The RFI kit is designed to suppress RFI caused by Solar micro-inverters, power optimizer, and solar arrays by electrically isolating the “antenna” wires used to connect the various devices.The cabling between the PV array, the micro-inverters or power optimizers and their connection to the electrical bus combining their individual outputs can be considered “antennas” for the pulse switching circuits of the individual devices thereby causing radiation at very low fundamental frequencies with harmonics that can cause undesirable radio interference in the 1-30 MHz (and sometimes higher) frequency range.This interference may be objectionable to the owner of the solar installation as well as neighbors who may also experience the interference to their electronic devices.
THE RFI KIT FILTERS ONLY SUPPRESS COMMON MODE CURRENT (SIGNALS) THAT ARE COMMON TO ALL WIRES IN THE CABLE, AND DOES NOT EFFECT INDIVIDUAL DIFFERENTIAL SIGNALS ON EACH WIRE. THE FILTERS HAVE NO EFFECT ON THE NORMAL SIGNALS CARRIED WITHIN THE CABLE.
Micro-inverter RFI
Ferrite cores (snap on) are snapped over the two (+/-) cables from the solar array module and the two wires hooked to the “string” connecting the micro-inverters together. Suppressing RFI on all wires in and out of the micro-inverters helps to reduce any broadband RFI “noise” generated in the SOURCE switching circuits (typically at 50-200KHz and harmonics thereof). Two ferrite cores are required for each micro-inverter/PV array – one ring for the PV DC cables and a snap on for the micro-inverter cable to the string bus – size to fit the trunk cable with 1 or 2 turns.
Application Note for Enphase M190/M215/M240/M250 series Micro-inverters (and similar other brands). For each PV array/micro-inverter use a RFI-PV-MI filter kit with a ring (ID=1.4″/36MM) ferrite for installation on PV module DC cables to micro-inverter and a snap on (ID=.4″/10mm) filter for the data/trunk cable output of the micro-inverter. At the connection of each junction box and the Engage cable install a RFI-PV-JB filter (ID=1″/26MM) with multiple turns through the center.
50 ohm coax to 75 ohm balanced output baluns are useful for low (< 1 wavelength) dipoles exhibiting 75 ohm characteristic impedance or for matching to balanced ladder line whose endpoint impedance is near 75 ohms.
50 ohm coax to 75 ohm CATV coax connections are easily done with a 1.5:1 unun with SO-239 connectors on input and output. Likewise 50 ohm coax to unbalanced verticals or loads near 75 ohms can be matched with a 1.5:1 unun.