Very simple. As the incandescent lamps are claimed to be environmentally dangerous therefore everywhere condemned by criminal imprisonment laws, utilized mandatory, completely forbidden (except the halogen) about ten years ago and substituted by spiral-plasma compact lamps (mainly), the last are ALWAYS giving a rather hard high frequency emission at E plane (about meter afar), at H plane (about a foot afar) and via wires (about tens of meters afar).

For example, when this change of technologies hit our underground lab spaces, where we extensively use the "corridor switcher" circuit (on from one end and off from other end as well the reciprocally when going backward or another is going same corridor toward): there after we exchanged the 15 lamps for 75W each toward 15 lamps 8W each just ALL switchers was burned out with a smoke and fire at set on or set off transit. After changing the switchers they burnt immediately, and next time after all circuits was inspected and lamps was exchanged again and again. Until we find that high freq component is high enough that 8W lamp gives a 8 mm long plasma tail in switcher. Logically, all switchers have 1 mm gap, thus the switch-on/off moment produces a straight plasma channel between phase wire and gnd wire. Only solution was to find a very damn expensive switchers with very wide contact-gap thus the last years this problem is completely cured.

Therefore I know for sure, You just may measure the HF component on some small capacitor and if there is no oscillation, know the lamp is dead. And vice versa, if there are oscillations it means the lamp is shining.

 

For a safe, no electrical connection needed...
Get a clip on current transformer... (go for lowest current version)
https://www.ebay.com.au/itm/15-20-3...hash=item4681104976:m:mR9Jx8YONU0aOOZkEk3CQow

And have ONLY ONE of (was "on". Thanks for spotting that @AlbertHall ) the power wires feeding through it.
For more signal, if you need it, loop the single power wire around a few times.
Add a bridge rectifier and capacitor to the output and a small relay. The lamp current will keep the relay operated and when it blows, the relay releases and turns on an alarm.

 

And have ONLY ONE on the power wires feeding through it.

And have only one OF the power wires feeding through it.

 

And have only one OF the power wires feeding through it.

OOPS Another typing error I missed

 

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!

Here's one using a standard transformer, a relay and a buzzer.



Regards,

Nandu.

 

Here's one using a standard transformer, a relay and a buzzer.

Interesting circuit.
Apparently depends upon the transformer saturating when its secondary in series with the bulb exceeds 6V or so due to the bulb current.
Of course that could overvoltage the relay on the primary (output) side.

 

Thanks, crutschow!

I'm assuming that full load current through the secondary winding would ensure 6V across it and a burden of optimal value across the primary winding (to be determined by trial) would do likewise for 230 V. The relay coil specs have been left open for that reason.

Regards,

Nandu.

 

I'm assuming that full load current through the secondary winding would ensure 6V across it and a burden of optimal value across the primary winding (determined by trial) would likewise for 230 V. The relay coil specs have been left open for that reason.

Okay, that makes sense.
The burden resistor would need to dissipate about 4.5W or so.

 

The burden resistor would need to dissipate about 4.5W or so.

I make it less than that.
175W lamp @ 230V = 0.76A tranny input.
Turns ratio of tranny = 230/6, so tranny output current = 0.76A*6/230 = ~ 20mA.
A 24V relay such as this has a 20mA rated coil and would act as the burden resistor, dissipating 480mW.

 

A 24V relay such as this has a 20mA rated coil and would act as the burden resistor, dissipating 480mW.

Yes, good catch.
I obviously wasn't thinking about using a lower voltage rated coil that would draw more current at less than 230V.
That then also gives a voltage drop on the primary side of less than a volt.

But that's a DC coil relay.
Wouldn't you want an AC coil to avoid having to rectify the voltage?

 

Wouldn't you want an AC coil to avoid having to rectify the voltage?

Yes. Touche! Good catch .

 

Okay, that makes sense.
The burden resistor would need to dissipate about 4.5W or so.

Hi crutschow,

4.5 would be the VA!

Regards,

Nandu.

 

I make it less than that.
175W lamp @ 230V = 0.76A tranny input.
Turns ratio of tranny = 230/6, so tranny output current = 0.76A*6/230 = ~ 20mA.
A 24V relay such as this has a 20mA rated coil and would act as the burden resistor, dissipating 480mW.

Hi Alec_t,

I had also arrived at the 20 mA burden and considered a 'sensitive adjusted' relay with nominal coil current close to 20 mA. A 230 V 30 kΩ 'power adjusted' relay also appeared to be suitable.

https://oenindia.com/uploads1/products/67_20160531012503.pdf

But my doubts on the actual functioning of a normal transformer as a CT got the upper hand and I decided that determining the optimal value by trial would be the way to go.

Many thanks.

Regards,

Nandu.

 

On second thoughts, the transformer could be done away with should a 'sensitive adjusted' relay with nominal coil current close to 0.75 A be available!

Regards,

Nandu.

 

I see that I came late to the party. I would consider placing a thermisteor in a place that is heated by the lamp. It is automatically optically isolated, and it senses the critical parameter -whether or not the dog house is being heated.

 

Yebbut, that solution was specifically ruled out in post #1.

 

This might do the job. It has a current transformer built in.
https://www.ebay.co.uk/itm/5V-0-5A-...834521?hash=item2adcf78199:g:mTAAAOSwjyZeAHMg

 

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!

Circuit below will monitor lamp current.
Note:
Transformer Tr1 is used because of this forum rules. Noted: Moderation,E

 

In the post #38 circuit, when the lamp is working there is about 130mV rms across the piezo. Is that likely to produce an annoying background sound?

 

If you could accept an optical warning instead of an audible one, then just a standard 6V 6W bulb in series with the heat lamp might suffice. The bulb would be under-run at only 0.75A so should have a long life.