Capacitors / How Long can a Capacitor Hold a charge of energy?

Question

How long can the capacitors in small electronic equipment hold a charge after the equipment is turned off? Like small Radios, mp3 players, phones for example. After you turn off a radio, how long will the capacitor hold energy?

Like say you have cellphone or an ipod for example, you turn it off and remove the battery from it. Now how long will it take until the capacitors in it are drained of any remaining charge?

Answer 1

Your asking two different questions here! A Capacitor can hold a charge indefinitely when not connected to a circuit, but the circuit itself is going to drain the power out of it. Be careful with large capacity capacitors! High voltages with a high MMF rating can be quite harmful if you handle it wrong. you can get electrocuted by the larger ones.

Answer 2

Theoretically? Or realistically? In small devices such as you're describing, capacitors will bleed off the charge within seconds, mostly due to the resistance paths in the circuitry.

Where heavy power supplies are used, such as amplifiers of a few hundred watts, it may take several minutes.

Certain high-voltage circuits, on the order of thousands of volts are designed to be exceptionally low-leaking and can conceivably hold a charge for weeks.

Back to small devices, there are now 'super' caps which hold a voltage for hours but only at very low current levels, acting more as a battery backup.

Now, with more info, for your cellphone or Ipod, you're talking a couple seconds, and there is nothing in there that's going to electrocute you anyway.

Answer 3

It depends if the maker made a discharge circuit, or if something is draining the capacitor. A charged capacitor can keep it for YEARS so be careful.. Generally do not trust that a capacitor is discharged. If you short the leads, you can be sure it is discharged

Answer 4

Usually they're designed with bleeder resistors across the bigger capacitors so they'll discharge within a few seconds. The newer variety of electrolytic capacitors have very little leakage, so they'll otherwise store charge for weeks.

So it really depends upon the circuitry. I always assume that twenty seconds ought to discharge anything.

Answer 5

I have a microwave and in order to check the capacitor--which checks good, there is no charge. and it will not charge. The diode has been replaced HV diode from capacitor to ground

Answer 6

Depends on the RC Time constant of the capacitor

http://www.tpub.com/neets/book2/3d.htm

RC TIME CONSTANT

The time required to charge a capacitor to 63 percent (actually 63.2 percent) of full charge or to discharge it to 37 percent (actually 36.8 percent) of its initial voltage is known as the TIME CONSTANT (TC) of the circuit.