how does this thermostat work?

Discussion in 'General Electronics Chat' started by zenite, Dec 30, 2009.

  1. zenite

    Thread Starter New Member

    Dec 21, 2009
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    I am looking into using FK934 for my project but am wondering how it works. My project involves building a cooler using the peltier effect. I want to use the FK934 to control the temperature of the cooler. If the temp. is cooled to the temp. set on the thermostat, the power supply will cut off. When the temp. increases, the power supply will kick in to cool it back.

    Can anyone advise on how I can do this with FK934? There doesn't seems to be a display screen, so how do I set the temp.?
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Do you hav a link to some more data on this FK934?
    Without this we can not help you.

    Greetings,
    Bertus
     
  3. zenite

    Thread Starter New Member

    Dec 21, 2009
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  4. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    We need the schematic. Do you have a link?
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Unfortunately there is no "manual" for download on the pages.
    I will have to guess how it works.

    [​IMG]

    I hope I am right and you can do something with it.

    Greetings,
    Bertus
     
  6. zenite

    Thread Starter New Member

    Dec 21, 2009
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  7. Wendy

    Moderator

    Mar 24, 2008
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    Using AC like it does it isn't standardized. Most modern thermostats use a transformer to use low voltage AC.

    The relay is the component most likely to wear out over time. It will take years, but it will eventually go.

    The rest of the parts could last a very long time, but lots of bad things can happen to them over time, mainly involving static electricity. I've seen commercial units last decades, but had others (in my house) go after a couple of years. There is an element of chance in this.
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    In the schematic there is this picture drawn:

    [​IMG]

    The small pot sets the range and the large is a fine adjust.
    There is indeed no display.

    Greetings,
    Bertus
     
  9. zenite

    Thread Starter New Member

    Dec 21, 2009
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    I am not quite sure what is the power supply like. Is it 12VDC or 12VAC? The diagram puts an AC adapter, I am assuming I need an additional adapter to convert AC to DC. So bascially, I can run this thing off a battery (which is what I want)?

    What does the AC out/in for? It is connected to COM and NO.
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    They may be thinking of using it to control the heater and/or air conditioner. Modern units also use low voltage AC, though it won't matter from your units point of view, a relay doesn't care if the voltage is lower.
     
  11. hgmjr

    Moderator

    Jan 28, 2005
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    External links are permitted when they contribute directly to the thread's subject and when they are not peppered with commercial ads.

    hgmjr
     
  12. zenite

    Thread Starter New Member

    Dec 21, 2009
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    Thanks. So the AC IN/OUT is to be connected to the power supply for the air conditioning. Can it be used for DC too? My DIY cooler is powered by either DC or AC, so I need the thermostat to regulate both AC and DC (not at the same time). Do I need to mod the board to include DC too?
     
  13. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    You mentioned a Peliter, how big a surface are you trying to heat / cool?
     
  14. zenite

    Thread Starter New Member

    Dec 21, 2009
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    The cooler will have a volume of around 30cm x 20cm x 20cm (H).
     
  15. zenite

    Thread Starter New Member

    Dec 21, 2009
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    Does this thermostat reduce the current when the temperature is reached or does it increase the resistance? I am looking to save power with the thermostat, so if it doesn't reduce the current drawn and instead uses resistors to dissipate the excess power, then thats not what I want.
     
  16. VoodooMojo

    Active Member

    Nov 28, 2009
    503
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    the circuit board points out 12 volts + and -

    the thermostat will shut the unit off when desired temp is reached and back on after deviation.
     
    Last edited: Jan 1, 2010
  17. VoodooMojo

    Active Member

    Nov 28, 2009
    503
    53
    here you are, cost the same as your kit, has a display, is programmable and will be just as much of a project for you to hook up a power supply and relay.


    [​IMG]


    Honeywell Basic Programmable Thermostat
    Model # RTH221B Internet/Catalog # 100633100
    Store SKU # 885848
    $19.98/EA-Each




    Quantity:

    Check Your Local Store Add to My List
    This item cannot be shipped to the following state(s): HI,AK

    this is from the home depot
     
  18. zenite

    Thread Starter New Member

    Dec 21, 2009
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    Thanks. I will be looking into the Honeywell one too.
     
  19. Duane P Wetick

    Active Member

    Apr 23, 2009
    408
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    A good analogy to consider is the way a shower valve works. This is the essence of a PID control; Proportional, Integral and Derivative, and is the best way to control any process, in this case, water temperature. This should be the basis for your design.
    See www.expertune.com for a good tutorial on the subject.

    Regards, DPW [ Everyone's knowledge is in-complete...Albert Einstein]
     
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