Cursitor Doom wrote:
On Wed, 30 Dec 2020 21:58:34 GMT, Harry Bloomfield, Esq.
wrote:

Chris Green laid this down on his screen :
Not to mention that switching DC is harder on contacts than switching
AC.
A suitable diode across the contacts will help.

ITYM to reduce back EMF one would use a diode reverse-biased across
the coil of the relay. To stop sparking across contacts a suitable
capacitor would be a better bet.


These are referred to as "snubber circuits" and
can be tuned for good results. The people in
sci.electronics know how to do that. There was
at least one guy over there, who wrote a textbook
of electronic design. A kind of "resident perfessor".

http://electronicsbeliever.com/snubb...sign-analysis/

An RLC makes sense, since the R is the dissipative part. That's
where the electrons go to die.

And you "tune" the snubber to the thing to be snubbed. It's
not a random thing. Someone who knows what they're doing
can reduce the ringback to almost nothing. If the characteristics
of the load are not known with any precision, you can breadboard
the circuit and change values until it's tame. Snubbing a relay
coil should be a slam-dunk, as the relay composition will not
vary too much from unit to unit.

Paul