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Heating Jacket controlled by Arduino for Winter

Discussion in 'Microcontrollers, Programming and IoT' started by cmore082, Jul 6, 2016.

  1. cmore082

    cmore082

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    Jul 5, 2016
    Hi, I am working on a school project. I am looking towards building a heating jacket for winter (it gets really cold in Ottawa, Canada). I am doing this for my electronics class. Currently I am looking on having 3 heating elements that have roughly a maximum load of 10 V and 2 A each. I would like to use a dc-dc buck booster as a voltage regulator/voltage booster. It would impress my professor if I am able to digitally control the voltage with a micro controller. This is where I am struggling the most. I am hoping to digitally control a buck booster in order to change temperature.

    Thank you
     
  2. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Hello
    Have a look at digital potentiometers. You should be able to use one to control the feedback voltage of your buck boost.
    Thanks
    Adam
     
    cmore082 likes this.
  3. cmore082

    cmore082

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    Jul 5, 2016
    Hi Arouse1973,

    Thank you for helping. Initially I was testing it with digital potentiometers, but I am limited to the voltage across terminal A and terminal B of the digital potentiometer. For example, I tried connecting a power source of 19 V to a buck converter. I used the digital potentiometer mcp41100 to control the buck converter. I was limited to an output voltage of roughly 6 V. Would I have to buy a potentiometer with higher terminal A and B limit?
     
  4. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    What buck boost are you using? What minimum output voltage do you need?
    Thanks
    Adam
     
    cmore082 likes this.
  5. cmore082

    cmore082

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    Jul 5, 2016
    Hi Adam,

    Thanks a lot for the useful input. You are awesome and of great help!

    I took new measurements of each heating element. Each heating element (12 mm length 1.5 mm wide) at its max load of 3V and 1.5A generates 60 celsius. Say I want to have three of these heating elements on the chest (Circuit 1), three on the back (Circuit 2), and two on the stomach area (Circuit 3). I am wondering what is the best set up for the design. Looking at one circuit individually, say circuit 1, would it be best to connect the heating elements in series or in parallel?

    Once we find what is the best set up for each circuit, how should we connect all circuits (parallel or series)?

    It would be awesome to have a portable battery source that can supply power to the jacket. That's why I was wondering if I would have to use a dc booster.

    I greatly appreciate your expert advice. Thank you!
     
  6. Bluejets

    Bluejets

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    Oct 5, 2014
    Heaters do not create degrees centigrade. They do generate heat in watts which will be absorbed by the surroundings. At present with 3v and 1.5amp you will get approx. 4.5w. As a comparison, a standard bathroom heater will have 2 or maybe 4 heat lamps at 275w each.
     
    cmore082 likes this.
  7. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    If you just want to control the energy used by the heater/s then could you use PWM to control a suitable switching device like a MOSFET or BJT? Do you have a datasheet for the heating element you plan to use?

    Thanks
    Adam
     
    cmore082 likes this.
  8. Herschel Peeler

    Herschel Peeler

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    Feb 21, 2016
    I don't think a microcontroller is called for, unless you just want to use a microcontroller. Yes the PWM suggested is good. Just one area to be heated? Washable or removed before washing?
     
    cmore082 likes this.
  9. cmore082

    cmore082

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    Jul 5, 2016
    Hi Adam, I hope all is well. Unfortunately I do not have the datasheet for the heating elements. But when I tested one heating element at max capacity it was 3V 1.5A. I am going to follow your advice with using PWM and a mosfet. I would like to have 3 heating elements on the chest, another 3 in the back, and two in the stomach. I was thinking that it was best to connect each element of its region in series. Then connect all 3 circuits in parallel to a source so if a circuit fails, the others can work. If I am right, the schematic would look like the picture attached to the thread (http://imgur.com/tKsYCDq). I am thinking of controlling each circuit with a mosfet and an arduino. I also found affordable li-on batteries that have 4800mAh 3.7V

    Suppose we want to keep all 8 elements at full capacity for 3 hours, how many batteries would I need? Could you please explain why you came to that conclusion. On a final though, could we use a dc booster to booster the voltage of the batteries so we use less batteries?

