Normally closed solid state switch

Discussion in 'The Projects Forum' started by czoz, Aug 18, 2012.

  1. czoz

    Thread Starter New Member

    Aug 18, 2012
    Here in Australia we have a premium domestic light switch (240v AC 50 Hz) called Clipsal Saturn. It has a 240v AC low power blue indicator light that can be wired one of 4 ways: always on, always off, on when the house light (load) is on, on when the load is off. The most popular configuration is the last one because it indicates whether the load is on or off and gives a nice blue light at the switch to find the switch in the dark when the house light is off.

    A problem arises when a two way switch is needed. I won't draw the circuit but surfice to say that the last option is not possible without an extra circuit of some sort. The manufacturer do not provide for this problem. My extensive research shows that the only way to fix this is to run a wire from the load to the switch and connect a NC relay. The load of the relay is the low power indicator lamp. When the house light is switched on, the relay switches off the indicator lamp.

    I would like to use a solid state solution instead of a coil relay. I see there are a few NC SSRs on the market but they have minimum load requirements and I'm not sure the indicator light would meet that. Also, those SSRs are overkill as they switch much larger currents than required.

    Ideally, I would love to get a cheap NC SSR or circuit that doesn't consume much power and will switch the small load and be controlled by 240v AC. Is this possible? I need about 10 but there is a bigger market here currently not provided for.
  2. ifixit

    AAC Fanatic!

    Nov 20, 2008
    Hi czoz,

    Can you not just wire the indicator light as shown in the attached drawing for the 2-way sw configuration?

    For safety reasons, keep the LED current low (less than 2.5 mA). There are amazing LEDs that shine quite bright even at only 1 mA. Diode D1 protects the LED when the 50Hz cycle reverses. R1 should be a half watt rating.