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.
AM broadcast transmits on a low frequency with large antennas. Consequently it takes a large antenna to receive the signals. Typical “antennas” are AC house wiring, phone lines, long satellite or cable TV cables, DSL/CAT5 lines running between rooms, etc. The device wires that connect to these “antennas” need to be choked with as many turns through the ferrite as possible. Some installation examples are shown below on this page.
For AC/ DC power cords and coax cables the F240-77 (2.4″ OD, 1.4″ ID) “Donut” toroid is the most popular. Also available are smaller toroid donuts and Mix 77 beads. Shown below is a graph with 8, 10, and 12 turns through the toroid – obviously more turns has higher choking impedance. Mix 77 toroid products are HERE and Mix 77 small beads (for small wires) are HERE
F240-77 Turns Comparison from .1 – 8.1 Mhz
Shown below is a graph of frequency response verses choking magnitude for a F240-77 in the AM Broadcast band for a 12 turn coil around the toroid. (Same info as above but different frequency range).
F240-77 Choking Impedance in AM Broadcast Band
Typical Installations for Donut/Ring Toroids
 AC Cable on F-240 Toroid – 6 turns |
 Ethernet Cable on F-240 Toroid – 7 turns |
 Audio or Mic cable on F240- 12 turns |
Extra Mix 75 Snap On Beads HERE – VERY effective for AM Broadcast RFI