Cyclical battery charger with incremental and decremental...

Electricity: battery or capacitor charging or discharging – Diverse charging or discharging rates for plural batteries

Reexamination Certificate

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Details

C320S160000

Reexamination Certificate

active

06333619

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to batteries and, more specifically, to a cyclical battery charger capable of providing incremental and decremental currents and a method of operation thereof.
BACKGROUND OF THE INVENTION
Electronic systems, whether in telecommunications, data processing or other industries requiring operational capability at all times, necessitate the use of reserve power to accommodate the times when an AC power source outage occurs. This typically implies that a battery or a collection or “string” of batteries is required to supply the needed interim power. Often, the environment in which the batteries must operate provides harsh conditions that are extremely detrimental to them. Therefore, a battery monitoring system is typically used to monitor and condition them. The goal of the battery monitoring system is to protect the batteries from being damaged, provide a conditioning or recharging environment and ultimately extend useful battery life.
Parameters that are detrimental to batteries include: a large or uncontrolled charge current, a constant value of charging voltage that is too high, a high battery temperature that causes the battery to vent gas, shorted battery cells that force others to overcharge and conditions that overly discharge the battery. Conventional battery monitoring and conditioning systems are focused on simplicity of operation regardless of any degenerative impact that they may have on the batteries themselves. For example, a conventional battery monitoring and conditioning system may provide a single value of charging current during an initial phase of charging. This single value of charging current is typically maximized to assure that the batteries are charged quickly.
The maximum value of this current is often limited only by the internal resistance of the batteries themselves. A large value of battery charging current produces a high likelihood that the batteries will overheat. Overheating of the batteries causes their internal resistance to decrease further thereby allowing the charging current to further increase. This process, if unchecked, often produces a thermal runaway condition that either partially or severely damages the batteries. Even if the batteries do not enter a thermal runaway condition, a “thermal event” may exist wherein one or more of the batteries becomes overheated and vents gas to the environment causing those batteries to dry out over time.
After the batteries have reached a fully charged state under these conditions, the charge current is typically reduced in value, and the battery voltage usually decreases to a maintained value. Over time, battery cells that have been damaged by this charging process may become shorted. A shorted battery cell can no longer properly store energy, forces other batteries to overcharge and therefore usually requires that the battery or batteries be removed and discarded. Although simple in operation, this type of battery monitoring and conditioning system treats all batteries in the same way and usually monitors the voltage condition of the battery only to determine the presence of a shorted cell.
Accordingly, what is needed in the art is an improved way to monitor and condition batteries that avoids thermal events and allows the batteries to reach their full energy capacity.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides a battery charger, a method of charging a battery and a battery plant incorporating the battery charger or the method. In one embodiment, the battery charger includes: (1) a battery voltage monitor that measures a voltage of a battery and (2) a charge current generator, coupled to the battery voltage monitor, that provides an incrementally adjustable charge current to the battery based on the voltage.
The present invention therefore introduces the broad concept of basing adjustments to charge current levels on battery voltage, such that the rate at which the battery charger charges a battery depends upon the response of the battery. The battery charger can monitor any voltage associated with the battery. However, in an embodiment to be illustrated and described, the battery charger monitors a voltage of a battery at its terminals. The voltage measured can be instantaneous, a change in voltage over time (a slope) or any derivative thereof.
In one embodiment of the present invention, the charge current generator operates in an initial charge mode in which the incrementally adjustable charge current assumes one of at least two intermediate levels based on the voltage. In an embodiment to be illustrated and described, the battery charger assumes one of four intermediate levels, in addition to zero and a maximum level. The intermediate and maximum levels can be set at any absolute value and do not need to be evenly spaced apart.
In one embodiment of the present invention, the charge current generator operates in an initial charge mode in which the incremental adjustable charge current decrements each time the voltage reaches an upper limit. The upper limit can be set at any absolute value, and may be caused to change over time in some embodiments of the present invention.
In one embodiment of the present invention, the charge current generator operates in a maintenance mode in which the incrementally adjustable charge current toggles from zero to a single higher value when the voltage reaches a lower limit. In an embodiment to be illustrated and described, the single higher level is one of the four illustrated intermediate levels, although this need not be the case.
In one embodiment of the present invention, the charge current generator increases the lower limit over time. The lower limit can increase to accommodate an increase in capacity of the battery over time. The present invention does not require that the lower limit rise, and is not limited to a particular time to initiate a rise or rate of rise.
In one embodiment of the present invention, the charge current generator operates in a maintenance mode in which the incremental adjustable charge current toggles to zero from a single higher value when the voltage reaches an upper limit. In an embodiment to be illustrated and described, the upper limit is the same as in the initial charge mode.
In one embodiment of the present invention, a discharge event causes the battery charger to shift from a maintenance mode to an initial charge mode . The discharge event may be defined by a battery voltage excursion of a given minimum magnitude or rate or over a given period of time.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.


REFERENCES:
patent: 3614583 (1971-10-01), Burkett
patent: 5461297 (1995-10-01), Crawford

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