triac and optocoupler for low water pump switch

Discussion in 'The Projects Forum' started by dedioni, Sep 16, 2011.

  1. dedioni

    Thread Starter New Member

    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
  2. bertus


    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:

    Last edited: Sep 16, 2011
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    Use the dc float switch to trigger a relay coil.. Relay contacts switch the AC