question

I have a Multiplus-II in the basement directly below our family room. The door to the basement is in the corner of the family room and is usually open. The Multiplus can make a sort of brief "pulsing" noise when charging intermittently or when an intermittent load is placed on it. When I run a 1500-watt coffee machine, after the tank is up to temp, it "pulses" the heating for about one second every 10 seconds. When the Multiplus is inverting, the sound is more consistent and could be audible at the top of the stairs if the rest of the house were quiet and I was listening for it.

But ordinarily, the sound is not audible anywhere upstairs even with the basement door open. I did have a sound issue with a Multiplus Compact mounted to a plywood board in my RV. The "hum" from the Compact would resonate on the plywood and amplify the sound which was easily audible when the surrounding noise levels were lower.

I do believe the method I used to mount the Multiplus-II in the basement makes a significant difference. I used concrete screws to attach a 3/4" plywood board to the foundation wall, then used more concrete screws to attach a 1/4" fiber backing board (the kind used to underlay tile) to and through the plywood into the foundation wall. I believe this combination of mounting boards and the security of the screws into the concrete completely inhibit any resonance.

Summing up, the Multiplus-II is not normally audible at all upstairs. But if the surroundings are very quiet, and you're listening for it, and it's cycling the inverter or charger on and off, I might be able to hear it. If I'm down in the basement, it is noticeable all the time, but not to the point of annoyance.

Multi Ii 3kw parallel to the grid.

Transformer hums louder under load Vent kicks in under load ≥500 W or so.

It's in a storeroom. Simple wooden door hardly notice outside,

But it sits on a detached studwall To prevent noise transmission when fixing to a normal wall some rubber fixings will help