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Motorola
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Abstract
The Personal Cordless Phone presents an unusual charging problem, that is, selecting the minimum charging current for the internal batteries that will maximize the battery cell life. In home use the Cord- less Phone is stored in its charging cradle at all times except when making a phone call. If the Cordless Phone is used for home and business use, it is removed from the charging cradle in the morning and not returned until the end of the day, possibly 12 to 14 hours later. In the first case little energy is removed from the battery but, in the second case the battery energy is nearly depleted. If the charge current is set for the worst case usage, the charge rate for home usage is too high. Similarly, if the rate is set for home usage, the battery will not fully charge over night.
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MOlOROLA INC. Technical Developments Volume 13 July 1991
LOW COST BATTERY CHARGER WITH VARIABLE CHARGE RATE
by John Stahl
The Personal Cordless Phone presents an unusual charging problem, that is, selecting the minimum charging current for the internal batteries that will maximize the battery cell life. In home use the Cord- less Phone is stored in its charging cradle at all times except when making a phone call. If the Cordless
Phone is used for home and business use, it is removed from the charging cradle in the morning and not returned until the end of the day, possibly 12 to 14 hours later. In the first case little energy is removed from the battery but, in the second case the battery energy is nearly depleted. If the charge current is set for the worst case usage, the charge rate for home usage is too high. Similarly, if the rate is set for home usage, the battery will not fully charge over night.
The battery cell life decreases as the charge cur- rent increases. As an example a AAA cell will yield 100% cell life when charged at a 16-20 hour rate and decreasing to 80% cell life when charged at a 5 hour rate.
The Personal Cordless Phone and the Charging Cradle are purchased as a package hence the handset
is always recharged in its "own" charger. The one-to- one correspondence between the Phone and the Charg- ing Cradle provides a simple method of adjusting the charge rate for the batteries. The Charging Cradle would contain a timer to measure the time awa...
