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Practical Application of Capacitors

  1. Jun 14, 2012 #1
    I was thinking that a car battery is a 12v source that delivers between 300 and 900 cold cranking camps. That'd put the cranking wattage at between 3600 watts and 10,800, right?

    Here's a car battery 'helper': http://goo.gl/Roo2l [Broken]

    This is hypothetical at this point but what I was wondering was since a car only pulls the 3600 to 10,800 watts for about 2 or 3 seconds, would it be possible to safely use a capacitor based system to deliver this power instead of the chemical battery?

    I know, I know, be careful.
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Jun 14, 2012 #2

    davenn

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    yes possibly, but what are you going to use to charge the capacitor ?
    the car battery ? the booster thing you linked to which appears to probably have its own battery inside it ?

    so you are going to complicate things by having some battery charge a capacitor for engine starting, instead of just starting the engine direct from the battery ?

    Dave
     
  4. Jun 14, 2012 #3
    At this point it's a theoretical exercise. Yes I agree it would be weird to have a way to charge the capacitors but not start the engine itself. You'd need a secondary generator somewhere. Which brings me to another question, how long do capacitors typically hold their charge?
     
  5. Jun 14, 2012 #4
    Sort of related.

    When a car battery dies is it the voltage that goes or the amperage or both?

    Since we are taught to hook the jumper cables up in parallel I assume it's the amperage that is lost when the battery is drained. Can you guys chime in on this?
     
  6. Jun 15, 2012 #5

    davenn

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    That would depend on the capacitor type and manufacturing. It ( a large value one) would still hold a charge after some days or so probably. It would slowly leak across the dielectric.

    Dave
     
  7. Jun 15, 2012 #6

    davenn

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    well you could say both. but principally its the voltage that goes. measure a good battery and the same type of flat battery what will you see ? .... the flat one has very little voltage

    Thats a simplified way of looking at it without going into how the battery ( whatever type) produces a voltage for a start .... google will give lots of answers there :)

    Just remember a battery doesnt store a voltage. It generates a voltage by a chemical reaction
    So when a battery is "flat" it means that the chemical reaction is no longer occurring


    cheers
    Dave
     
    Last edited: Jun 15, 2012
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