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# How to charge a capacitor? Answered

I read some where that you need a rising amount of volts to charge a capacitor, but I also always see around that you can just charge a capacitor on just a straight battery that is DC. I am very confused how you can and should charge a capacitor.

I think the formula for charging a capacitor is i=C(dV/dT)

Thanks

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## Discussions

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basically, a capacitor, in short circuit with a battery, will act like a battery. It will 'charge' up to whatever voltage the battery is willing to put out. The internal 'resistance' of the capacitor will become evident as it charges. As the plates get their charge, they start to oppose the incoming charge. When the internal voltage of the capacitor reaches the same voltage as its source, it will have infinite resistance (in a charging sense), and no more current will flow. The difference between a battery and a capacitor (of similar voltage ratings and physical size) is that the capacitor holds 'less' energy (in all but a few cases) - but that capacitor can dump its entire charge in a few nanoseconds, where the battery couldn't possibly dump that much charge. Tortise and the hair analogy I guess... Long story short: Hook it up to dc current, and it will charge until full, then stop charging. If you don't go over the voltage rating of the capacitor, you wont harm it by 'leaving it charged' because it stops taking energy when its full.

Note too that in many (most?) real-world applications you don't "charge" a capacitor -- you just let it charge and discharge as signal is applied to it.

orksecurity, you are referring to when a capacitor is used to filter a signal, often on the output of a switched mode power supply or voltage regulator of any sort. In that sense, the capacitor is taking on extra charge that is above the average output, and outputting charge when the output signal is below the average output. This allows for a smooth, DC output in most situations.

However, this thread is talking about using capacitors as energy storage elements to be later discharged in a very violent and entertaining manner.

i also have a question....im very new to electronics but cant you just hook it up to maybe a wallwort or a ac to dc transformer?

Yeahh .. I too have a Question ....
whenever i connect a 9 volt battery to a capacitor (in parallel with a digital multimeter) .. and in series with a resistor .... It charges up to 9 volts .. but as i take out the battery and connect the two wires .. it directly goes to 0.01-0.05 in less than a second ...
why is that ? is this because the capacitor releases it charge in nanoseconds ?