled charging feature in VE.Configure and the night-time fan events basically disappeared.

If it's genuinely running hot regardless, check your ventilation. I had mine in a poorly ventilated locker and the fan was constant. Added a simple passive vent and it dropped significantly.

Swapping the fan itself voids warranty and isn't straightforward on the MPII — I'd exhaust the software/thermal options first.

@ExSquaddie49 good shout on VE.Configure — worth adding that you can also set the temperature threshold for when the fan kicks in. Mine was running the fan way earlier than it needed to. Bumped the threshold up a bit and it made a noticeable difference overnight.

Also worth checking your load settings — if you're running loads that push it harder than needed it'll thermal up quicker. I reorganised some of my overnight draws in my van build and the fan barely spins up now.

One more thing — make sure it's got decent airflow around it. Mine was in a tight cupboard originally and that made everything worse.

@ExSquaddie49 @Brummie86 both making good points there. One thing worth adding — if you haven't already, check what's actually causing the thermal load in the first place. On my Multiplus II 5000 I found the fan was cycling aggressively at night because I had absorption charging set quite high (57.6V for my lithium bank) and it was pushing the unit hard. Dropping to a more conservative charge current overnight via a scheduled assistant made a significant difference before I even touched the fan settings.

Also worth physically checking the ventilation clearances — Victron's minimum is 10cm on all sides but in a motorhome install that's often compromised. Restricted airflow means it runs hotter, fan kicks in earlier, runs longer. Sometimes the fix is a small duct rather than reconfiguring the unit itself.

@SueThompson raises an important point about identifying the actual cause first.

One thing nobody's mentioned yet — load profile matters enormously here. In my garden office setup I found the fan was cycling on/off repeatedly during moderate loads, which turned out to be worse than just running continuously. Worth logging your AC loads and battery temps over a few days using a GX device or Cerbo if you have one — the data usually reveals whether it's thermal or something else entirely.

Also worth checking: is your Multiplus II physically well-ventilated? Mine was in a fairly enclosed compartment initially. Adding even modest airflow around the unit dropped fan activation frequency noticeably without touching any settings.

The VE.Configure route @ExSquaddie49 mentioned is valid, but I'd exhaust the physical/environmental checks before adjusting firmware behaviour — masking a symptom rather than solving it rarely ends well.

Really useful thread — following closely as I've got the same unit in my motorhome.

One thing I haven't seen mentioned: have you checked your battery voltage under load? I found my Multiplus was spinning the fan harder than expected because it was working overtime compensating for a slightly undercharged bank. Once I sorted the absorption/float settings properly in VE.Configure, the thermal load dropped noticeably.

Also worth asking — is the fan noise constant or does it ramp up suddenly? On mine it tends to be the latter, usually coinciding with the compressor fridge cycling. Might be worth logging with a Cerbo GX if you have one, to see exactly what's triggering it at 2am rather than guessing.

What's your battery chemistry? LiFePO4 or AGM? That might affect what settings people can usefully suggest.