Circuit to give an RF remote audible indication of a mains bulb failure

[Chris Wilson]

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 nomally closed or open device I will be able to find a short range transmiiter 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!

 

[Nigel Goodwin]

A year or so ago I posted EXACTLY what you need - but I can't find it!.

It might be at work?, I'll have a look tomorrow.

Essentially it's just a low value resistor in series with the mains, the voltage drop across it is used to trigger a thyristor, which turns a relay ON, and the relay is used to turn an indicator light ON or OFF.

I got the (very simple) circuit from a commercially available unit that I was asked to try and repair - it was used in a school to monitor an extractor fan that was used to remove potential Radon gas build-up. In the event there was no fault with it - they expected the light to be ON all the time, where it was actually designed to only come ON if the fan failed. As it had an SPDT relay in the unit, I rewired it to the other contact to work in the way they expected.

 

[unclejed613]

you could (since all you need to sense is the current) is run either of the wires going to the bulb (doesn't matter if it's hot or neutral) through the center of a toroid, and have a lot of turns of wire wound on the toroid as a secondary winding for a current sensing transformer. while the bulb is lit, there will be an AC voltage across the secondary. the secondary voltage could be rectified and used to turn on a transistor. the transistor drives a relay, and you run the power to the transmitter through the NC contacts on the relay. if the bulb filament goes open, the voltage across the toroid disappears, the relay de-energizes and applies power to the transmitter.

 

[Chris Wilson]

A year or so ago I posted EXACTLY what you need - but I can't find it!.

It might be at work?, I'll have a look tomorrow.

Essentially it's just a low value resistor in series with the mains, the voltage drop across it is used to trigger a thyristor, which turns a relay ON, and the relay is used to turn an indicator light ON or OFF.

I got the (very simple) circuit from a commercially available unit that I was asked to try and repair - it was used in a school to monitor an extractor fan that was used to remove potential Radon gas build-up. In the event there was no fault with it - they expected the light to be ON all the time, where it was actually designed to only come ON if the fan failed. As it had an SPDT relay in the unit, I rewired it to the other contact to work in the way they expected.

Hi, thanks for that, I have found your circuit here: https://www.electro-tech-online.com/threads/question-regarding-amperage.154766/page-2#post-1335300

Only worry is a 175 W incandescent bulb will have a high turn on current from cold, so would this make choosing a suitable series resistor value to work, yet protect the TRIAC on turn on tricky? I like it's elegant simplicity though, thank you.

 

[Chris Wilson]

you could (since all you need to sense is the current) is run either of the wires going to the bulb (doesn't matter if it's hot or neutral) through the center of a toroid, and have a lot of turns of wire wound on the toroid as a secondary winding for a current sensing transformer. while the bulb is lit, there will be an AC voltage across the secondary. the secondary voltage could be rectified and used to turn on a transistor. the transistor drives a relay, and you run the power to the transmitter through the NC contacts on the relay. if the bulb filament goes open, the voltage across the toroid disappears, the relay de-energizes and applies power to the transmitter.

Thanks unclejed, this too sounds likea pretty simple way of doing it, any ideas on a suitabble core material? I am into amateur radio and the junk box may produce something. Are we looking at dust iron material toroids here?

 

[Reloadron]

Aside from Nigel's fine suggestion a 175 watt bulb will draw about 0.800 Amp. I assume 220 Volt since you mention 50 Hz. One popular method is wrap a few turns of the high or low side wire around a plain reed switch. It doesn't take many turns. When the lamp draws current the coil field will close the reed switch. If the lamp is open the reed switch will be open. Here in the US I can buy a magnetic reed switch at any home improvement store. Another simple method is to use one of these. Just remove the LED and use it with an opto-coupler as a switch for an audible alarm. Personally I like just wrapping several turns of the line around a magnetic reed switch.

Ron

 

[Nigel Goodwin]

Hi, thanks for that, I have found your circuit here: https://www.electro-tech-online.com/threads/question-regarding-amperage.154766/page-2#post-1335300

Only worry is a 175 W incandescent bulb will have a high turn on current from cold, so would this make choosing a suitable series resistor value to work, yet protect the TRIAC on turn on tricky? I like it's elegant simplicity though, thank you.

