I’ve been thinking of some non-standard ways to reduce EMI noise at the contacts of relay(s) switching various AC loads. For example, when controlling a 4 Relay Module with an Arduino, the user’s code could:
Prevent multiple relays from energizing simultaneously by assigning, for example, time delays of 0, 50, 100 and 150 ms before energizing relays 1, 2, 3 and 4 respectively. I would think that avoiding simultaneous EMI noise emission from multiple contacts and coils would have beneficial effects.
Detect zero crossings and energize the relay so that the contact bounce period is precisely centered on the zero crossing that occurs 16.67ms later (60Hz AC) or 20ms later for 50Hz AC. If the contact bounce can be kept within 30 degrees of the zero crossing, then the peak voltage seen by the contacts during switching would be <= 1/2 the applied voltage.
My question is, for the same switched load, if the switched AC voltage is reduced by 1/2, how much would this mathematically reduce EMI levels?