Please help me design a auto turn off switch for a kettle...

Discussion in 'The Projects Forum' started by timez, Nov 4, 2011.

  1. timez

    Thread Starter New Member

    Mar 21, 2008
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    Hi,

    I know i should be doing my own research on how to make this - but i tried before (with a thrmister and a relay) but failed.

    The kettle is very unsafe at the moment as it does not switch off when it boils.

    Its very easy to forget it is on because as it boils it goes silent (the water i mean)

    It runs on 230 Volt mains electricity.


    I have timed the amount of time it takes to boil the kettle with the usual amount of water in it -

    Exactly 3 Minutes...

    Can I maybe make a timer that will switch the mains source off at that time?

    something like this...


    (where it says wire - thats the wire thats from the plug to the kettle (both sides of the 'timer') that is already part of it)


    MAINS -> WIRE -> TIMER -> WIRE -> KETTLE

    the reason for that is so any circuit is not inside the actual kettle where it could get wet (even covered with plastic).

    what i need help with is how do i make the timer that can count 3 minutes and then switch mains electicity (230-240 V) off and stay off until the wall switch is turned off and on again - but will then reset itself when switched back on at the wall.

    I was thinking maybe putting a latching relay as the on/off/on part.

    (it doesnt HAVE to be a timer if anyone has a better idea)

    I was thinking maybe using a 555 timer chip (or simular) to switch a transister to switch the relay - but i dont know how to actually put that together (without some help)


    If anyone could help me do this it would be a life saving event (or at least a kettle/electricity saving event anyway lol!)


    --- Sorry for the all over the place post ---

    Thank you for any help anyone could offer.

    Timez
     
    Last edited: Nov 4, 2011
  2. JDT

    Well-Known Member

    Feb 12, 2009
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    Timer is one way.

    Actual automatic kettles have a temperature sensing device not in the water but in a place where the steam can escape. It detects the presence of steam, not the water temperature. Often the measuring device is a simple bi-metal strip.

    Personally, I would buy a better kettle (how expensive are they?).
     
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Last edited: Nov 13, 2011
  4. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Why mess with building a timer to turn the mains off in three minutes when you should be building an timer to create an alarm to tell you to get yourself back to the kettle!

    Or simple buy a kitchen timer to alert you.
    Or simple buy a better kettle.

    I would say buy a timer/outlet and plug the kettle into it, but most of them are probably not designed to handle the current required by your kettle.
     
  5. timez

    Thread Starter New Member

    Mar 21, 2008
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    Well for 1) im trying to learn electronics - and i thought this would be a good project.

    2) I cant afford a new kettle.

    3) an alarm is ok - but its not great - id rather just make a timer.


    -- thanks for ignoring my original question - i didnt say - should i do that.. i said - how can i make that?...

    If anyone wants to actually answer what i asked - without judgement - please feel free to help...

    Thank you

    timez
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Meddling with mains while learning is not encouraged in this forum

    You should learn starting with low voltages or start with this
     
  7. timez

    Thread Starter New Member

    Mar 21, 2008
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    0
    well as you have probabbly guessed im going to anyway - so even though it isnt encorouged - what your basiclly saying is - we aint gonna help you - basiclly forcing me to take the more dangorous option.

    Thanks anyway

    Timez
     
  8. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Nobody is forcing you to do anything. If you choose to meddle with things that you have admitted not knowing much about, that is your responsibility. You might like to think about the likely costs of a cheap automatic kettle, your timer project, and the cost of an accident that might result from getting this wrong.

    When last I looked, you could get a cheap kettle for less than £10 in our money. A funeral would cost thousands.
     
  9. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Wow ! that's some attitude you got there Mate.

    What you do is up to you. We or I will not, I repeat, will not help you in doing anything with main supply voltage since you are beginner. Chances are that you might get electrocuted. I can't have that on my conscious.

    I did show you something you could learn. If you have done that, then we would have shown you how you should handle mains.
     
    Last edited: Nov 21, 2011
  10. timez

    Thread Starter New Member

    Mar 21, 2008
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    0
    Its because i didnt ask for a judgement on whether i should or not - i asked how to do it - a simple question that i wanted at least an answer to (even if it isnt simple) yet no-one wants to answer it.

    Well yeah ok ill just do it all on my own,

    I wont electrucute myself - in fact ill prob manage to do it - but i was hoping to save some time before the constant boiling kills the kettle.

    you all seem to think the safer option is to say "dont do anything with the mains" knowing full well im going to.

    so whats really safer?

    leave me to my own devices and hope i dont do anything mad.

    or actually help me, knowing at least some people who know what they are doing might be able to make it safer for me by helping me.


