Memory effect
|
|
With batteries, the memory effect, also known as lazy battery effect, is an effect observed in some rechargeable batteries that causes them to hold less charge. The term has become almost universal in describing any such effect, though in fact it describes one very specific case.
Memory effect occurs when a sintered-plate nickel-cadmium (NiCd) battery is repeatedly discharged to a particular level above a full discharge, that is, only "partially used", and then recharged to an equally precise "full" level. This "real" memory effect is extremely rare and is found only on very expensive, rare, and older unattended electronics such as communications satellites (which repeatedly use exactly the same amount of power while in the Earth's shadow). Repeated attempts to duplicate it in the lab have proven difficult.
Voltage depression is a much more common effect which is often ascribed to memory effect. In this case the peak voltage of the battery drops more quickly than normal as it is used, even though the total power remains almost the same. In modern electronics equipment that monitors the voltage to indicate battery charge, the battery appears to be draining very quickly and therefore about to run out of power. To the user it appears the battery is not holding its full charge, which seems similar to memory effect. This is a common problem with high-load devices such as digital cameras.
Voltage depression is caused by repeated over-charging of a battery, which causes the formation of small crystals of electrolyte on the plates. These can clog the plates, increasing resistance and lowering the voltage of some individual cells in the battery. This results in a seemingly rapid discharge as those individual cells discharge quickly and the voltage of the battery as a whole suddenly falls. This effect is very common, as consumer trickle chargers typically overcharge.
Urban legends about the memory effect, universally referring to voltage depression, have led to all sorts of quasi-religious behaviour in order to "fix" dead batteries. The most common recommendation is to completely drain the battery in some other device in order to dissolve the crystals. While this works in theory, it more often leads to damage to the other cells in the battery, correcting the problem in the short term but eventually leading to a considerably shorter battery life.
LCD memory effect
Passive matrix addressing takes advantage of hysteresis to display images on a LCD. Without this effect, passive matrix LCD panels wouldn't be able to display anything. This effect is completely different from the "battery memory effect".
External links
- NiCd Batteries do NOT have "memory" (http://www.repairfaq.org/ELE/F_NiCd_Memory.html)