Hi i need to add a 24v AC led indicator on a circuit that already exists.The circuit has 24vAC permanent but for me to see i need to put a multimeter so thats why i want to put a Led circuit on.Any circuit ideas?
Put a 1N4148 (1N914) diode in series with a 1200Ω 1/2W resistor in series with the LED. The cathode of the LED must point the same direction as the Cathode of the diode. This will limit the current to about 20mA during the half cycles when the LED/diode is forward biased.
The reverse breakdown of most LEDs is only 5V, so the diode will prevent the reverse voltage from getting to the LED.
Cheap and dirty: use a 24 volt lamp instead. The things I am thinking of were made for the 10 button ITT key telephone busy lamp fields. I wish I could remember the part number but, they were about a size T2 with short push in pins for use on a circuit board.
They also make 24 volt LED lights. Just remember that these are DC so you will have to include a protection diode in series.