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I have an RV with a 150 Ah battery bank and SureSine 300W 115V inverter. Due to space constraints, the inverter and the rest of the DC loads share about 6 ft length of wire to the batteries, but otherwise it’s a fairly typical setup.

The media center and speakers are running on the 12V and they pick up high pitched noise when the inverter is running, it gets worse the more AC loads I have.

The inverter probably already has bypass capacitors, but would it help if I added more? How do I choose the correct size? Would it help if I added a big ferrite bead on the positive rail going to the inverter? The peak current there is about 60A.

Also, does it make sense to filter the noise just at the media center as it uses a fraction of the power the inverter does?

Edit: I have a multimeter, but not much besides that to diagnose this.

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  • \$\begingroup\$ How do you know there is noise with just a multimeter? \$\endgroup\$
    – DSWG
    Commented Apr 22, 2018 at 22:04
  • \$\begingroup\$ I can hear it with my ears on the speakers when the inverter is on. \$\endgroup\$
    – Gunchars
    Commented Apr 22, 2018 at 22:05
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    \$\begingroup\$ Oh - you're talking about audio noise, not electrical noise? This could be due to vibrations, resonant frequencies between components, or some circuitry inside the inverter that you won't be able to access. Not sure if there is much you can do here besides filter caps as you've already self-suggested \$\endgroup\$
    – DSWG
    Commented Apr 22, 2018 at 22:11
  • \$\begingroup\$ Can you put a common mode choke around the cables and listen if that attenuated the noise? \$\endgroup\$
    – winny
    Commented Apr 23, 2018 at 6:08

3 Answers 3

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run individual leads from the batteries to the inverter use shielded cables ground the shields run these in metallic conduit ground the conduit put some large capacitors in parallel with the inverter dc feed and finaly if needed put the inverter in a Faraday cage a copper enclosure and ground this

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Your setup is similar to car audio so I would imagine they have a suitable solution to this problem. You can buy very large audio capacitors in the multiple farad range. Place one of these as close to the audio system as possible and see if that resolves your problem. If not you can put an inductor in front of this capacitor to create an LC filter.

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It turned out to be caused by a ground loop. I had mistakenly made two connections to the chassis when installing the inverter, one at the battery and another near the inverter. This caused the aluminum frame of the camper pick up quite a bit of EMI. There's still some noise so I'll try some of the suggestions here, but it's a tiny fraction of what it was.

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