Charge Controller Filter

This is an up to '3 port' filter which is particularly usefel for reducing RFI from MPPT Solar Charge Controllers (SCC) used as part of an off-grid or ham shack 12VDC power system.  It uses simple CLC filtering of pairs of input and output lines  with the addition of "Guanella style"  transformation to isolate unwanted noise currents that may be generated by higher power switching power circuits used for obtaining and maintaining charge of local storage batteries.   This circuit accomplishes isolation for both differential RF noise - noise across each pair of lines associated with an input power source such as a photo-voltaic solar panel, PV, a Battery, BAT and a load, LD,  and also for common mode RF noise that might be coupled from the SCC to the 'outside' world.

Because SDR receivers and sites can be very sensitive with as little as 50 picoamperes of unwanted noise current causing harmful interference to communications, a very large degree of isolation between multi-100watt SCCs and receiver inputs. Paths for these kind of unwanted current may be varied but this design seeks to place the entire SCC on an "RF island" so that no currents can escape to cause QRN.

In addition to the conventional shunt-choke-shunt LPF filtering nature for each conductor, there is also the same present for each differential pair.    The use of a common toroidal core adds yet another degree of isolation by greatly increasing the impedance between the 'inside' where the DUT is located and the "outside" world.

The result of using this circuit can be ten's of dB of reduction in stray currents and the degradation they might cause to a sensitive receiving system's noise floor.

4 turns of AWG#12  red/black pair power conductor can be wound around the common 2.4" core BEING CARFUL TO WIND EACH IN THE SAME DIRECTION to provide the extra isolation of common flux paths and resulting in high RF impedance between the inside/outside regions.

In general it may be found that in addition to keeping the MPPT  'floating' with this circuit it will also be useful to keep it separated from sensitive receiving systems where magnetic coupling with the SCC might provide an alternate unwanted ingress path.

 If raw PCBs are hand assembled, the capacitors should all be assembled before the toroid is prepared and attached.  Assembly is easier if each of the 2wires x 3pairs x 2zone = 12 conductors is pre-stripped and then the 6 pairs pushed through the PCB before finally bending the exposed wire away from the via centers and soldering with adequate heat to easily reflow solder.