Well done finding it - I failed!.

It shouldn't be at all tricky calculating the resistor value, the surge of the lamp shouldn't be a problem either as it's so brief, and thyristors are very sturdy devices, the series resistor to the gate offers protection for it. I've no idea what current the original was rated for, as I never saw the fan it was feeding, but in that case, just as in yours, the current is fixed and well known, allowing easy resistor selection.

I agree about it's elegant simplicity, but I just drew it out from a commercial product

If you've got a suitable thyristor knocking about throw one together and give it a try, you don't even need a relay for testing it - just stick another lamp in as a load

 

[ronsimpson]

I have a box full of remote switches from Sonoff. I have not tried this one yet. This type not only allows you to turn on/off the switch from your phone but also tells you how much power the light is using. 0 power=failed bulb. It uses your wireless network!

I have used the TH16 version and it tells the temperature and humidity. (includes a timer and thermostat)
Just a thought. Ron S.

 

[Nigel Goodwin]

I have a box full of remote switches from Sonoff. I have not tried this one yet. This type not only allows you to turn on/off the switch from your phone but also tells you how much power the light is using. 0 power=failed bulb. It uses your wireless network!

Nice, I've not seen that one

 

[Reloadron]

I have a box full of remote switches from Sonoff. I have not tried this one yet. This type not only allows you to turn on/off the switch from your phone but also tells you how much power the light is using. 0 power=failed bulb. It uses your wireless network!
View attachment 121898
I have used the TH16 version and it tells the temperature and humidity. (includes a timer and thermostat)
Just a thought. Ron S.

That is really slick for the buck. Thanks for putting it out there.

Ron

 

[unclejed613]

Are we looking at dust iron material toroids here?

since ferrite material varies widely in characteristics, it's something you may have to experiment with. the easiest bet would be using an input filter choke from a switching supply which are often toroids. there are already two windings there you can use as a secondary (use one of them since they are wound in opposite directions), and all you have to do for the primary is run one of the wires to the lamp through the middle of the toroid.

 

[ronsimpson]

That is really slick for the buck.

In the chicken house and in the dog house I am using the TH16 (or TH10) in thermostat mode. Chickens = 46F and dog at 43F right now. I can see it from anywhere I can get the internet. Next I am going to get some network wall switches.

 

[AnalogKid]

Starting with Nigel's circuit, I would replace R1 with two diode bridges in series. This will give a constant "operating voltage" independent of the load current, probably around 3.2 V for a 1 A load. I just happen to have a bunch left over from past projects, so it's a junk box project. Here is a similar part from a US distributor; I'm sure there is something similar in the UK.

TS4K40-A Taiwan Semiconductor Corporation | Discrete Semiconductor Products | DigiKey

Order today, ships today. TS4K40-A – Bridge Rectifier Single Phase Standard 400 V Through Hole TS4K from Taiwan Semiconductor Corporation. Pricing and Availability on millions of electronic components from Digi-Key Electronics.

www.digikey.com

Another possible change is to replace the TRIAC and relay with an optocoupler. The output will pulse at 60 Hz, but an RF remote module almost certainly won't care. If yours is cranky, add a 4.7 uF cap across the C-E output.

ak

 

[alec_t]

I am into amateur radio and the junk box may produce something. Are we looking at dust iron material toroids here?

Don't think it's critical. I've even used an old shaded-pole mains motor as a current transformer.

The blue wire is mains neutral, which goes the scenic route around the motor core a few turns.
(The fan-heater was just a test load).

