Circuit to remotely show incandescent mains bulb failure?

Thread Starter

Chris Wilson

Joined Dec 2, 2011
14
Hi, I am pondering the simplest way to have an audible warning in the house if a dog kennel infra red incandescent 175W bulb filament fails. I am sure once I achieve a normally closed or open device I will be able to find a short range transmitter and receiver to do the RF side. But how to perhaps monitor 50Hz AC mains current with a circuit to change state on no load being presented? The device needs to be at the supply end of the cable and not in the kennel, which rules out heat sensors or optical sensors near the lamp.. Thanks for any ideas!
 

AlbertHall

Joined Jun 4, 2014
10,243
You could wind a few turns of wire round a reed switch. The reed switch will be closed by the magnetic field from the coil. This needs no direct connection to the mains supply so it is inherently safe. You could also use a current transformer, again no direct mains connection, but extra circuitry would be needed to close a contact from the transformer signal.
 

Thread Starter

Chris Wilson

Joined Dec 2, 2011
14
Hi Albert, thank you, that sounds simple and safe, I am not doubting you when I ask if AC mains will hold a reed switch closed, and it not require DC? Would AC not try and make it chatter at 50Hz or do they have sufficient hysteresis? I guess I could add rectification though, if required... Thanks again!
 

Yaakov

Joined Jan 27, 2019
1,612
Hi, I am pondering the simplest way to have an audible warning in the house if a dog kennel infra red incandescent 175W bulb filament fails.
You could make your own optoisolator with a neon lamp and a photoresistor.

It the lamp is in series with the bulb, it will not light unless the bulb is missing or open.
 

AlbertHall

Joined Jun 4, 2014
10,243
It the lamp is in series with the bulb, it will not light unless the bulb is missing or open.
:eek: If you put a neon in series with the lamp one of two things will happen:
1. If the neon includes a resistor for the supply voltage only the neon will ever light.
2. If there is no resistor the neon will emit magic smoke and cease to exist.
 

Yaakov

Joined Jan 27, 2019
1,612
:eek: If you put a neon in series with the lamp one of two things will happen:
1. If the neon includes a resistor for the supply voltage only the neon will ever light.
2. If there is no resistor the neon will emit magic smoke and cease to exist.
The lamp will be ~95Ω the NE2 has a dropping resistor of 100KΩ.

This is the method I've used many times for a blown fuse indicator. I know that works, what am I missing about the incandescent?
 

AlbertHall

Joined Jun 4, 2014
10,243
The lamp will be ~95Ω the NE2 has a dropping resistor of 100KΩ.

This is the method I've used many times for a blown fuse indicator. I know that works, what am I missing about the incandescent?
Across a fuse the neon works a treat. While the fuse is intact the neon is shorted. When the fuse blows the supply voltage appears across the neon and resistor and the neon lights. All is good.

With the incandescent lamp, if you connect the neon with resistor across the lamp then the neon will be lit when power is on regardless of whether the lamp is blown or not.
If you connect it, with resistor, in series with the lamp the 100k resistor would be in series with the lamp and would prevent the lamp from lighting. In series without resistor the full lamp current would pass through the neon and destroy it.
 

Yaakov

Joined Jan 27, 2019
1,612
Across a fuse the neon works a treat. While the fuse is intact the neon is shorted. When the fuse blows the supply voltage appears across the neon and resistor and the neon lights. All is good.

With the incandescent lamp, if you connect the neon with resistor across the lamp then the neon will be lit when power is on regardless of whether the lamp is blown or not.
If you connect it, with resistor, in series with the lamp the 100k resistor would be in series with the lamp and would prevent the lamp from lighting. In series without resistor the full lamp current would pass through the neon and destroy it.
I would expect the intensity of the NE2 to be noticeably different in the absence of the incandescent filament.
 

AlbertHall

Joined Jun 4, 2014
10,243
I would expect the intensity of the NE2 to be noticeably different in the absence of the incandescent filament.
How are you connecting the neon and, I assume, its resistor?
In parallel with the lamp?
The lamp is connected to the supply by a switch so the neon will see the supply voltage. That voltage will be affected only minutely by the current drawn by the lamp. Remember the neon is the supply end of the cable feeding the lamp.
 

Yaakov

Joined Jan 27, 2019
1,612
How are you connecting the neon and, I assume, its resistor?
In parallel with the lamp?
The lamp is connected to the supply by a switch so the neon will see the supply voltage. That voltage will be affected only minutely by the current drawn by the lamp. Remember the neon is the supply end of the cable feeding the lamp.
In parallel, at the lamp is how I imagined it. If it must be sensed at the far end, without any additional link—wired or wireless—it may not work. I might have missed something about the specification, if so, I withdraw the suggestion.

Thanks for pointing that out.
 

AlbertHall

Joined Jun 4, 2014
10,243
In parallel, at the lamp is how I imagined it. If it must be sensed at the far end, without any additional link—wired or wireless—it may not work. I might have missed something about the specification, if so, I withdraw the suggestion.

Thanks for pointing that out.
If it was at the lamp end you wouldn't need a neon to tell you if the lamp was working.
 

Thread Starter

Chris Wilson

Joined Dec 2, 2011
14
What about a low value high current shunt in series with the lamp at the power socket end that has its voltage drop feeding a TRIAC? Turn on current of a big incandescent bulb might make the shunt value difficult to balance, turn on current blowing up the TRIAC versus holding it on when the lamp is lit perhaps? All good stuff, thanks all :)
 

AlbertHall

Joined Jun 4, 2014
10,243
What about a low value high current shunt in series with the lamp at the power socket end that has its voltage drop feeding a TRIAC? Turn on current of a big incandescent bulb might make the shunt value difficult to balance, turn on current blowing up the TRIAC versus holding it on when the lamp is lit perhaps? All good stuff, thanks all :)
That could work with a resistor in series withe triac gate to swamp variations in the shunt resistor voltage and triac gate requirements.
 

Rich2

Joined Mar 3, 2014
172
Keep it simple.
Supply the kennel lights with a plug in LCD watt meter, when the wattage reduces from it's normal level, a bulb filament has failed :cool:
 
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