(1) Regarding the charger type: If it was sold for an RV, that charger most
likely is a multi-mode charger that switches to a float charge "maintenance
mode" after the main recharging is done. Though the term "trickle charge"
is often used as a synonym for float mode, there's a key difference. Float
means constant voltage at any current up to a limit value, while trickle
means (more or less) constant current regardless of battery voltage. Only
NiCd batteries tolerate continuous trickle charging well. RV batteries will
be deep-cycle lead acid, either wet cell or valve-regulated (so-called
"sealed" lead acid). The folks who make RV battery chargers design
accordingly. Trickle chargers are not as popular as they once were for
consumer products, because extended trickle charging ruins NiMH cells.
(2) The noise profile means it's most likely a switch-mode design. If the
neighbor is cooperative, ask to see it. Look for FCC or "CE" compliance
markings, and get the make and model if possible. The idea is to find out
if there's any indication that the manufacturer claims to meet FCC
regulations, and to clearly identify the offending item if you do end up
filing a complaint with the FCC. As an "unintentional radiator", this
charger should be marked as required by FCC rules 15.19 (3):
"All other devices shall bear the following statement in a
conspicuous location on the device:
This device complies with part 15 of the FCC Rules. Operation is
subject to the following two conditions: (1) This device may not cause
harmful interference, and (2) this device must accept any interference
received, including interference that may cause undesired operation."
(3) Changing the socket probably changed the interference by re-arranging
the wiring geometry, making it a more effective antenna. The presence or
absence of a ground wire can alter the resonant frequencies of the AC
wiring, but won't magically stop common mode currents. Radiation still
occurs from from the power cord, the house wiring back to the ground bus
bar in the breaker panel, and the ground wire from the breaker panel to the
building ground (which almost certainly is not an effective ground for RF).
(4) Properly applied ferrites on the charger's input *and output* leads may
help. My experience is that outputs of chargers and power supplies often
are quite noisy, probably because the standard emissions tests measure
conducted noise only on the AC supply leads. Couple common-mode output
noise to long conductors (such as the 12VDC system in an RV) and you have
more interference than the RFI test lab measured.
(5) I don't recommend opening up the charger or making any modifications to
it. Line voltage switch mode supplies are both dangerous and expensive. If
anything goes wrong afterward, your neighbor will likely blame you. Don't
take the risk: if external ferrites aren't enough to clean it up, it's a
job best left to the company that built it (besides, it's their product so
it's *their problem* to fix it).
Good luck!
--Tim (KR0U)
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