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Thermo resistor safety switch

  1. Jul 28, 2015 #1
    Good day , could someone please point me to a device that would have say two wire terminals and could interupt the flow of current between them when a dangerous temperature is reached?

    the idea is simple , I built a lamp and I need some failsafe mechanism that would turn the lamp off when it gets too hot.the lamp is powered by a ordinary PC power supply.So normally I just connect the green wire to any of the black ones (ground) and the psu starts to work and the lamp shines, I would like to have thios switch attached to the lamp surface and connected to those green and black wires so that when the temp is high enough the current would be interrupted and the psu would shut down.

    I have seen such devices in car amplifiers were they are attached to the aluminum heatsink and work as a fail safe so that when the temp on the heatsink gets too high the amp shuts down.

    I hope you understood my quest , would be glad if someone could point me to some possible devices to use, thanks.
     
  2. jcsd
  3. Jul 28, 2015 #2

    billy_joule

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    A thermal cutoff is what you're looking for
    https://en.m.wikipedia.org/wiki/Thermal_cutoff

    They come in a range of current and temps. All electronics suppliers will have them, some for just a few cents each.

    You should re think your design. A lamp should not need a thermal cut out.
     
  4. Jul 28, 2015 #3

    Hesch

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    Gold Member

    Well, you could use some NTC-resistor + opamp + transistor.

    But what about a bimetal switch?

    China_bimetal_thermal_switch_for_heater_and_motor20125292039182.jpg

    I don't know if the lamp must be kept switched off, when switced off, but you can make this function by means of a relay.
     
  5. Jul 29, 2015 #4
    well ideally it would have to work like this, if the temp in the room gets too high and the lamp has the potential to overheat the switch shuts it down but only for as long as the lamp is too hot , once the temp goes below the threshold level it should kick back again.
    much like the portection of a car audio amp once the aluminum radiator is too hot it shuts down then after it cools off it kicks back in.
     
  6. Jul 29, 2015 #5
    Hello Sal - Really 2 and 3 are the same thing - there are cutoff switches in both NO and NC, that can handle a typical lamp load - you want a NC type and need to determin the temp you want to turn the Lamp off at, and then the voltage and current of the lamp. LINK
     
  7. Jul 29, 2015 #6
    well the temp would be around 100 degrees celsius , but i dont intend the swith to cut off the current to the lamp rather just the current that passes in the green to black wire from a pc psu. my lamp is powered from a pc psu so i can shut it down disconnecting the green wire from the earth of the psu, I search for such a device.
    Also I dont need a thermo fuse like in transformers which when blows has to be changed but rather a switch like in amplifiers which disconnectes when too hot and then after the temp has decreased kicks back in.
    I will try to look up something myself but if you have some links handy feel free to post them , thank you.
     
    Last edited: Jul 29, 2015
  8. Jul 29, 2015 #7
    A thermostat sounds like what you want.
    They come in different kinds, the simplest being based on a simple bimetalic strip are very cheap.
    They are used routinely for applications such as controlling electric oven temperature, water heaters and so on.

    Googling 'thermostat' gave me hundreds of leads to various devices and several dozens of potential suppliers
    (You might even be able to get a useable one out of old electrical junk if there is a dump for that kind of thing near you).
     
    Last edited: Jul 29, 2015
  9. Jul 29, 2015 #8

    billy_joule

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    What exactly are you trying to protect?
    Thermal cut outs aren't used in lamps, there is no need.
     
  10. Jul 30, 2015 #9
    there is if you have little more than 100 pieces of 2watt LED's mounted on a aluminum plate.
     
  11. Jul 30, 2015 #10
    Perhaps instead of a power cutoff when thing get overheated, you could add a simple cooling system to the aluminium plate so that it doesn't overheat ?
    Just some heat radiating fins might be enough, if not you could add a small fan as well.
     
  12. Jul 30, 2015 #11
    I already have active cooling with the help of 3 pc fans. I want the thermo switch simply for failsafe safety reasons.
     
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