First Look: The New Victron MultiPlus-II 4K 2x120 for RV Power Systems
We’ve been waiting on this one for a while.
The new Victron MultiPlus-II 4K 2x120 is finally here, and we wanted to get it out of the box, put it next to the 3K, and see what actually changed.
For RV owners, the biggest difference is pretty simple: more power from a single inverter without taking up a whole lot more space.
Why the 4K is a big deal for RVs
A typical 30-amp RV service gives you up to 3,600 watts of power.
The MultiPlus-II 3000VA has been one of the most common choices for RV systems, but when it’s actually inverting, you’re generally looking at around 2,400 watts of continuous output.
The new 4K gets a lot closer to that full 30-amp number.
Depending on which Victron documentation you look at, the output is listed around 3,400 watts, while the data label on the unit shows 3,600 watts at room temperature.
Either way, that’s a pretty big jump over the 3K.
You’re gaining roughly 1,000 to 1,200 watts of inverter output from a single unit, which could make a big difference in larger RV systems.
It Really Isn’t Much Bigger
One of the first things we wanted to know was how much larger the new 4K would be.
Surprisingly, not much.
The MultiPlus-II 3K measures about 23 x 11 x 6 inches, while the new 4K measures 25.6 x 11 x 6.5 inches.
So the 4K is roughly 2.8 inches longer overall, the same width, and only about two-thirds of an inch deeper. You're getting considerably more inverter capacity without having to make room for a dramatically larger piece of equipment.
Victron Stepped Up the Fan Cooling
One of the more interesting changes we found is the cooling setup. The older MultiPlus-II 3K uses a single fan that moves around 110 CFM, while the new 4K uses two fans that each move about 130 CFM, giving the new inverter roughly 260 CFM of total airflow.
That extra airflow matters because more inverter output also means more heat to manage. In an RV installation, especially when the inverter is mounted inside a tight compartment, being able to move that heat out efficiently can make a big difference.
We haven’t put the 4K through a full load test yet, but based on the cooling setup alone, it looks like Victron made a meaningful improvement here.
Inside, it still looks familiar
Once we took the covers off, a lot of the layout looked very similar to the 3K.
The AC and DC connections are still set up much the same way, which is good news for installers who are already familiar with the MultiPlus-II.
We would have liked to see a little more room around the cable entry points, especially since the larger inverter calls for heavier battery cabling.
That’s something installers will still need to plan around.
Zero-load power use
The new inverter does use a little more power while sitting idle.
The 3K is around 15 watts with no load.
The new 4K is around 18 watts.
That’s not a huge difference considering how much more inverter capacity you’re getting.
What Does 2x120 Actually Mean?
Both of these inverters are 2x120 models, which makes them especially useful in North American RVs. When you’re plugged into a standard 50-amp 120/240V shore power connection, the MultiPlus-II passes both incoming legs through, so the RV still has access to 120V on each leg and 240V between them.
When you switch to battery power, however, the inverter produces 120V single-phase power and internally connects L1 and L2 together. That means both sides of the RV’s electrical panel still receive 120V, but there is no 240V available between the two legs while inverting.
For most RVs, that works just fine because nearly everything in the coach is designed to run on 120V.
Could the 4K replace the 3K?
For a lot of RV systems, we think it probably will.
The MultiPlus-II 3K is still a great inverter, but the 4K gives you significantly more output, much more airflow, and only a small increase in physical size.
That makes it a really attractive option for anyone who wants more power without jumping into a dual-inverter setup.
Right now, the unit we’re looking at is the 12V version. There isn’t currently a 24V or 48V version of this exact model for us to compare.
Next up: putting it under load
This first look tells us a lot, but the real question is how it performs when we actually push it.
Next, we’re going to put the MultiPlus-II 4K under load and see whether it can sustain that 3,600-watt output, how hot it gets, and how it compares directly with the 3K.
That’s the test we’re really looking forward to.
If you’re planning an RV battery, inverter, or solar upgrade and you’re not sure what makes sense for your rig, head to BigBeardBattery.com and fill out our System Design Form. We’ll talk through what you’re trying to power and help you build a system around the way you actually use your RV.
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