Memory effect
As memory effect of the loss of capacity is called, which occurs at very frequent partial discharge of a nickel -cadmium batteries with sintered electrodes and other types of battery. The battery seems to remember the energy needs and to provide the time, instead of the original, only the amount of energy required in the previous unloading available. Electric manifests itself in the effect of an early voltage drop. This means a reduction in the useful capacity of the battery, since consumers require a minimum voltage. The cell voltage drops below this minimum requirement from, the cell is unsuitable for use, even though they still continue to supply electrical energy.
Cause of the memory effect
The memory effect was first described in the 1960s by NASA. Sintered NiCd batteries in satellites were charged regardless of the degree of discharge on a regular basis, ie at each orbit around the sun through solar cells. Over time, the batteries fit in the charging rhythm; their capacity was only enough until the next charging cycle, although it was significantly larger in size.
The memory effect is most likely due to two processes.
Studies of the memory effect in modern batteries
The Centre for Solar Energy and Hydrogen Research Baden- Württemberg ( STW ) examined 2001 standard NiCd, NiMH and lithium -ion batteries on their behavior in case of multiple partial discharge. In this case, a decrease in the cell voltage after repeated partial discharge (ten Teilentlade charging cycles and more) has been determined, which, however, was always less than 0.05 volts. Previously published reduction of the cell voltage more than 0.1 volts was observed. The reduction of the cell voltage could be reversed by single discharge at normal discharge voltage and recharge. Amazingly, NiCd and NiMH batteries behaved very similar, but it is called the NiMH battery from the battery inertia effect. Li batteries have this effect only in small sizes. It can be concluded that for this effect, none of the above causes of the question, at which cadmium is always involved.
The authors of the study conclude that it is the battery manufacturers have succeeded through material selection or changes in technology, largely eliminate the memory effect, and come to the following recommendations:
- A complete discharge before each charge is not necessary.
- Random unloading, after about 50 Teilentladezyklen is recommended.
The battery life may rather be significantly increased by partial discharges - this applies to NiMH, and lithium batteries. In hybrid cars more than ten times as much part - loading cycles are possible, as if they would discharge 100%. The throughput can be, for example, tripled in pedelec batteries, which would more than double the life span.