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Current activated relay with timer

Discussion in 'General Electronics Discussion' started by Peter Euston, Sep 7, 2016.

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  1. Peter Euston

    Peter Euston

    3
    0
    Sep 7, 2016
    Hello everyone, I'm trying to build a 'device' with a current activated relay and timer.
    My aim is to provide a safety device so the elderly can't run the microwave oven for too long and potentially set fire to the place.

    There is available a spring tension, push button timer but my concern with this is that it requires 2 actions to make the microwave work which is beyond the mental capacity of some people.

    What I'd like to offer is a current activated relay/switch that clicks in as soon as the microwave is turned on. This part is not a problem. What I need to do is incorporate an adjustable timer set to say 6 minutes so that the power to the microwave will be cut of after the 6 minutes even if the microwave was programmed for longer.

    I hope I have explained myself and my idea properly.

    Many thanks.

    Peter Euston.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
    2,788
    Jan 21, 2010
    There are both hall effect and inductive current sensors available which can detect AC current in a conductor.

    The magic words you might use in your googling is "current transformer".

    Microwave ovens will generally stop if you interrupt the power, so this world be a sensible way to reset the oven.
     
  3. oz93666

    oz93666

    38
    1
    Dec 7, 2014
    I think you might be overreacting ... My understanding is there's no possibility of a microwave oven starting a fire , the way it works it just cannot reach dangerous temperatures ... worst scenario is the food is overcooked ...

    Try a few experiments to put your mind at rest ...or perhaps look for an oven that is easier to operate , they're very cheap.
     
  4. Peter Euston

    Peter Euston

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    0
    Sep 7, 2016

    Hello Steve and thankyou for your reply. The particular case I was concerned about was of a woman who put a Wheat-bag in the microwave to warm it, set it for too long a period then went off and forgot all about it. The wheat-bag was severely blackened and had to be thrown out.
    There is a possibility that the Aged Care Services may intervene if we cannot find a way to limit the time a microwave will operate unattended.

    Many thanks.
    Peter.
     
  5. Bluejets

    Bluejets

    4,258
    907
    Oct 5, 2014
    Why cut-in to the circuit, only need to plug microwave into a timer. Plenty of them around. Reset at each operation.....easy. Plus no pensioner is going to be able to re-program the timer, they will need a four year old for that. :)
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
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    Jan 21, 2010
    I think the idea of a simple device which monitors the current and interrupts the power if it has been drawing (say) > 1A for more than 4 minutes is a good one. However, what happens if the microwave is set for 75% power and is effectively off for 5 seconds in every 20? That may require some additional logic.
     
    Peter Euston likes this.
  7. Peter Euston

    Peter Euston

    3
    0
    Sep 7, 2016
    Hello everyone, I'm looking to make an electronic device to control the operation of a microwave oven for use by a forgetful senior citizen.

    What I would like to do is to time a current activated relay so that when ever the microwave is programmed to heat/cook something it will run for no longer than a set time...6 minutes would be ideal. The issue has been that a wheat bag has been put in the microwave to heat and even though 2 to 3 minutes is ample it was set for a long period, then forgotten about, until it burned.

    Rather than stop the forgetful elderly from using the microwave I would like to install a current activated relay that would allow the microwave to work regardless of the time it was programmed for. That is the easy part.

    Once the microwave is operating I would some how like to have a timer, set for 6 minutes , turn off the microwave so that nothing can be inadvertently over heated to the point of burning.

    I'm hoping that some of you very savvy electronics experts might be able to point me in the right direction.

    Many thanks.
    Peter Euston.
     
  8. Alec_t

    Alec_t

    2,902
    784
    Jul 7, 2015
    Googling 'countdown timer switch' should find you something.
     
  9. Tory Cooper

    Tory Cooper

    1
    0
    Nov 7, 2016
    You can always buy a programmable timer. I just used one in a under cabinet lighting project of mine and it works great. I found it easy to program and it works for a bunch of different timing applications. Coupled with a relay and supplied with the proper voltage and you can make it delay on, delay off or time for just about any length of time. You can find one at the link below...

    http://www.3rdbrakeflasher.com/timer-c-68/

    I used mine with a touch sensor and a12 volt power supply and set it for 15 minutes. I've times it and it's right on time.
     
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