Magazine article American Cinematographer

Cinema Workshop

Magazine article American Cinematographer

Cinema Workshop

Article excerpt

BATTERY MEMORY

There is no doubt that batteries are unlike most other technical devices. They do not adhere strictly to the precise "laws of operation" as most users and designers might wish. On the other hand, most battery types exhibit a "personality" that battery Engineers can plot and, thereby, remove most of the mystery and uncertainties from battery performance.

One of these "Personality Traits" is the so-called Memory effect. Despite the fact that this memory phenomenon is quite clearly defined by battery Engineers, Battery Memory has become the most misunderstood of all battery phenomena. This memory hysteria is inadvertently aggravated by several battery manufacturers who have been selling "Dememorizers" or touting cell types that allegedly do not suffer from memory. It appears that most battery users do not have a clear understanding of what memory is, where it comes from, or how it affects performance. Most ironically, the memory effect is quite rare, and even in those isolated cases where it may be present, it will have virtually no effect on the performance of a properly designed piece of equipment.

Cause:

The cause of the so-called "memory effect" can be attributed basically to two situations. The first is a precisely repetitive partial discharge. Here is the first area of misunderstanding. The key word here is precisely. This effect was first noticed in a satellite where the battery was discharged only partially to the exact same point and recharged. As the process continues, the battery will eventually "memorize" this point of partial discharge. If the battery is partially discharged to various and random depths of discharge before recharging, the memory effect is not encountered. For example, if a battery is capable of delivering one hour of service and is only called on to deliver twenty minutes on one day, forty minutes the next, ten minutes the next, etc., there will be no memory. Only when the battery is discharged to say 17 minutes one day, 18 the next, 16 the next, 17 the next, and so on will there be a memory induced. Theoretically the battery must almost be discharged by an automatic timer to be repetitively discharged with an accuracy capable of inducing the memory. …

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