Inverter making more noise

2Brooktrout · August 2020

My Magnum MSH-4000RE has been working well for about a year. It is located in the basement and It was pretty quiet until lately when I can hear the "transformer" hum whenever it is producing more than about 100 watts. It is louder as more power is produced. I checked for loose mounting but everything seems tight. I have not opened the case to explore inside. Is there something I should check or just wait and see what happens? It still has a year or so of warranty.

BB. · August 2020

I guess you have a pure sine wave inverter... That is good. It sometimes happens that MSW (modified square/sine wave) inverters can have a 120 Hz rattle from the (sort of) square wave of the AC output (sometimes lights, other appliances kind of "ring" too). The sharp "edges" of the MSW wave form can cause wiring/transformers and sheet metal to buzz.

If the noise is not from a fan (bearings, a cable that "bent near the fan blades", possibly a dirty vent/air filter)... Then it is probably from the transformer windings. There is usually not much you can/or should do to quiet that down. You can also look at the heavy cabling to/from the transformer--Sometimes they tie the wiring together to reduce "rattle" too.

If you do open it up, about the only things you could "fix" would be if a power transistor became loose and was buzzing against a heat sink (tighten the screw, double check the clip if used, etc.).

If the "buzz" is getting annoyingly loud, you might wish to contact the store/Magnum support and see about a replacement. Otherwise, just continue to use it.

Good luck,
-Bill "no great insight here" B.

RCinFLA · August 2020

It does not sound normal. It would be worth a call to Magnum to get their opinion.

From your description it sounds like low freq buzz. It is critical that the transformer does not build up a DC net bias on the magnetic core. If one or more of the parallel MOSFET's in primary side bridge goes bad it can create an offset build up in core bias which can saturate core that could sound like a low freq buzz. It puts additional stress on the good MOSFET's as their current shoots up at onset of transformer saturation.

I don't know what your diagnostic equipment capability is but at minimum I would measure the AC output voltage as you increase the loading on the inverter. Stop increasing loading if buzz get really loud. Hopefully there is safety sensing to prevent additional damage. It would be better if you have a scope to look at the AC output while you increase the load. Look for onset of clipping or distortion on the sinewave as you increase load.

Other thing to pay attention to is battery current, assuming you have a battery monitor. If you compute the DC power for a given AC loading does it match expectation based on inverter efficiency at the particular AC power loading level. If efficiency starts to drop significantly at a midrange loading it is a sure sign something is not right.

mike95490 · August 2020

My XW inverter buzzes louder with heavier loads. For me that's normal from day 1.

Inverter making more noise

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