Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2000-11-16
2001-07-10
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
Reexamination Certificate
active
06259231
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to battery chargers and, more specifically, to a rapid battery charger.
2. Description of the Prior Art
Battery chargers for lead-acid batteries typically apply a charge current to a battery cell or cells under charge. The charge current drives an electro-chemical reaction that causes lead ions to precipitate out of an electrolytic solution onto a metal plate. Once a maximum amount of lead is removed from the solution, the battery is said to be “fully charged.”
FIG. 1
shows a graph of a typical charging cycle for a battery. The x-axis
106
represents time and the y-axis represents both voltage
102
and current
104
. The charge cycle comprises an application of a charging current pulse
120
, a rest period
114
and the application of a depolarization pulse
116
. Several consecutive charge cycles may be employed to charge a battery.
Initially, when a current (represented by a dotted line on the graph) is applied to a fully discharged battery the voltage (represented by a solid line) across the battery terminals is low, but increases at a very high rate relative to time
110
. Eventually, the voltage levels off
112
and the rate of change, relative to time, approaches zero. At this point the efficiency of the charger is very low. This is due to the formation of a layer of lead-poor electrolyte forming around the metal plate to which the lead ions are precipitating. This layer is referred to as the “Helmholz” layer. As the Helmholz layer thickens, the rate of lead precipitation decreases. While one could apply a higher voltage to the charging current to increase precipitation, such a voltage would give rise to an increased level of heat production in the battery and, thus, a higher level of electrolyte evaporation.
The depolarization pulse
116
is applied to break up the Helmholz layer. Generally, the depolarization pulse
116
is a short pulse that forces the lead-poor electrolyte molecules away from the metal plate to which the lead is precipitating. Once the Helmholz layer is dissipated, normal charge current may again be applied with higher efficiency.
Many prior art chargers apply charging current pulses of fixed duration. During a portion
118
of the charging period
120
, characterized by a rate of voltage change relative to time approaching zero, the Helmholz layer is relatively thick and less efficient charging is taking place. During this portion
118
, most of the energy being applied to the battery is wasted in the form of heat.
Therefore, there is a need for a battery charger that senses when the rate at which voltage changes relative to time is near zero and that ceases to apply current near that time.
SUMMARY OF THE INVENTION
The disadvantages of the prior art are overcome by the present invention which, in one aspect, is a method of charging a battery cell, having a positive terminal and a negative terminal in which a charging current is applied to the battery cell. A voltage is measured between the positive terminal and the negative terminal. The charging current is no longer applied to the battery cell at a predetermined period subsequent to when the voltage changes at a rate, relative to time, that is not greater than the predetermined threshold.
In another aspect, the invention is a battery cell charger that includes a charger circuit capable of applying a charging current to the battery cell. A voltage sensor circuit measures a voltage between the positive terminal and the negative terminal of the battery cell. A charger control circuit is responsive to the voltage sensor and directs the charger circuit to apply the charging current to the battery cell while the voltage changes at a rate, relative to time, that is greater than a predetermined threshold. The charger control circuit also directs the charger circuit to cease to apply the charging current to the battery cell at a predetermined period subsequent to when the voltage changes at a rate, relative to time, that is not greater than the predetermined threshold.
These and other aspects of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the following drawings. As would be obvious to one skilled in the art, many variations and modifications of the invention may be effected without departing from the spirit and scope of the novel concepts of the disclosure.
REFERENCES:
patent: 3617851 (1971-11-01), DuPuy et al
patent: 5694023 (1997-12-01), Podrazhansky et al.
patent: 5808447 (1998-09-01), Hagino
patent: 5945811 (1999-08-01), Hasegawa et al.
patent: 5998968 (1999-12-01), Pitman et al.
patent: 6060865 (2000-05-01), Chen
Bockhop Bryan W.
Bockhop & Reich, LLP
R G Technology Ventures, LLC
Tso Edward H.
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