 

[unclejed613]

wow, that's a pretty good solution... those motors are very common

 

[dr pepper]

If you dont want to build any electronics you might be able to re appropriate one of these 4 way extension sockets whereby one of them plugs into the tv, and when the tv is turned on it senses it and turns all the other sockets one for the dvd etc, then you'll have a circuit that closes a relay when a load is present, if your licky said relat may have a normally closed contact which is all you then need.
One of the elektor articles shows a couple of similar circuits, one a similar idea to the motor, but uses a transformer, and the other just puts 3 diodes inline with the load, then detects the vdrop across the diodes when the detected device draws power.
I've seen devices designed to do almost exactly what you need for marine navigation lights, a relay closes when the filament fails, but everything is led now so you wont find one of those.

 

[gary350]

It was used in a school to monitor an extractor fan that was used to remove potential Radon gas build-up.

Radon gas is a joke depending which part of the country you live in. When we tried to sell our Tennessee house 1 out of state buyer wanted the house tested from Radon. Realtor never heard of Radon after some research she figured it out. State of TN gives out free radon test kits so we got one. House had been empty for months so it flunked the Radon test. After reading EPA information the information is guess work. Know one knows what a safe limit for radon is so EPA made up a number .000000000000004 parts per million or less is safe. EPA explains about Radon it is a natural gas that comes from rock it never builds up in a typical house because people come and go all day every day this allows the gas to escape. A empty house will test high for radon because radon is never allowed to escape. EPA cure for high radon in a house is, open all the doors and windows to allow air to blow through radon will be gone. EPA also says, a house the granite counter tops will test higher for radon than a house with no granite counter tops. EPA also says front and back yard will test equal or higher for radon than the inside of the house. In Tennesse once a house is RED FLAGGED for radon it must be noticed on the realtor list for all other buyers. This started a snow ball effect all new interested buyers wanted to know what is radon when they were told it is believed that maybe it can possibly cause cancer but no person has ever been known to get cancer from radon. This made the house impossible to sell in so we took house off the market for 2 years. After 2 years it is no longer required by law to tell buyers house tested .000000000000005 for radon. We relisted house and made sure to let radon out every day doors were open 20 minutes in the morning and 20 minutes in the evening. Only 1 out of state buyer wanted a radon test and it passed. That was 8 years ago. Sense then EPA has revised all their online radon information. We moved to Arizona and found a house to buy. I decided to ask realtor if house will pass radon test, she busted out laughing. She said, what a hoax NO house in AZ will pass a radon test, radon in front yard is 2 times higher than what EPA allows you probably can not find a house in any of the western states with rock that will pass the radon test. After living in AZ 3 years we moved back to TN. If you want to kill the sale of someones house ask for a radon test. LOL. We had investors offer us $100,000. less for our house because if flunked the radon test. LOOK OUT for the sneaky snakes.

 

[Nigel Goodwin]

Radon gas is a joke depending which part of the country you live in.

Radon is only a possible problem in certain types of geographical area, and the worst area is obviously cellars (basements) if you have them - so the only place any testing is done in the UK is in areas where it's a risk, otherwise there's no point.

 

[Reloadron]

Radon is only a possible problem in certain types of geographical area, and the worst area is obviously cellars (basements) if you have them - so the only place any testing is done in the UK is in areas where it's a risk, otherwise there's no point.

Same here in Ohio. My parents bought their house in '66. My sister now owns it. The only place Radon Gas builds up is the basements and where this house sits it is all shale. Now by code all houses, before sale, must be tested and once tested they install blowers vented to the outside. Here is an interesting coincidence. My father died in '99 at age 77 of pancreatic cancer. He spent countless hours in his basement wood working after his retirement. Several neighbors also died of cancer all about my dad's age and all men who spent quite a bit of time in their basements. We just attribute it to weird coincidence but some believe in other families that it was a result of exposure to radon gas. Anyway, yes, it is a heavy gas and only settles in basements where the air isn't moving it out.

We now resume our regular forum:
Circuit to give an RF remote audible indication of a mains bulb failure

Which radon gas won't do.

Ron

 

[dr pepper]

I messed with a gizmo to measure radon a while back, it sucks air through a filter mesh, then said mesh is checked for radioactivity, theres a full webpage on how to make all the gizmo's required.
Radon isnt particularly harmfull, its radon daughter gases that are harmful, from memory a couple are polonium & lead, both are also radioactive.