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IP.com Disclosure Number: IPCOM000007051D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2002-Feb-21

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Scott M. Garrett


Code resistors are used in batteries to allow a charger to adjust the current output so that the same "c" rate can be applied to different capacity batter- ies (i.e. a 550 mAH battery is charged at 550 mA while a 1500 mAH battery is charged at 1.5 A). By doing this, different capacity batteries will be recharged in approximately the same time, and their useful service life is maximized. Presently, code resis- tors have their own dedicated electrical contact for both the battery and the charger. These contacts not only represent an increase in cost but also an addi- tional opportunity for product failure in both bat- tery and charger. Furthermore, the only time the code resistor is used on most batteries is at the begin- ning of the charge process, before current is applied to the battery. Which means that 99% of the time, the code resistor does nothing. Therefore it would be advantageous to eliminate the code resistor con- tact while retaining the ability to determine the cor- rect charger current when a battery is inserted into a charger. This brief article describes a method to accomplish both.