So, lets say you have a mechanical switch connecting an AC (mains) source to a small inductive load (say, a single speed ceiling fan) via a long wire (1000' of NM). When the switch is turned off, how much of the energy from the motor's back-EMF gets radiated, and what would a spectrum analyzer plot of this radiation look like were you to do this in an EMC test site?
Electronic – Does inductive back-EMF create significant radiated emissions on long load wires
back-emfemcinductive
Related Solutions
LEDs are a nonlinear load and probably these lamps will not have a power factor correction converter. This means that the current will not be sinusoidal therefore you will have some reactive power flowing. There may be a PFC choke before the rectifier bridge.
If you want to measure the power factor and harmonic content just take a scope with voltage and current probes and measure line voltage and line current.
PS. This it how you distinguish China Export mark from European CE:
If there is no diode clamp on the motor to catch back emfs when the motor current is interrupted, that energy in the motor will force current to flow through the parasitic diode of the MOSFET to the VPWR rail. Adding a "soak up" capacitor on the rail ensures that the VPWR rail won't rise very much. However if you have an output clamp this will largely prevent this from happening and a much smaller capacitor can be used on VPWR.
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Best Answer
I'm going to answer this here, even though I've got you covered in the comments. The snubbing circuit should go at the load.
A great way of thinking about WHY, is that the source of the back EMF is the inductor on the fan. The farther away the snubber is from the source, the more wire there is to act like an antenna to radiate the back EMF as EMI.