>
>
> >
>      Is there a way of dimensioning the zener diode minimum power needed?
>

That question is too imprecise to be sure what is being asked, but ...

Zeners will conduct the current in the relay coil when power is turned off.
Call this say Ir.
Zener initial power dissipation will be Vz x Ir.
Energy to be dissipated is 1/2 x Lr x Ir^2
where Lr is the relay coil's inductance.
As well as zener dissipation you will dissipate Ir^2 x Rw where Rw is
resistance of all items in the circuit including the relay coil and wiring
resistance.

Rather than determining zener "power" per se it is probably easier to
determine if the zener can safely dissipate the total inductor energy -
actual dissipation will be somewhat less due to resistive losses.


         Russell
--=20
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