How do I use a light to tell me when a heater opens?

Discussion in 'The Projects Forum' started by bill5335, Jun 7, 2013.

  1. bill5335

    Thread Starter New Member

    May 25, 2013
    I am looking to wire up a neon bulb to light when a heater has failed.

    We have several heaters and need a way to tell the operators when a heater fails. The heaters become an open circuit at failure.

    I am thinking of wiring the bulb (and resistor 200kΩ?) in parallel with each heater. Each heater draws 0.6 amps

    My thought is, when the heater is working (they are about 300 ohms) the current will flow through the heater which presents a lower resistance, bypassing the neon bulb.

    When the heater fails (opens up) the light will come on.

    Does this sound like it will work? It seems like my light will be on even when the heater is working. Not sure what I am missing.

    I apologize for not posting a schematic.


  2. crutschow


    Mar 14, 2008
    Your scheme won't work since the voltage across the bulb is essentially the same whether the heater is working or open, only the current changes. You thus need some way to sense the current in the heater.

    What is the supply voltage and is it AC or DC?
  3. circuitfella11


    May 10, 2013
    one case would be the bulb be not bright when the heater is working, and when it fails the bulb becomes brighter, indicating full current flowing through it.. this is how i see it..

    just like crutschow said, sensing the current would be better..
  4. Externet

    AAC Fanatic!

    Nov 29, 2005
    :) Feed one heater supply wire trough the hole, and the LED will be on when the heater is working.

    If not on, circuit is open:



    Simpler than that; connect a green neon across the power switch, (points A & B) will show the heater is healthy but only when power switch is off, like signalling "Am healthy, ready to heat up if you turn me on"


    This way would take a momentary manually and briefly turning the switch off to confirm the green signal of heater health. If the switching is automated or by a relay, you would need to insert a normally closed momentary push switch to read the heater health.
    Last edited: Jun 8, 2013
    bill5335 likes this.
  5. bill5335

    Thread Starter New Member

    May 25, 2013
    Thanks Externet.

    I think the current sensor you linked to will be the easiest solution.

    The supply is AC.

    Thanks to all that replied.