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| electric batteries | |
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__NOTOC__ ORIGINAL MEANING 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 Satellite s (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 A much more common process often ascribed to memory effect is voltage depression. 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 Camera s. 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 Charger s typically overcharge. Urban Legend s about the memory effect, universally referring to voltage depression, have led to all sorts of superstitious 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 pack, correcting the problem in the short term but eventually leading to a considerably shorter battery life. To perform this properly, each cell must be individually discharged, not the entire pack as a whole. Otherwise, some cells discharge before others, causing them to be charged in reverse by the remaining cells, severely damaging them. LCD MEMORY EFFECT Passive Matrix Addressing takes advantage of Hysteresis to display images on Liquid Crystal Display s. Without this effect, passive matrix LCD panels would not be able to display anything. Although similar in name, this effect is completely different from the battery memory effect". Similarly; Active-matrix LCD s whose pixels use dedicated transistors are sometimes "dead pixels". EXTERNAL LINKS |
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