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Heat Generation

Discussion in 'General Electronics Discussion' started by Mywk, Mar 13, 2012.

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  1. Mywk

    Mywk

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    Mar 13, 2012
    Hey Everyone,

    I'm new here, just another person who finds electronic the best hobby possible, I have very low knowledge in what concerns to electronics, however I learn fast as hell. I'm currently taking a degree in Maths & Computer Science so I'm more of a programmer :)

    So, I've been asked for a chicken eggs incubator system, those are really really high priced (like 400~600€), and it can be done with less than 20€.

    Box, made of styrofoam, 45cm x 20cm, and about 20cm height, for the system I will use a simple PIC (bought programmer and a PIC 12C508A today so I'm just going to learn how to program in it today also) and will use it to control temperature with a LM35 sensor (if > 38C || < 35C) turn on the HEAT generator.
    For humidity I will just add a sponge with water inside but if anyone knows how to make a simple cheap humidity controller please let me know!

    The thing is, the HEAT, I was thinking about just using a 25Watts old light bulb but I'm wondering if there is any more efficient way to generate heat with less power!

    Thanks In Advance!
     
  2. poor mystic

    poor mystic

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    Apr 8, 2011
    The thing is, that heat may be considered the most degraded form of ordered energy; it's best you learn some physics - this is the study of the real world and is indispensible in engineering work.
    For now I want to say that heat is always generated with the same efficiency regardless of the device used as a transducer.
    I also suggest that a 1W resistor will probably provide plenty of heat.
     
  3. duke37

    duke37

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    Jan 9, 2011
    An old style of grain moisture meter consisted of a perforated metal tube with a horsehair filament up the centre which pulled a pointer round, depending on the moisture content of the air. It took a few minutes to stabilise.
    You could perhaps use a similar system to move a potentiometer or capacitor.
    First, find your horse.
     
  4. poor mystic

    poor mystic

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    Apr 8, 2011
    Human hair works well also; can you find a woman?
     
  5. Mywk

    Mywk

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    Mar 13, 2012
    For now it seems the only thing I've learned so far is that PIC12C508A is a dam one-time-only programmable Microcontroller so it sucks for learning, gotta replace it.

    Wait, so you are actually telling me that no matter the amount of Watts used, the generated heat will always be the same? No matter if its a 25W light bulb or a 25W fluorescent light?
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    If you want to generate heat efficiently, then you would look at a heat pump.

    However, for the small amount of heat you require, unless you're on an enormously tight energy budget (like you're sending this up to operate on a space station or inside a satellite) then a simple resistive source like your lamp or a plain old resistor will work fine.

    If you can't find a woman, you can grow your own hair too.
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    The amount of energy converted to light is pretty small in either case. The rest is converted to heat.

    If you're just wanting the heat, there's no point in getting the most efficient generator of light.

    In terms of efficiency of generating heat, common devices come out at (approximately):

    Resistor - 100%
    Filament light bulb - 98.9%
    Fluorescent - 92%
    LED - 90%
     
  8. poor mystic

    poor mystic

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    Apr 8, 2011
    Thanks Steve
    I think that 25W will cook your eggs, fairly quickly.
    So I'd use a smaller heat source which can be controlled by a lighter component.
     
  9. jackorocko

    jackorocko

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    Apr 4, 2010

    I got a horse, but I am missing how this works. What is the point of the perforated metal tube exactly? Got a link that explains this?
     
  10. duke37

    duke37

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    Jan 9, 2011
    The perforated metal tube was stuffed into the pile of grain and the perforations allowed the damp air in the grain to diffuse into the tube so equilibrating with the hair moisture content. The variation of the length of the hair relative to the tube length pulls a pointer round.

    You could use a led and photo detector with a flag inbetween.

    This was made long before computer links were thought of.

    I have had a look at instruments intended to go into home made barometers. Hygrometers are available but it would need some ingenuity to interface them with electronics
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    There are some fairly simple humidity detectors out there. I saw this one the other day.
     
  12. Mywk

    Mywk

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    Mar 13, 2012
    @Steve Thanks, I couldn't find any humidity sensor in my local electronics store!

    So, I've been learning to use the PIC's programmer, after a lot of ASM I decided to move to C and currently I have a complete AI system for 20~30 days egg-hatching, but still am trying to figure out the best way way to generate heat.

    So, simply put:
    What kind of resistor, how many of them, and what voltage for a small ventilated box to maintain the 37Cº?
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You need to determine how much heat is required.

    The amount of heat required depends on many factors, including:

    1) the amount of insulation
    2) the temperature differential between inside and outside
    3) the amount of ventilation
    4) how quickly you want to be able to effect a change in temperature.

    I would recommend setting up your incubator with a light fitting and a thermometer inside. Place some random light bulb inside (say 40W) and measure the time it takes to get up to the required temperature. Also measure the temperature outside the box. Note the temerature every (say) 5 minutes and graph it. Note the temperature at which the curve flattens off.

    Armed with this information you can estimate what the minimum external temperature could be and still maintain at least 37C inside. If this is insufficient, you need a higher wattage bulb. You can also estimate the amount of time it will take to get back to 37C from any combination of inside and outside temperatures (within reason). If this is too long, raise the wattage.

    You then need to create a controller that can either turn the lamp on and off to regulate the temperature, or to do proportional control of the bulb to keep it emitting just the right amount of heat.

    I would recommend using a light bulb because it:

    a) is a good heat source
    b) is really cheap
    c) is pretty much guaranteed not to overheat
    d) provides a handy indication when it's "on"

    You may wish to consider something else if light (or flashing light) is contraindicated (or you could dip the bulb in black paint).
     
  14. jackorocko

    jackorocko

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    Apr 4, 2010
    Maybe I am whack, but would it be possible to use PWM to pulse a large voltage to a resistor? Then you could use a temperature sensor and a pic to increase or decrease the PWM output to the resistor controlling the heat. Maybe you could do this with a light bulb? Just me thinking out loud is all.
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You certainly can. It's at the heart of a PID controller.
     
  16. poor mystic

    poor mystic

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    Apr 8, 2011
    The hair could tighten a pair of capacitive plates together, so C would increase and change the resonant frequency of a tank. Tables derived from experiment could convert from freqency to humidity.
     
  17. duke37

    duke37

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    Jan 9, 2011
    The humidity sensor as found by Steve seems the way to go but if you wish to make your own, then a flag in a slotted optical coupler would be the easiest.

    You will need to realise that the sensor, whatever it is will not respond instantly since time will be required for the moisture to diffuse through the air. Thus, the humidity should be measured at intervals and only a small amount of water added if necessary.
     
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