Difference between capacitor and battery

Discussion in 'General Electronics Chat' started by saim4, Aug 25, 2016.

  1. saim4

    Thread Starter New Member

    Aug 2, 2016
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    Hi, anyone tell me difference between capacitor and battery. I am pretty confused with them as both charge/discharge and outputs current.Can't be they used interchangeably?
     
  2. Robin66

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    Jan 5, 2016
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    A capacitor stores charge in a raw form and it's quick and efficient to move about. A battery actually converts chemical energy to electrical energy which is a slower and less efficient process but allows much higher storage density ie. charge per kg or per m^3.
     
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  3. DGElder

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  4. OBW0549

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    You might think so; but in reality capacitors simply can't compete with batteries in terms of charge storage capacity per weight, size or cost. For example, to replace an ordinary little 18650-type lithium ion battery (a bit bigger than an AA cell) costing $5 and storing 3000 mAH of charge, would require several thousand dollars worth of supercapacitors and would occupy somewhere around a cubic foot of space.

    No contest.
     
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  5. wayneh

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    In addition to what @OBW0549 noted, another crucial distinction between batteries and capacitors is that a capacitor voltage drops continuously during discharge while a battery maintains a nearly constant voltage until it's fully discharged. A battery provides energy at a (nearly) regulated voltage with no extra components. This is because it's converting chemical energy into electrical, and the thermodynamics of that change only a little during discharge. This helps during recharge as well.
     
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  6. saim4

    Thread Starter New Member

    Aug 2, 2016
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    Thanks everybody a lot.Now I can move on to some other devices rather being stuck in capacitor.
     
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  7. BR-549

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    Sep 22, 2013
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    Both store charge, but in a different state. In a cap, accumulated free charge has a gaseous character.
    In a battery, the charge is in a liquid/solution potential state. More charge density.
     
  8. ian field

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    Oct 27, 2012
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    A capacitor is simply 2 plates separated by a dielectric - the charge on one plate or the other is pretty much an abundance of electrons.

    Batteries store energy that is released by the progress of a chemical reaction - some batteries are even more different to capacitors by not being rechargeable.
     
  9. nsaspook

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    Aug 27, 2009
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    Sorry to be pedantic (Yeah, and pulleys store rope!) but neither stores charge in an electronics or physics sense as the total amount of charge in the battery/electronics capacitor (not a physics-classroom capacitor of spheres) remains the same. Charge is separated between plates in both cases (mobile ions or electrons) resulting in an electric field (voltage). A current results when those mobile charges move around that combined with the voltage results in electrical energy transport.

    Charge and energy are two different things.
     
    Last edited: Aug 25, 2016
  10. Robin66

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    Jan 5, 2016
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    You can replace "charge" with "charge differential" if you like, but bearing in mind the basic lack of understanding in the OP do you think that level of pedantry is appropriate?
     
  11. nsaspook

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    Yes, because it's a very important distinction on what's the true difference that was mainly directed at one poster and the OP. There is the colloquial usage of 'charge' that's commonly used when we store energy and the electronics/physics meaning of charge that's a property of matter and can be used in different types of systems to store energy.
     
  12. wayneh

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    I understand and agree with the pedantry, but there are also semantics to deal with. If you can both charge and discharge a capacitor, is it really wrong to say it holds a charge? "Charge" can be just shorthand for energy as electric field due to charge separation, instead of the incorrect notion of a net charge.
     
  13. shteii01

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    cap, fast.
    bat, slow.
     
  14. nsaspook

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    I agree it's messy and imprecise because of the nature of the archaic term 'charge'.
    You can charge and discharge a rifle but you generally don't say a modern rifle stores or holds a physical charge today. The rifle holds cartridges (an energy storage system) that uses a power 'charge' to push a bullet down the barrel.

    I don't have much of a problem with holds a charge, it's stores that tickled my fancy.
     
    Last edited: Aug 25, 2016
  15. Tonyr1084

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    Sep 24, 2015
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    While the semantics of it may represent the most basic form and description of what goes on in a capacitor, the physics of it is not that at all. The dielectric between two plates is made up of atoms, consisting of protons and electrons. Likely neutrons as well, but they carry no charge (so to say).

