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Methods of controlling the application and termination of charge to a rechargeable battery
| Details |
Inventors: Falcon, Carl B.;
Assignee: Galaxy Power, Inc. A Pennsylvania Corporation (Valley Forge, PA)
Primary Examiner: Tso; Edward H.
Assistant Examiner:
Attorney, Agent or Firm: Cohen, Pontani, Lieberman, Pavane
As a substantially constant charge current is applied to a battery, the voltage is periodically measured and the slope of the voltage characteristic is calculated. The minimum slope of the bottom peak of the slope profile is dynamically identified and, as appropriate, updated and stored. With each identification and update of the minimum slope, a trigger threshold between the minimum slope and top peak is defined, and then stored, by adding a trigger value to the minimum slope. A termination threshold or value between the minimum slope and the trigger threshold may also be calculated and stored with each such identification and update of the minimum slope. When the calculated slope, increasing from the bottom peak, reaches the trigger threshold, the method is armed--as by setting a trigger threshold flag--so that when the calculated slope thereafter once again passes through the trigger threshold and then reaches the termination threshold, full-current charging of the battery is terminated. The termination threshold--which identifies the substantially fully-charged state of the battery--may, in some forms of the invention, be preset to equal the minimum slope value. Premature termination resulting from a high impedance spike or inflection point occurring in the voltage profile when charging current is initially applied to the battery may be avoided by gradually increasing the applied charging current at the beginning of the charging process. |
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is broadly directed to a method and apparatus for charging a rechargeable battery and, more particularly, to a method and apparatus for controlling the rapid and efficient charging of such a battery and then terminating the application of charge when the battery has been fully charged.
The term fully charged is intended to connote that condition of a battery in which the further application of electrical energy does not result in an appreciable increase in the amount of charge that the battery is holding.
In accordance with the invention, the appropriate charge termination point is dynamically determined by monitoring a characteristic parameter of the battery and controlling the application of charge in response to changes in that parameter so as to avoid unintended overcharging of the battery.
In a most preferred form of the invention, the monitored characteristic is the no load voltage of the battery under charge.
The invention is particularly intended for use in the charging of nickel-cadmium and/or nickel-metal hydride batteries, although its application to other battery types and chemistries exhibiting similar or equivalent or analogous parameter characteristics is also contemplated and intended.
Such batteries are typically comprised of a plurality of individual cells arranged in a serial and/or parallel relationship although, for purposes of this disclosure, the terms battery and cell are sometimes used interchangeably.
Also for convenience, rather than by way of limitation, the invention is herein described with specific reference to nickel-cadmium cells, it being understood that its corresponding use with other suitable battery types will be apparent to those of ordinary skill in the art having knowledge of this disclosure.
In any event, as such batteries accept an applied charge, as through the application of a relatively constant current, their electrochemical potential or voltage exhibits a nonlinear change, with time, having a predetermined characteristic form
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