Pulse Width Modulation (PWM) charging may cause interference in sensitive loads in the system during charging. The SunSaver switches current at 300 Hz. PWM switching noise can sometimes be heard in the controller itself, the wiring or wiring connections, or the system loads. AM radios and CB radios are especially prone to PWM interference. Noise in the controller or wiring is caused by mechanical resonance when current is switched through the circuits. There is little that can be done to remedy this issue. However, noise/interference in the system loads can usually be reduced or eliminated by the following:
Minimize cable runs between components
Twist power pairs(+/-) to reduce radiated noise
Good system grounding
Add capacitance across load power(at load input, 22000uf or more)
Add a line filter. some have had success with car audio filters that eliminate alternator whine. If these measures do not eliminate or reduce interference to acceptable levels, the controller can be modified to reduce the switching frequency. The 3rd generation SunSaver has a wire loop under the faceplate. If this loop is cut, the controller will reduce the switching frequency to ~1 Hz. Refer to the SunSaver Operator’s Manual for more information.
Some Morningstar controllers allow for operation in a ‘low-noise’ state. Check your controller documentation for details.