LED on mains voltage?

[Andy5112405]

Originally Posted by AndrewT

I want to monitor the presence of voltage on each of the three phases in my house (230/415Vac). We suffer very frequent power cuts.
I can put in a diode followed by a resistor then a LED.
The resistor dissipates quite a lot of power. or
I could use a constant current source but it would need to be Hi Voltage. or
I could wire in three transformers & then LED at low volts.
I don't like any of my solutions.
Can anyone suggest a cheap, safe & simple circuit?
regards Andrew T.

Depends on what you class as SAFE.

The simplest solution is an X rated cap with a diode, a resistor and an LED.

This is inherently DANGEROUS unless you take precautions about ensuring everything is insulated.

The safest solution is with a small transformer, a diode and a resistor,

This is inherently SAFE but is ungainly and inelegant.

[Mooly]

Originally Posted by shushz

Hi,

I'm very new to the field of electronics and trying to learn from online resources so forgive me if the questions are stupid, but could someone please explain what is the purpose of R2 in the above diagram proposed by Elvee and why does it have to be WW?
Also, to my understanding using capacitor to drop voltage with such low resistance would result in rather poor power factor of the circuit. Am I right? Is it something to be concerned about, or it can be disregarded for such low currents?
If not, how can the power factor be corrected?

The power factor is really a non issue with so small a cap (the 0.1uf).

R2 is often used on this type of circuit although here it is not really needed. Usually its a small carbon type...

If the 500uf cap were ommited and just an LED used then its possible at switch on that (depending on where in the cycle the mains was) that the peak current of the LED could be exceeded. The 500uf cap absolutely swamps that issue though.

R3 across the 0.1uf cap must be a high voltage resistor. Resistors do have max voltage ratings, even if the wattage is well withing spec. Sometimes good practice to use two series connected ones. Its purely to discharge the 0.1uf on switch off to prevent a small shock if you touched it later.

[shushz]

Great :-) I hoped so, but feared I just didn't understand something.

Mooly and Andy thanks a lot for your answers.