    Thank a lot!
     
  10. cmore082

    cmore082

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    Jul 5, 2016
    It would be nice for it to be washable. Thank you
     
  11. BobK

    BobK

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    Jan 5, 2010
    That battery, if used perfectly efficiently, would give you 1/2 hour of running time.

    Battery: 4.8AH * 3.7V = 17.76 WH

    Heaters: 1.5 * 3 = 4.5W * 8 = 36W

    But battery AH ratings are typically done when used over 20 hours. When used over 1/2 hour it will probably produce 1/2 of that. So 15 min.

    Does this meet your expectations?

    Bob
     
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  12. BobK

    BobK

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    Jan 5, 2010
    Just for comparison, 1 liter of kerosene has 10500 WH of energy. So 2 mL of kerosene would give you more heat than your battery. Maybe you should consider a kerosene heated jacket!

    Bob
     
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  13. cmore082

    cmore082

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    Jul 5, 2016
    Hi Bob thanks for the help. I got a little bit confused when you stated that "AH ratings are typically done when used over 20 hours. When used over 1/2 hour it will probably produce 1/2 of that. So 15 min." From what I understood, if I use this battery after 20 hours of use, it will provide me 15 minutes of power for the whole circuit? I was interested in powering the whole system for approximately 3 hours. How many such batteries would I need? I am guessing a number greater than 4 batteries.....

    Would it make a difference if we use batteries together along with a dc dc booster?
    Thank you
     
  14. BobK

    BobK

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    Jan 5, 2010
    Theoretically, a battery should produce the same amount of energy whether you are drawing 1mA or 10A from it. But in real batteries that is not the case. They actually produce more energy overall when used a lower discharge rates. When a manufacturer rates the batter for 4800mAH, it is done at some current draw that makes it look good. Often this is the current draw that will make it last 20 hours, in this case 240mA. When you draw more current than that, the total energy the batter can produce drops off. If you run that same battery at 2.4A, which you would think would last 2 Hours, it will probably last more like 1 hour. That is why I divided your run time by 2, because you are drawing much more than 240mA from it.

    Bob
     
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  15. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Yes heaters in series, can't see anything wrong with that. You must also consider some safety options. Temperature feedback and maybe PWM detection cut off if the PWM stops because the heaters could potentially turn fully on. Do you not think 60 degrees is a little hot?
    Thanks
    Adam
     
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  16. Herschel Peeler

    Herschel Peeler

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    Feb 21, 2016
    Well 3 V at 1.5 Amps for three hours is what your battery will supply. You are going to need a lot of batteries. 10 elements means 10 batteries.
     
  17. cmore082

    cmore082

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    Jul 5, 2016
    Hi Bob, would you know how would the set up of the battery pack affect the performance of the circuit. For example, I understand that setting up the batteries in parallel increases current and in series increases voltage.
    Thank you

    Hi Adam, I am planning on placing temperature sensors on each element. If an element gets too hot for safety, I would have power cut off for that circuit. Not sure what you meant if cut off if PWM stops? How would that happen if I would be using a MOSFET as a switch. Maybe a malfunction in hardware or code? I don't know if having a fuse for each circuit will be good for extra safety.
    Thank you
     
  18. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    If the software had a bug and something caused it to lock up like an ESD event, there is a chance the output pin could assume a high level. Temp sensors are a great idea but they will only start to work when the temp reaches the set value. In a fault condition you want it to stop at once. A simple series capacitor can stop any D.C level activating the MOSFET as you want a changing PWM to do the control. I am just being cautious, maybe over cautious.
    Adam
     
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  19. cmore082

    cmore082

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    Jul 5, 2016
    Not at all Adam, it is important to be cautious. Thanks a lot!
     
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