    Seems the 2nd option is a no brainer - but i guess no-one see's that.

    well ok - guessing it is then

    Timez
     
  11. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    U should start with the low voltage circuits first.

    The actually switching will be done via a relay, so u will be safe and when u are ready to plug in the kettle, we'll know.

    Let's start with the basic timer config, shall we ?
    If you want to make something, tell us what u have and how much are willing to spend.
    Remember learning and building will be more than buying a kettle.
     
  12. iONic

    AAC Fanatic!

    Nov 16, 2007
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    In all honestly, I'd have this thread locked up by now.
     
    Last edited: Nov 14, 2011
  13. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    @timez

    Bear in mind that there is no obligation binding the AAC members to answer your query. Especially if they feel that your project can turn to be unsafe for you and your family.

    Are going to judge them for being considerate and responsible enough not to give you potentially harmful information? I would characterize this stance as well-thought and protective.

    What isn't well thought is to try to extract answers by emotionally blackmailing other people. That will not do.
     
  14. timez

    Thread Starter New Member

    Mar 21, 2008
    7
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    I know - im sorry i went off on one.

    and im not sure - at the moment i have a 555 timer chip (but i dont know if it can be used for something like this)

    Also i wasnt sure if the 555 can handle 230 V (does it need to - to switch the relay?)

    I also have loads of resisters and a few capacitors - and wires etc obv lol

    And i have some protoboard i was gonna put it all on, im doubting the protoboard could handle the amount of volatage itself though.

    Timez
     
  15. Adjuster

    Well-Known Member

    Dec 26, 2010
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    The 555 is strictly a low-voltage DC device, as you would know if you had looked up its data sheet. It could, in principle, be used to operate a mains-voltage relay. If the relay required more current or voltage than the 555 could safely provide, it could be driven via a bipolar transistor or FET.

    Proto-boards are not suitable for mains voltage working, certainly not at the current drawn by a kettle. For instance, a 230V 2kW kettle takes 8.7A! Personally I would not even like to see a proto-board project even controlling a mains relay: the whole set-up is too fragile.
     
  16. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Most everything will need a low voltage power supply to function, such as thermistor circuits, 555 timer circuits, etc.

    Then they run a relay (or a Triac) to enable/disable the line powered item. This includes most modern appliances, hot pots, microwaves, etc. Most everything has a 5V or 12V side, and a 120/240V side.

    I'm not trying to discourage you, there's just a bunch of ways to do it simply with a power supply, while there isn't any easy way of doing it all with line voltage alone, if that makes sense.

    A 555 timer run off a 5VDC adapter would work to trip a relay easily, and with few parts. See Bill Mardsen's blog posts.

    A more complicated and exact method is to measure the temperature of the pot, and when it stops increasing, the water is boiling (no need to know exact temp, just if the temp is increasing).
     
  17. timez

    Thread Starter New Member

    Mar 21, 2008
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    I think i may have overestimated my capabilities on this one, in my mind it was relativily easy - get the 555 to time so many minutes then switch off the kettle with a relay - but i have a feeling im gonna either fry the 555 - or melt the protoboard.

    Its a real shame because all the parts that used to work the kettle are still in there - its just my mums ex was a bit heavy handed and broke the switch - thing is - i cant actually see anything wrong with it from opeining it up.


    Do you maybe think a better option would be to try and fix the switch?

    Maybe even posting some photos of what the insides look like - im sure you would be able to work out the problem more easily than me if you could see it.

    Any thoughts?

    Timez

    P.S. - thank you for still trying to help me even tho i went mad at you all - i feel really bad about that now.
     
  18. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Yes, if you post hi resolution, clear photos of both sides of the circuit board and wiring, in addition to parts of the switch, if you can locate them, we can help you get it working again. Biggest problem with pictures is flash bounce washing out the details. Best way to do it is take the pictures outside on a sunny/slightly overcast day so there is no flash.

    Everything from Christmas lights to TVs have been fixed/improved on this forum in that manner.
     
  19. timez

    Thread Starter New Member

    Mar 21, 2008
    7
    0
    ok ill try do that, pretty sure the laptop cam ive got is HD.

    Also i cant wait to see the looks i get from the neighbors being outside photographing a broken kettle - haha.

    Timez
     
  20. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    no worries timez.

    Here in AAC, we are here to help. So we don't really get mad or offended. I hope this is how every member of AAC feels.

    If we step out then who will be there to help.
     
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