I think the snubber is more effective across the contacts for arc suppression.
There is no rule that you can't have both.
C.C Bates developed a formula for calculating the resistance and capacitance value that is required for the RC network:
C = I^2 /10,
and
Rc= Vo /[10I{1+(50/Vo)}]V=I*Rc= (Rc/RL) Vo
- RC = Resistance of RC Snubber
- C = Capacitance of RC Snubber
- RL = Load Resistance
V=I*Rc= (Rc/RL) Vo
P = 60W
V = 240Vrms
Vpeak = SQRT(20*VRMS= 1.414213562373 * 240V = 339.41Vpk
P = I * V => I = P/V
= 60W/240V
= 0.250A
C = I^2 /10
** = (0.250A)^2/10**
** =** 0.00625 F (6246uF)
= 6246****uF
Rc= Vo /[10I{1+(50/Vo)}]
** =** 240V/[10/(1+(50/240V))]
** =** 240V/[10/(1+0.2083)]
** =** 240V/[10/1.2083]
** =** 240V/8.2758
Rc = 29 ohms
V= I*R => R = V/I
RL = VL/IL
RL = 240V/0.250A
RL = 960 ohms
The voltage induced at the contact opening can be determined by:
V=I*Rc= (Rc/RL) Vo
V=I*Rc= (Rc/RL) Vo
V = 0.250A*29 = (29/960)*240 = 7.25V
Note: freq of line voltage is not given (50Hz or 60Hz) ?
** If given, it is possible to calculate the Capacitive Reactance of the Snubber cap.**
Calculating Snubber Values
FYI, schematic convention is that the GNDs are shown at the bottom, not the top, so basically,
your circuit is upside down, regardless of being electrically correct. (power rails are shown at the top, GNDs
at the bottom of the schematic. The relay should be rotated 90 CW, which would be the GND at the bottom.
The 12V should be brought out to the left and then 90 CW bend so it is pointing up. The schematic is also
inconsistent because the water pump has no connection dots whereas everything else does. Either use them nowhere or everywhere. Also , it is not necessary to draw the water pump as box. It is an electric motor and should be drawn as a motor, not a box. Why use symbols for capacitors, resistors and diodes
but not inductors ? Either an inductor symbol or a motor symbol (circle with M insde) is correct.