    In a capacitor, when a voltage is present on one plate and the other plate is the opposite - be it ground or a negative voltage or something, lets not get caught up in that argument - but when a voltage is present on one plate it stretches and elongates the orbit of the electrons that orbit the protons. They're held in that state because there is nothing to counteract that effect. Hence, when you short the leads of the capacitor you provide a path for free electrons to move along in order to relieve the stress the stretched orbiting electrons are trapped in. In other words, when the electrons are allowed to return to their natural state they give off an energy - an electricity - a current. If you charge one plate positive then the orbits (lets say for sake of speak) the orbits are pulled to the left. If you charge that same plate with a negative charge the orbits are pulled to the right.

    Depending on the dielectric makeup, the capacitor will have differing characteristics. The thickness of the dielectric may dictate voltage capability of the capacitor. It also affects the capacitance. Also affecting the capacitance is the amount of plate area. More plate area means more capacitance as well.

    But the dielectric is actually an insulator. That's why DC does not pass through a capacitor. Honestly, AC doesn't either, but those orbiting electrons make it seem like it does. Because they can take on a charge and deliver it back at a given rate AC of a specific frequency can pass through almost unimpeded.

    Ever notice on speakers with tweeters - how they have a capacitor in series with the speaker? Low frequencies can't pass through the capacitor because the action is too slow. The more the capacitor charges the greater its resistance. Hence, low frequencies are blocked from reaching the tweeter while the higher frequencies can fly right through the cap. (even though electrons don't really pass through the cap)

    Batteries are chemical while capacitors are atomic in nature (the nucleus of the atom and its orbiting electrons)

    OK somebody blast me for my post. I'm ready.
     
  16. GopherT

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    Capacitor = physics
    Battery = chemistry
     
  17. Tonyr1084

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    Sep 24, 2015
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    Currently I have two dash cameras. Both are powered from the cars electrical system. However each has a "battery" in it. One battery is a Lithium Ion battery and the other is a super capacitor. (not really a battery at all)

    The battery backed up camera can operate for tens of minutes on a single charge while the super capacitor unit can luckily operate for up to 3 minutes on a single charge.

    The advantage of the super capacitor is that it's not as susceptible to the heat of the car in the sunlight all day long as the battery is. Hence, the super capacitor should last longer (in terms of years, not in minutes of charge). The battery powered camera has the advantage of being able to sense G shock (someone hitting the car in a parking lot) and start recording for a few minutes (depending on how long I set it for (2, 3 or 5 minutes)). The super cap? No such hope for being able to sit and monitor G shock or start recording when an impact has been detected.

    [additional]

    A capacitor can deliver 100% of its charge in nearly an instant of time whereas a battery can not.

    Go to a drug store and ask if you can have a disposable camera that someone has brought in for processing. Get one with a flash unit. You'll take that thing home and dismantle it. You'll get a pretty good AA battery out of it, but the circuit is what's worth playing with ( C A R E F U L L Y ! ). You can charge the circuit by pressing the charge cycle button. The flash capacitor will charge up to somewhere around 300 volts DC (keep in mind I said C A R E F U L L Y ! ). Take a piece of wire and short it across the capacitor. You'll probably jump when you hear and see the spark - yes, 100% of its stored energy delivered in a virtual instant. If you were to short the battery in the same way you wouldn't get anywhere near the show you got with the capacitor. And after you've shorted the capacitor it's completely discharged. If you short the battery for a second, the battery is still holding a significant charge (depending on how long you short it and how depleted it was when you got it).

    Capacitors and batteries are alike in that they hold and deliver a charge. Beyond that there is NOTHING similar about them.
     
    Last edited: Aug 26, 2016
  18. nsaspook

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    [​IMG]
     
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  19. nsaspook

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    Remember, the dielectric between the plates in a capacitor can be a vacuum.
     
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  20. Tonyr1084

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    Sep 24, 2015
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    Absolutely they can be. In fact, I've played with variable capacitors that were "Air Core" caps. Radio tuners. Tube type radios had these tuning caps long before PLL (Phase Lock Loop) tuners.

    I know nothing about caps that operate in a vacuum with nothing between them. I'd imagine that anything less than a perfect vacuum would still have air molecules between the plates. Just how much air - I couldn't know. Nor would I know how changes in the air volume would affect the cap.

    Exotic parts aside, the basic cap you find on all hobbyist work benches are not going to be vacuum sealed caps. But your point is valid.
     
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