General questions about capacitor

Hi all,

I don't have any specific circuit in quesion, just a simple beginner question about capactiors for example a super capacitor of .2F and 3 Volts. Let's say I have some tiny alternator circuit and it charges the cap and via a switch led lights up when needed. Now, in case I keep charging it and never use the stored capacitence to light up LED. What happens to the capacitor? Is it okay for the capacitor remains charged as a battery and turn on LED when needed via switch? Or capacitor can get over charged or it can pop after a day of of storage and no discharge?

 

Thanks

There are two possibilities: If the output the alternator is a regulated voltage, then once the super cap is charged to the same voltage as the alternator, then no additional current will flow into the super cap and it can exist in this equilibrium without damage.

If the alternator is not voltage regulated, when the current being delivered to the capacitor starts to go down, the voltage generated by the alternator starts to rise and subjects the super cap to voltages over 3V which will damage the capacitor.

Thanks Dean! Does this behavior apply to only super capacitors or also to electrolytic, ceramic and tantalum caps? Thanks again!

The failure modes and safety margins over the rated voltages vary, but it applies to all capacitor types.

Tantalum caps also have a pulsed current failure mode that is independent of voltage.