Hello all, we have an Axpert vm iv. I am getting very bad rf interferance on my stereo (only phono stage), I have tried so many solutions. But it seems by a matter of elimination be related to the PV cables. If they are disconnected from the inverter, no issues. You put one in, humming, 2 in, louder humming. They can be charging or not, they can even be disconnected at the panels, but still noise. disconnect from the actual inverter, it stops! ANY IDEAS?

High-frequency switching noise. Axpert VM IV inverters use a high-frequency DC-DC converter between PV and battery. Even when not actively charging, the input stage sits at a high impedance and the MPPT circuitry can still “sniff” the PV lines with high-frequency pulses. Those pulses are easily radiated from long PV cables. The PV leads run from the roof and act as a big antenna feeding noise into your house wiring or into the air. When you unplug them from the inverter, that antenna disconnects from the noise source.

Run the two conductors(pos and neg) very tightly together in metallic conduit (steel or aluminium). Bond the conduit to earth at one end (preferably the inverter side) and fit large ferrite cores on each PV lead right at the inverter’s PV terminals. Wrap as many turns as you can through each core. This dramatically reduces conducted RF going back up the cable.

Amazing, thank you so much for your detailed reply. I makes a lot of sense, I can hear the noise if i stand right next to the inverter also. The slight isssue I have though is that the cables actually come in under the house from the field where the PVs are, they run in plastic conduit so can be pulled out and put back in. So in theory i could wrap them tightly together and wrap them in aluminium tape to act as shielding and bonding, then add the ferrites at the inverter and and ground all. Do you feel this would help? Its strange because it never used to do it, I guess the other option might be to replace the MTTP or indeed the whole inverter in time? Many thanks again for your reply, if you have any other words of wisdom that would be great.

Phono preamps amplify microvolts from a cartridge up to hundreds of millivolts. Any RF picked up by cabling, tonearm ground, or even your mains earth will be heard as hum/buzz. Even with standard solar cable, tightly twist the PV+ and PV- conductors together from the point they leave the inverter until they enter conduit. This reduces loop area and cancels radiated fields. I use to install induction loops for boom gates and if you dont twist the 2 induction loop wires together where it exsist the conduit at the controller the boom gates opens and acts irratically. I used a cordless drill to wind the end tails together just take care not to damage the insulation.

49 minutes ago, ultranox said:

So in theory i could wrap them tightly together and wrap them in aluminium tape to act as shielding and bonding, then add the ferrites at the inverter and and ground all. Do you feel this would help?

Have never tried it but cant see why it cant work.