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Electric kettle that shuts off when boiling

  1. Jul 26, 2010 #1
    Electric kettle that shuts off when boiling....

    How does it do it?!

    I bought one this weekend and I think it is really cool....but I wonder how it does it. My guess is that it has some pressure sensor that detects the difference when the water is boiling....but I really wonder about the details of it even if that is the case. Does anyone know about it?

    Here is a picture of the kettle:
    best-electric-kettle-capresso-h20-plus.jpg
     
  2. jcsd
  3. Jul 26, 2010 #2
    Re: Electric kettle that shuts off when boiling....

    OR maybe there is some sensitive switch in the handle that is activated by the steam?
     
  4. Jul 26, 2010 #3

    turbo

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    Re: Electric kettle that shuts off when boiling....

    pressure switch or thermocouple. Anything higher than 100C has to be steam at low pressure.
     
  5. Jul 26, 2010 #4

    Danger

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    Re: Electric kettle that shuts off when boiling....

    Intriguing question. I know that I read up on the subject once, but I can't remember it. It used to be that I assumed a thermostat to be involved, but that wouldn't work unless the appliance was regional-specific. Boiling point varies with altitude, so a kettle calibrated for Denver wouldn't even think of boiling in Miami. The pressure increase, however small, might do the trick. I know that mine won't trip if the lid is open, which I consider an argument in favour of that theory. The best thing that I can recommend is to visit "HowSuffWorks" on the net. It's one of my favourite sites. Anything from a tennis ball to a neutron bomb is dissected and explained, with cool pictures. I'll look it up my own self later on, but for now I have other things on my mind.

    edit: Turbo, how the hell is it that you always manage to sneak in ahead of me?
     
  6. Jul 26, 2010 #5

    turbo

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    Re: Electric kettle that shuts off when boiling....

    There's an alien culture that has showed me how to "slip" time just a bit (they won't show me how to go WAY back). It's an "edge" given to friendly humans.
     
  7. Jul 26, 2010 #6
    Re: Electric kettle that shuts off when boiling....

    I think I bought the kettle from them:tongue2:

    Thanks so much Danger and turbo!
     
  8. Jul 26, 2010 #7

    dlgoff

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    Re: Electric kettle that shuts off when boiling....

    I'm thinking it just has a timer that is set to a time that will guarantee a full pot gets boiled.
     
  9. Jul 26, 2010 #8
    Re: Electric kettle that shuts off when boiling....

    The only problem I can think of if they manufactured it that way, is the use of it at higher altitudes....people would really get annoyed if the pot kept shutting off before the water boiled. But really it is cool, as soon as the water comes to a boil it shuts off immediately!
     
  10. Jul 26, 2010 #9

    dlgoff

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    Re: Electric kettle that shuts off when boiling....

    Well maybe it's got an altimeter that adjusts the timer. :devil:

    But if it shuts off immediately then it's probably not a timer.
     
  11. Jul 26, 2010 #10
    Re: Electric kettle that shuts off when boiling....

    perhaps it monitors temperature rise, and shuts off when delta-T reaches zero.
     
  12. Jul 26, 2010 #11

    Evo

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    Re: Electric kettle that shuts off when boiling....

    No, I have a couple, as soon as it comes to a full boil it shuts off. About 30 seconds for 2 cups, up to 1-2 minutes for a full pot.
     
  13. Jul 26, 2010 #12

    dlgoff

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    Re: Electric kettle that shuts off when boiling....

    Can you take it apart and let us know what type of sensor it's using?
     
  14. Jul 26, 2010 #13

    mgb_phys

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    Re: Electric kettle that shuts off when boiling....

    They mostly use a bimetalic switch, most of them invented by this guy http://en.wikipedia.org/wiki/John_C._Taylor_(inventor [Broken])
     
    Last edited by a moderator: May 4, 2017
  15. Jul 26, 2010 #14

    BobG

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    Re: Electric kettle that shuts off when boiling....

    Just about all of them have an overtemp fuse, which a bimetalic switch would be appropriate for, but water boils at different temperatures depending on the altitude.

    I think it has to be a pressure switch, since there's definitely a pressure change when the water boils - which is why the whistling tea kettles whistle when the water boils. Except the opening for the steam is partially blocked for the whistling tea kettles, allowing pressure to build up.

    Check the opening of the spout. If it even has a light flap covering the spout, then there should definitely be enough pressure to activate a pressure switch (and maybe even if the spout is open provided you started with enough water). The kettle just has to heat the water faster than the steam can escape.

    The danger would be if you turn the pot on with so little water that it doesn't build up enough pressure to activate the switch. Some of the better pots have a sensor to detect the pot is dry as a safety measure while others just assume having the kettle turn off as soon as the water boils is good enough, since the thermal fuse will open if the temperature gets too high.

    The switch to turn off the pot when it's dry would be more interesting. Unless it's really just the thermal fuse. As long as there is water in the pot, the water can't get above boiling and it will carry off excess heat from the metal or glass. The only way the metal or glass can get much above boiling is if the pot is dry. In other words, both variations could work the same way, except they give it different names.
     
  16. Jul 26, 2010 #15
    Re: Electric kettle that shuts off when boiling....

    cutoff when dry is already a common feature in coffee pots. when the water is all perked out, the element will overheat, which should be simple enough to control.
     
  17. Jul 26, 2010 #16
  18. Jul 26, 2010 #17

    lisab

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    Re: Electric kettle that shuts off when boiling....

    Mine clicks twice: once when it reaches boiling, then again about 15 minutes later when it cools down (after it's empty). Both clicks sound very similar.
     
  19. Jul 26, 2010 #18

    Evo

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    Re: Electric kettle that shuts off when boiling....

    It doesn't turn off when it starts to boil?
     
  20. Jul 26, 2010 #19

    lisab

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    Re: Electric kettle that shuts off when boiling....

    Oh yes, the first click is when it turns off, about 10 seconds after it starts boiling. The second click...I have no idea what it means, except the kettle has cooled off a lot.
     
  21. Jul 27, 2010 #20
    Re: Electric kettle that shuts off when boiling....

    Wiki says that they use a bi-metalic switch that bends and cuts off the electricity when the steam warms it up. That explains lisa's double click.
     
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