Battery Conservation

Discussion in 'The Projects Forum' started by BobH10, Aug 31, 2011.

  1. BobH10

    Thread Starter New Member

    Aug 31, 2011
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    Hello, I'm just an amateur dabbling in electronics, and I thought I would try to go online to see if I could get some help on my project.

    I'm trying to think of a way to build a portable battery operated chocolate melter. Basically what I have is a heating element attached to a battery, and it works good enough except that it drains the battery too quickly.

    To solve this problem of battery drain I'm thinking of incorporating some type of current limiting circuit/diode to limit the current going to the element. Then adjust the resistance in the heating element so that it requires less current to reach the desired temperature. This way the battery would not be "freewheeling" all its current through element, and could potentially save battery life.

    Does this make sense? Going in the right direction? I want to keep this very simple, so would it be as easy as soldering in a current limiting zener diode between the battery and the element, or is an adjustable regulator like the LM317 from national semi needed?

    Thank you in advance for any help:)
     
  2. saturation

    Member

    Dec 21, 2008
    22
    4
    You can do it, but not sure its practical. Based on being portable as a requirement, the amount of energy needed to melt cocoa butter to 100F, you'll run through AA batteries too quickly. So you'll need Li batteries, and thus now you need a charging circuit, as primary Li cells won't last long either. This is like making a hand warmer using batteries, they don't do very well, most folks use chemical or gas power, to get this amount of BTU in a small form. You are better off buying a small hand held blow torch. Note, this regardless of whether you use a wire, ceramic, or IR heating element, all will consume the power needed to generate the watts needed to melt your material ... note a lot of this energy will be used heating the plate or pan you use, and if not, once by say direct heat the chocolate will solidfy if the pan its on is also not 100F.

    [​IMG]

    The above at Amazon is $10. You can find them retail at Home Depot and such.
     
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  3. #12

    Expert

    Nov 30, 2010
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    You're running up against a law of thermodynamics. For instance, a B.T.U (British Thermal Unit) will heat one pound of water by one degree F if all the energy goes into the water quickly (so the water doesn't cool off just from sitting around for some time). A watt hour causes 3.413 B.T.U.s of heat.

    Whatever amount of BTUs you need to raise the temperature of how many pounds of chocolate by "this many" degrees is not negotiable. Slowing down the process by wasting energy in regulators, resistors, or such as that, will not decrease how much energy you will need.

    "requires less current to reach the desired temperature" in the way you used that phrase, is simply a mistake. The only way to use less current to reach the desired temperature is to use more volts. That is because watts = volts times amps. If you use half as much current (amps) you will need twice as much voltage to get the same amount of energy. The way this is accomplished is to increase the resistance of the heater, but that is usually inconvenient because it means throwing out your heating element and getting a different one.

    Feel free to ask more questions if you need clarification.
     
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  4. wayneh

    Expert

    Sep 9, 2010
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    The only way this isn't a limiting truth is if your element is getting so hot that heat leaves the system - the chocolate - without doing the job of melting chocolate. For instance if it's really hot and frying a small region or radiating heat that the bulk of the chocolate isn't seeing.

    If you don't have any of those issues, your problem is simple physics. Batteries just don't contain enough power to warm up large masses of ... anything.

    One of those things you use for aches and pains might be a good option for you. They use a supersaturated solution of some salt - magnesium sulfate? can't recall - and a clicker thing to initiate a phase a change. A LOT of heat is then released at the melting point. So it's very simple with no electronics or moving parts but it gives you reliable temperature control at "hot" to the touch range. And they're easily restored by cooking the spent (crystallized) bag to turn it back to liquid.
     
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  5. BobH10

    Thread Starter New Member

    Aug 31, 2011
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    Thank you all for the input:). The amount of chocolate that will actually be melted at one time is small, so I'm still hopeful that a battery system will work. I'm changing the design to incorporate Li-ion batteries, and increasing the volts as suggested.

    I'll try to incorporate an auto shutoff and momentary on/off feature using a 555 timer and a CD4023B CMOS NAND Gate. A want to avoid incorporating a charging circuit (afraid of cost/size limitations), so I'm looking at the 14500 batteries sized AA, which could be removed from the unit and recharged in separate charger.

    I have an initial schematic drawn on paper, but I'm still working on it. I am now concerned that if the current initially flows though the CMOS NAND Gate/555 timer circuit (auto shutoff), that the output current be not be sufficient for the heating element:confused:. But again, I'm learning and having fun so maybe I just order some parts and put it on a breadboard and see what happens;).
     
  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,771
    930
    [​IMG]
    is one simple idea that would allow some amount of power control. Just replace M1 with your heating element

    Lots of good ideas here: http://www.elektrotekno.com/about49160.html

    Most of those circuits that drive a motor will do just as well with a resistive heating element.
     
  7. wayneh

    Expert

    Sep 9, 2010
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    I wonder if a small TEC (peltier) would make a good heater for this application. A portion, maybe 10% of the heat it delivers is moved from the cold side - the room - to the hot side - the chocolate, like using a heat pump. It might give a bit more efficiency than a purely resistive heater.
     
  8. BobH10

    Thread Starter New Member

    Aug 31, 2011
    4
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    Great web site and thanks for the ideas.:D


    Never heard of TEC, I'll have to research this.:)
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    TECs are very power-hungry.

    Heating elements (like resistive wire) are actually very good at converting electrical power to heat; better than 99%.

    It's likely that your biggest difficulty will be keeping the heat where it's needed, instead of allowing it to be radiated or conducted away from your target (the chocolate).
     
  10. wayneh

    Expert

    Sep 9, 2010
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    For cooling yes, but they're maybe 110% efficient at making heat, since they can move heat from the cold side to the hot side.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    Blasphemy!
    You can't even get to 100% efficiency - although you can get close.

    Exceeding 100% efficiency implies over-unity, which is of course impossible.

    If it were possible, I'd have a vehicle that would convert smog to gasoline while I was driving it home to work. ;)
     
  12. Smoke_Maker

    Active Member

    Sep 24, 2007
    126
    15
    What about using one of the 12 volt coffee warmers and increase voltage to the correct temp, turning off the current at the correct temp sounds like a job for a thermostatic switch.

    The less circuitry you the more energy you will save, heating element, battery, and a switch is all you need.
     
  13. wayneh

    Expert

    Sep 9, 2010
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    Hah, well of course it's not more than 100% in a thermodynamic sense, only in the sense of the energy that gets paid for, the electricity. But really, the heat that arrives at the hot side is the sum of the electrical power consumed plus whatever heat gets moved from the cold side.

    When cooling, that's why a TEC is so poor; it only moves about 10% as much as it consumes. All that consumed heat shows up on the hot side - in addition to whatever heat was removed from the cooled area - and must be removed to achieve any cooling. A normal air conditioner gives more like a 10:1 ratio of heat moved to heat consumed.

    So the ideal solution to melting chocolate would be a tiny heat pump that could put 10 calories of heat into the chocolate for every one calorie consumed from the battery, cooling the room by 9 calories. Unfortunately there is no such tiny machine yet.
     
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