Help with detecting open switch

[tony10]

I have a 24VAC circuit which has 3 switches in series with a relay. If one of the switches open then the relay turns off. I would like to know the best way of turning on one of 3 LED's to determine witch switch is opened.

 

[davenn]

hi Tony

put a LED and appropriate resistor in parallel with each switch
for any one switch, when the switch is closed, it will put a short cct across the LED and resistor ad the LED wont light
when the switch opens, the LED and resistor will now form part of the circuit and the LED will light

Dave

 

[duke37]

You will need a diode in inverse parallel with the led to shunt the 34 peak reverse volts. Also, the load must need enough current to NOT operate on the led current.

 

[Gryd3]

You will need a diode in inverse parallel with the led to shunt the 34 peak reverse volts. Also, the load must need enough current to NOT operate on the led current.

The fun part here will be that sometimes a relay will still 'hold' with a much smaller voltage than required to activate it. There was a guy not long ago that had issues with that using light up door bell buttons.
If the relay won't unlatch with a LED connected as mentioned above then you will need to be creative. (Perhaps by running the LEDs in parallel with the power supply... Sounds odd I know, but if you connect a LED at or after each switch, then you will be provided with a visual indication of the *first switch that opened by seeing which LED(s) turned off.)

 

[duke37]

I had a look at a three pole 230V AC changeover relay some time ago and it would pull in and drop out at the same AC voltage but when driven with DC, it would hold right down to 8V.

 

[Colin Mitchell]

LEDs work on 1mA. Use a super bright LED