# What does a capacitor capacity really mean?

I am very new to electronics, and I am trying to use a capacitor to make my LED's stay on a little longer after I turn it off. I know that the voltage on the capacitor is the maximum limit of voltage it can take, and the fared unit of the capacitor is the capacitance, but that wasn't really clear to me, so I made a list of some stuff that I need to know to complete my goal.

1. Does a higher capacitance affect the time the charge is held?

2. If I had 5 100uf capacitors, and I connected them in parallel (which will give me 500uf), will it perform the same way as a 500uf capacitor (that was not combined with others)?

3. Does different types of capacitors hold charges longer than others?

Thank you all for feedback, help, and tips :)

• It is best to look at the maths and see what that means in practice. As you draw current from the capacitor, the voltage across it decreases. The larger the capacitances the slower the decrease in voltage. 5 capacitors in parallel gives exactly the same capacitance as one of 5 times the value. – user1582568 Jan 12 '16 at 1:50

Does a higher capacitance effect the time the charge is held?

A higher capacitance can store more charge ($Q = CV$), which can then supply a current for a longer period (assuming a constant load).

If I had 5 100uf capacitors, and I connected them in parallel(which will give me 500uf), will it perform the same way as a 500uf capacitor(that was not combined with others)?

Yes.

Does different types of capacitors hold charges longer than others?

A 1uF ceramic cap and a 1uF electrolytic cap are both 1uF, and therefore hold the same amount of charge. However, certain types of capacitors have different characteristics (ceramic caps cannot really be used to make large caps, for instance).

If you want to know how long a capacitor which is not connected to anything will hold its charge, that is dependent on the leakage current of the capacitor, which in turn is highly dependent on capacitor type and construction.

• I was looking through some articles, and a lot of videos, and I never have gotten a straight forward, and clear answer as this one, now I know what to do for this project, thank you so much :D – 3hornthrasher Jan 12 '16 at 2:14
• +1 for mentioning leakage current, which is mainly a characteristic of electrolytic capacitors. If a ceramic cap of the same size is available it will probably hold a charge longer. – Brian Drummond Jan 12 '16 at 10:59

The "Capacitance" boils down to how much charge a capacitor holds at a particular voltage.

If you compare a 100uF capacitor and a 500uF capacitor (by the way, that is huge) at a certain voltage, say 10V, the 500uF capacitor will contain 5x the number of electrons.

The equation that relates charge, voltage, and capacitance is $$Q = C \times V$$

• The example made it really easy to comprehend, thank you! – 3hornthrasher Jan 12 '16 at 2:19
• related: current is charge per unit time, i.e. I = dQ/dt. Or alternatively, Q = I * t. So if you are discharging at a constant rate, a 500uF capacitor will produce the same current for 5x longer as a 100uF capacitor. Don't forget however that as you withdraw charge, the voltage will fall accordingly! – William Brodie-Tyrrell Jan 12 '16 at 3:17
• I don't think a 500uF capacitor is huge - Electrolytics are easily available up to 10000uF; super-capacitors up to several Farads! – Icy Jan 12 '16 at 9:07
• @Icy I mean, that stuff tends to be pretty special-use. Not something you commonly design with! – Daniel Jan 12 '16 at 17:11

For easy understanding of capacitance of capacitor, think of similar notions that use a similar word.

• The capacity of a milk carton is the volume of milk it can store

• The heat capacity of an object is amount of energy an object can store per unit of temperature difference

"IN SIMILAR MANNER"

• The capacitance of the capacitor is the amount of charge that it can store per unit of potential difference.