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B Boiling water w/ a car battery

  1. May 7, 2016 #1
    So... I am looking to basically convert electric energy to thermal, then mechanical energy. I am wondering how practical it would be to use a rechargeable car battery (12V, and 40Ah) to boil water into steam for a steam engine. It does not matter how long it would take, simply if it is possible/significant enough to power a steam engine (not a turbine).

  2. jcsd
  3. May 7, 2016 #2
    Here is an extremely crude (to say the least) MS Paint drawing of how all the parts are to connect.

    Attached Files:

  4. May 7, 2016 #3


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    The big question is "why?"
    Converting electrical energy directly to mechanical can be done very cheaply with up to 99% efficiency.
    I would expect a steam engine on the scale you're talking would be about 5% efficient.

    Small desktop type steam engines usually burn lamp fuel or sim. why do you want to go electric?
    With a 480 Whr battery (12V * 40Ahr), you could produce about 480 Watts of heat for an hour or 960 Watts for half an hour, or 1920 Watts for 15 mins etc etc.
    Whether this is practical depends on your goals and your definition of practical.
  5. May 8, 2016 #4


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  6. May 8, 2016 #5


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    Quite possible.
    Based on this Wilesco D2 Working Tea Candle Steam Engine video.
    Simply convert the power and energy of a tea light(32 watts & 152 watt hours, respectively) to the equivalent circuit.

    Of course, you should take adequate safety precautions when dealing with electricity and pressurized steam.
    This experiment might put your eye out, if done incorrectly.
  7. May 8, 2016 #6


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    I use a 40 watt soldering iron. The tip is immersible in water and quite capable of boiling the water. It is also intrinsically safe in that if the water boils away, the tip will not melt or destroy itself.

    A simple 60 watt inverter like the one below can drive the soldering iron from a car battery.

  8. May 8, 2016 #7
    Well, my definition of practical would look something like so:
    A very small boat capable of using a paddle wheel/prop to go at maybe 3-5 km/h.
    The only thing I want to replace is bringing solid fuels, so I'm wondering how practical it would be to use a battery instead.
  9. May 8, 2016 #8


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    You wasted our time by holding back critical information from your question. Now you're holding back more. How far must the range be in meters?

    if more than 100 meters, the battery probably not enough.
  10. May 8, 2016 #9

    Vanadium 50

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    Wouldn't it be easier to just use the battery to drive a motor to turn the wheel directly?
  11. May 9, 2016 #10


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    Have you done electric boat experiments too?

    I estimate 81 meters, based upon an electric boat test I did back in 2008.

    energy consumed: 650 watt hours
    ave speed: 5.6 kph
    dist: 2.2 km
    motor: dc electric​

    Estimated comparative efficiency of a battery powered steam driven paddle wheel vs electric: 5%
    (480wh / 650wh) * 2200 meters * 0.05 = 81 meters

    I know little about the efficiency of "practical" steam engines, so I looked it up:
    Wiki; "In practice, a steam engine exhausting the steam to atmosphere will typically have an efficiency (including the boiler) in the range of 1-10%"​

    That's where I came up with my 5% number.

  12. May 9, 2016 #11


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    That sounds about what I'd expect.
    If we consider the energy lost bringing the whole engine up to operating temp and then transmission losses to the prop I think you'd be lucky with 20 metres.
  13. May 9, 2016 #12


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    I think the OP envisions an African Queen multi day adventure without firewood.

    His picture shows a paddle wheel and no place for paddles, and no life jacket. That setup is sufficient only for a 3 meter demo trip. Even then it may capsize and send the stream engine to the bottom.

    If I wanted a romantic motorboat, I would try to find one of those glow plug engines with a single 50 cm diameter piston. Those things can run on any liquid that can burn. I saw some of those on fishing boats in Sweden. They make a marvelous sound. Whoosh wump with a period of 4 seconds. A big propeller at those ultra low speeds is remarkably efficient.

    There are also plenty of African Queen size steam boats still around, but of course they use firewood.

  14. May 9, 2016 #13
    Thank you all for your help, this gives me a good idea of the practicality of my project. The reason I'm doing electric > thermal > mechanical, instead of electric > mechanical, is because I want to build a steam engine. Simply put.
  15. May 9, 2016 #14
    Also, this is no romantic African Queen Multi-Day adventure xD. Sorry!
  16. May 9, 2016 #15


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    I actually enjoyed this thread, as I did tons of behind the seas calculations, which really drilled into my head the "energy density" of different sources.
    If you look back, you'll see that your battery has as much energy as 32 grams of gasoline, or 3 tea lights.
    At 5% efficiency, that comes out to be 1.6 grams of gas, or just 1/7 of a tea light candle.

    I used the calculations for my boat with battery electric drive, and without the steam engine interface, it would require 56 deep cycle marine batteries, for my 12 mile round trip.
    This is equivalent to 18 extra OmCheetos in my boat, which I can assure you, would not fit.

    Personally, I don't like the idea of a homemade steam engine that uses any kind of liquid fuel. I would go with wood. It has a nice energy density, and is prone not to spill everywhere, get all over you, and burn you to death, while you're trying to have fun.

    But do keep us informed, if and when you do make one. I always enjoy new "data".
    An acquaintance of mine has an electric boat, and I pester him once in a great while for how his performance statistics.
    He recently switched from "lead" to "lithium". He seemed very happy about the change.

    Unfortunately, I did not take notes the last time I ran into him.
  17. May 11, 2016 #16


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    The energy density of various fuels for comparison:

    Wood: 16.2 MJ/kg
    Methylated spirits: 30 MJ/kg
    LPG: 46 MJ/kg
    Lead acid battery: 0.17 MJ/kg

    So it would be very much harder to carry the same amount of energy in the form of a car battery than in the form of wood or methylated spirit (however this ignores possible differences in the efficiency with which that energy is turned into mechanical energy). This is the main reason we aren't all driving electric cars yet.

    Perhaps look at converting the burner to Methylated spirit or LPG if you don't want to use wood?
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