triac and optocoupler for low water pump switch

Thread Starter


Joined Sep 16, 2011
Hi I need help on this schematic, the aim is to control a water pump (max 35W of load) which has to be shut off when the water level goes low.
I searched for some floating switches but they are DC and low voltage (being in contact with water that makes sense).
I've come up with the schematic I attach, I have a triac which is piloted by a gate which controls the 230Vac terminals A1 and A2, on the other side I have a low voltage DC line (9v most likely) separated by a photo-coupler so that 230Vac don't get in contact with water.
I need help on the choice of the R1 resistance so as not to burn the gate of the triac and the suggested models for the photo-coupler and triac.
If you could tell me how to come up with the right resistance values I would be grateful.

Thank you



Joined Apr 5, 2008

You could take a look at the MOC302X as an optocoupler.
Those are specialy designed to drive triacs.

If you want to power the led in the optocoupler with a 9 Volts powersource, make Rin 390 Ohms and use the switch instread of the gate in the schematic.

I also have a link to the complete PDF on the MOC's:

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