
Why do we use capacitors in parallel with DC motors? - peter_d_sherman
https://electronics.stackexchange.com/questions/490934/why-do-we-use-capacitors-in-parallel-with-dc-motors
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peter_d_sherman
Excerpts:

"Generally a 0.01~0.1uF capacitor is wired across brushed DC motors to reduce
radio frequency EMI caused by arcing between the brushes and commutator.
Sometimes two capacitors are wired in series, with the center connection going
to the case to 'ground' it at RF frequencies.

For best effect the capacitor(s) should be placed on or inside the motor. In
this case a capacitor has been included on the driver board. This makes it
less effective at higher frequencies because the wires from the board to the
motor will still be able to radiate EMI. Still it's better than nothing, and
may prevent misoperation due to interference from an unsuppressed motor
getting into the driver and input wiring."

And:

"The capacitor shunts (or "absorbs") the high frequency spikes from the
commutation and prevents damage to the driver chips.

A further factor not clear from the schematic is that snubber diodes should be
used to prevent inductive kick-back from the motor's inductance causing damage
to the driver's output transistors. While the diodes protect the driver, the
capacitors take the "edges" off the current spikes and help reduce EMI, etc."

