EMI/RF electrical noise from Mitsubishi mini-splits

allenm

Has anyone here dealt with the EMI/RF electrical noise the inverters for variable speed compressors put out? We have a Mitsubishi Hyper Heat MUZ-FS06NAH-U1 and a MUZ-FS18NAH-U1. Those are the outdoor units where the inverters are located.

They completely wipe out the AM broadcast radio band, as well as some of my amateur radio bands. FM is not affected at all.

The only way I have to eliminate the noise is flipping off their circuit breakers in the AC service panel.

ratio

They have several EMI filters inside. I would imagine that they meet the FCC requirements, so maybe they are underperforming. A basic schematic can be found by searching for your model number at mylinkdrive.com or trane.mylinkdrive.com, depending on branding. Mitsubishi tech support seems to be willing to talk to homeowners as well in my experience.

As I understand it, most (all?) 'inverter driven' compressors aren't three phase compressors with a VFD, but rather large BLDC motors, meaning they get driven with pulsed DC from H bridges so fast rising edges are the norm.

Jamie Hall

You may find you need to put ferrite chokes on the power feeds to the units, although the internal filters should do the job, they may not be up to it -- particularly on your amateur bands, where your signal strengths are probably not that high anyway. Your problem is not unique. I have found that the harmonics on the power lines cause a good deal of high harmonic noise in high fidelity sound systems unless power conditioners are used (which are, of course, really just big chokes).

allenm

I have noticed a Mitsubishi R61-020-293 NOISE FILTER BOARD is available at several suppliers. Per ratio's suggestion, I did call Mitsubishi. Turns out there is no place to install that filter board in my unit. An engineer told me my unit already meets electrical noise specs and my Mitsubishi doesn't need it anyway.

He did ask if my dealer/contractor installed shielded cabling. That was news to me, and I don't know. They sure didn't ask me if I wanted shielded cable. I did ask them a few radio antenna questions during the installation and could tell they didn't know much about radio theory.

So, now I need to talk to the dealer again and see what they have to say about shielded cabling. I assume that's the control cabling that runs between the outdoor units and the inside wall units. Everything I find online seems to say shielded cabling is a requirement.

As far as adding ferrite chokes myself, I know from past RF noise experience that ferrite chokes won't help much unless they are placed very close to the source of the noise with the hot wires looped thru a choke several times. I can see the hot wires at the board are not long enough to do that, and I'm leery of replacing them with longer wires due to voiding the warranty.

allenm

My dealer/contractor did use unshielded control cable, but that's what Mitsubishi specifies for my mini-split units. The part number on the cable, which I checked myself, is the same one specified in their catalog for this model. At this point I'm convinced my mini splits are operating correctly and meet EMI emission specs.

So I've been making different changes to my radio antenna grounding system and have reduced the electrical noise the outside antennas pick up from the mini splits to an acceptable level. I would go so far as to say it's acceptable.

As far as trying to use a radio inside the house without an outside antenna, that's a lost cause. Time to accept it and move on.