AC300 interference issues (RFI)
In case anyone is interested, I report my experience with interference generated by Bluetti's AC300 inverter and MPPT controller.
If you are not an amateur radio operator, I think this issue can be considered just a curiosity, but it can be useful to know in case one day some of your neighbours come knocking on your door, having identified the source of the disturbances...
Of course, I was aware of the problem of noise generated by inverters in particular, but I naively thought that, given the company's reputation and the high cost of these products, this problem was not present in this unit. The AC300 as far as its work with photovoltaics is concerned, however, works well, is easy to use and well protected.
The AC300's inverter generates considerable broadband noise, detected in particular from 10 MHZ to 50 MHZ (probably even beyond, but I have not checked), making it impossible to listen to weak signals despite the use of noise reducers available in receivers.
At first I tried ferrites and then AC filters, but without appreciable results, the disturbance generated by the inverter persisted, and was proportional to the AC load connected, the greater the load = the greater the disturbance.
Even when disconnecting the cables and switching on the inverter with only the battery connected, the disturbance was present (the fact that the AC300 housing is plastic, of course, does not help).
At this point the only solution was the Faraday Cage... I made a wooden frame (with the front movable by means of two hinges, to insert the AC300 and the battery), which I covered with aluminium netting used for mosquito nets (112x1000 cm. taken from Amazon); I put two layers on top of each other except for the two side panels, to facilitate air circulation.
The cage must be hermetic and complete, even a small opening lets out disturbances; at this point it remains to filter the AC output and I installed some filters normally found on Amazon followed by some ferrites I had in the drawer (of unknown material) and other more effective ferrites, the Würth 74271151 the white ones in the photos (I made two, one inside the cage and the other outside, probably only one is enough...). And so the inverter problem appears to be solved (I also installed a filter on the AC input).
At this point, there remains the problem of interference generated by the MPPT controller, which consisted of harmonics heard every 20 KHZ, and again, the higher the input power from the panels = the greater the intensity of the interference.
I installed numerous ferrites on the four input cables connected to the photovoltaic panels, but this seemed to have no effect, so I had to interpose a filter, and having seen on one of the links at the end, that the same kind of filters had been used for AC I tried it, and this solved the problem. (In my case the current from the input panels is currently only 5 A max, with high currents I think it is better to use filters of at least 30 A...).
The Faraday Cage network is of course NOT connected to the AC300 earth, and is currently isolated from earth; when I move everything to another location then I plan to install a dedicated earth connection for the Faraday Cage network. At present, metal AC (and DC) filter housings are connected to the Faraday cage (and not to the inverter ground).
It should be noted that the network does not block Wi-Fi and Bluetooth signals, so one can use the appropriate app Bluetti, to control the AC300; one can still interact with the touch screen panel by widening the mesh just a little and inserting a thin plastic or metal rod (in the picture one can see a white 'thing' that is a small calendar holder).
Good luck,
Ferruccio I1TXD
(It would be interesting to compile a list of (tested) inverters and charge controllers that do not generate interference.... : E-mail).
Some link :
English version translated with : Deepl