How long can capacitors store energy

The capacitor - an energy storage device



Numberdescriptiondata sheet
1 Battery / voltage source 9V 
1Resistance 470 ohms 
2Electrolytic capacitor 100 µF / 16V 
1Electrolytic capacitor 470 µF / 16V 
2Micro switch
1Standard light emitting diode 3mm or 5mm 3mm, 5mm




Who does not know them, the automatic staircase lighting, the electronic egg timers, the flashing lights etc .. They all have something in common. You need a time-defining component. Among other things, capacitors can be used for this. These have the ability to store electricity and slowly release it again. So they work in a similar way to batteries that everyone probably knows. Only capacitors work with considerably less 'storage power'.


Some capacitors


There are 2 large groups. These are the polarized and non-polarized capacitor types. With the polarized types you have to pay attention to the polarity, similar to a battery, and the unpolarized types can be connected as desired. Why some types are polarized and others are not polarized depends on the structure of the capacitor.


The simplest capacitor consists of 2 metal foils that are on top of each other. Both separated by an insulating layer, also called the dielectric. A voltage can now be applied to the metal foils. Due to the desire of the electrons to rebalance themselves, they remain present on the plates, that is, electricity is stored until a charge compensation is made possible with the help of a consumer.


How much electricity a capacitor can store is precisely defined. This is given in Farad (F). 1 Farad is reached when the capacitor can deliver a current of 1 A for 1 second at 1 V. In practice, however, capacities that are a millionth of 1 F are used. E.g. 100 µF. That means 100 millionths of a farad.



Charging and discharging a capacitor



To charge a capacitor now, you just have to apply a voltage to it. With larger capacities you should use a charging resistor, otherwise the capacitor could be damaged by the very high current that can arise.

If the circuit is put into operation, the button S1 must first be pressed. This enables the condenser to 'soak up' with electricity. If this is to be returned, just press button S2. The connected LED flashes briefly, but then quickly becomes darker. The stored energy was then released again via the light-emitting diode.

If the capacitor is now replaced by a larger one, the discharge time also increases. That means the LED lights up longer. If the capacitor is exchanged for one with a larger capacity, e.g. 470µF, and if the experiment is repeated, you will quickly notice that the LED lights up considerably longer. 4.7x as long with a 470µF capacitor.

Incidentally, an electrolytic capacitor is used in this circuit, which enables quite large capacities. With this type, however, attention must be paid to the polarity. However, this is printed on the component.



Series and parallel connection of the capacitor



It happens again and again that the capacity of a capacitor is insufficient. There are 2 options:

1. Take a corresponding larger capacitor or

2. Two capacitors are simply connected in parallel. This increases the disk size and, accordingly, the capacity. If you repeat the last attempt with 2 capacitors, you will quickly find that the light-emitting diode has doubled its light duration.

But what happens when connected in series?



Anyone who expected the capacity to be halved here will not be disappointed. The LED only stays in operation half the time as if only the 100 µF had been there alone. Strictly speaking, this doubles the strength of the dielectric.

When capacitors are connected in series and in parallel, it is exactly the opposite of that with resistors.