What is the "memory effect" of capacitors?

Question

What is the "memory effect" of capacitors?

Answer 1

Capacitors dont have a memory, however they can be used to store electrical charge in discrete amounts.

This can be used in combination with other components in electronic devices to store numbers or other data, providing memory support for calculators and other things.

Capacitors are two conducting plates separated by a dielectric that halts the conduction of charge until a certain potential difference exists over the plates, providing sufficient EMF for charge to flow through the dielectric.

Answer 2

You can see this in some types of capacitors.

After you discharge a cap fully, the cap recovers some of it's charge.

In other words, after you discharge it, and remove the short, and wait a short period, a small voltage appears on the capacitor.

This is called dielectric storage.

What happens is that some of the charge gets pushed into the dielectric, and after the cap is discharged, this charge leaks back to the plates.

This is a problem is high quality instrumentation equipment.

You can avoid it by using high quality caps with teflon or polystyrene dielectric.

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Answer 3

I don't recall to read about Capacitors memory effect (perhaps I am suffering of memory effect... )

Memory Effect is much more pronounced in Rechargeable Batteries, mostly the Nickel Cadmium (NiCD) type.

The way the battery is produced, it absorbs energy (low impedance for incoming recharging current) when the internal voltage at the plates is below certain Voltage, normally 1.2Vdc.  When during recharging the voltage reaches close to the 1.2Vdc the internal impedance grows high and the recharging current drops down to a point when the cell can not charge more energy, it may still receiving current but will convert it in heat without storing it.

In time and by chemical situations, the trigger level of increasing impedance goes down, the battery will never recharge to fully 1.2Vdc, it may "think" it is fully loaded when the internal voltage reaches some lower voltage level, such as 1.1Vdc or even lower.

By doing so, the battery will recharge a little, enough to trick the charger, but in real the battery is holding little charge, and will not charge more, no matter how long you keep it charging.

Some popular internet recommendations, say you need to fully discharge the NiCD batteries prior recharging, by doing so, the "memory effect" is reset and the battery recharges with full charge.