I have several reptile enclosures and I use ceramic heaters (they don't emit light in the visible spectrum) so I am asking for help to build a circuit that when the bulb 'burns out' it would turn on a LED or something visual to indicate a non-working heat element.

I was thinking maybe something like this:


Thanks for any / all input,
Rod

 

The problem with that circuit is the relay coil will take most of the voltage, leaving little for the heating element.

You could use a small current transformer to directly light the led.
Here's a Youtube video on how to make one.

 

The problem with that circuit is the relay coil will take most of the voltage, leaving little for the heating element.

You could use a small current transformer to directly light the led.
Here's a Youtube video on how to make one.

Although I like the simplicity shown in the video, I was more hoping for a indicator that comes on when the element goes bad.
Were I to follow the method shown, it would have 8-12 LED's on 24/7 (The main reason we use non-light emitting heaters is because when his snakes have babies & we separate them into separate enclosures & with standard light bulb style heaters he couldn't sleep from too much light).

 

If you wired the relay coil in parallel with the ceramic heater instead of in series with it, I think then that the heater would draw most of the current when it was working, starving the relay for current and keeping it in inactive. Once the heater failed, the full voltage would be applied to the relay coil, energizing the relay. In the case you'd want to use the NO relay contacts instead of the NC contacts.

I'd need to know the specs on the heater and look at relay coil specs to feel more confident, but an educated guess is that this should be feasible.

Size:75W 110V
Specifications
Material: Ceramic + Alloy
Color: Black
Diameter of heating surface: 8cm
Height: 9.5cm (Approx)
Wattage: 100W 110V
Life span: Up to 10,000 hours
Heating source: Ceramic, infrared, electrical, no light emitted
https://www.amazon.com/gp/product/B00PS4YD1A/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

 

Putting them in parallel won't starve the relay of current. Both heater and relay coil will see the same full mains voltage and draw their respective rated current.
I like the current transformer idea. You could easily make one.

 

Use a simple opto-coupler and series diodes volt dropper to detect the ac current in your heater, as long as the heater is on the opto-coupler is on and led will be off, if the heater stops led will light up, put your led across the output of the Q1 C/E terminals with a 1k resistor, and use 5/12v dc supply...

Use 1N54007 diodes for D1,6

 

If you take Dodgydave's circuit in post #7 and modify it by putting the capacitor from collector to ground (instead of to +5) and then put your LED across Q1 and you will have an LED that comes on when the current stops flowing.

You can also get the same effect by using crutscow's idea of using a current transformer if that is easier for you than finding an optical coupler. Just feed the output of the current transformer through a resistor (1K or 2K for starters); connect the emitter to ground; connect the collector to a capacitor and the anode of an LED with the other terminals of the capacitor and LED to ground; and then run a 1k resistor from +5 to the collector.

In both cases I would make the capacitor 47 uf to assure that the LED does not glow dimly while the heater is connected and working.

 

Here's another option, using a current transformer :-


... or a simpler version :-

 

Putting them in parallel won't starve the relay of current. Both heater and relay coil will see the same full mains voltage and draw their respective rated current.

Yikes! Sorry. I really do know better than that. I was posting last night when I should've been asleep already. Wasn't thinking clearly.

 

If all you want is an indication of a burned out element these little units should work fine, unfortunately they are On with current flow rather than off but the emitted light is negligible. The current carrying conductor can be loped multiple times as needed and seen here. They are self powered so really nothing much is required other than running your current carrying conductor through the doughnut. The link are a few examples but this type indicator can be found just about anywhere from assorted manufacturers I would guess. They can be had from a few suppliers for about $10 USD each give or take.

Ron

 

You could use a 'klixon' thermal switch that senses the heat of each element and if it 'burns out', will turn on a warning lamp when the heater fails, if you want the indicator 'ON' for failure.
There is many types and temperature ranges.
----> http://www.carbonbrush.com/klixon7bt2.jpg

Or , this type, preselected for 30C ----> https://www.aliexpress.com/wholesal...70814090315&SearchText=30c+bimetal+thermostat

I do not understand the stupidity of naming them 'normally closed' or 'normally open' *
Should be closed above/below rated temperature or open above/below rated temperature.
You want closed below rated temperature.

* Can anyone explain the rationale ?

 

You can always monitor temperature. Here's fancy system if your really concerned. http://www.thermoworks.com/ThermaQ-WiFi

You can also look at freezer alarms: http://www.thermoworks.com/search?keywords=freezer alarm

I don't like the RT8100 because I need to monitor fridge/freezer that I don;t use every day. The alarms are not loud enough and no external contacts are required. It does log how long the problem occurred. To see the light, you have to look at it.

The suction cups suck for use in the fridge. It's, nonetheless a thought.

 

Were I to follow the method shown, it would have 8-12 LED's on 24/7

You could mount the LEDs well away from and outside the enclosures
If you restrict the LED current so they are just dimly lit, I wouldn't think that would bother the snakes.

 

You could mount the LEDs well away from and outside the enclosures
If you restrict the LED current so they are just dimly lit, I wouldn't think that would bother the snakes.

hehe,
it doesn't bother the snakes, it's my son's room. he is the budding "reptile vet" and "I can't sleep with a light on" person...
I am just the hired help who makes things work.