Electricity: battery or capacitor charging or discharging – Primary cell depolarization
Reexamination Certificate
1999-10-25
2001-06-05
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Primary cell depolarization
C320S132000
Reexamination Certificate
active
06242886
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to lead acid batteries, and in particular, relates to an apparatus and method for automatic recovery of sulfated lead acid batteries.
BACKGROUND OF THE INVENTION
A battery is a device that converts the chemical energy contained in its active materials directly into electrical energy by means of an oxidation-reduction electrochemical reaction. This type of reaction involves the transfer of electrons from one material to another. Batteries in the art commonly utilize electrochemical operations to store and release electrical energy.
FIG. 1
illustrates the electrochemical operation of a typical battery. Referring to
FIG. 1
, the negative electrode (anode
2
) is the component capable of giving up electrons, being oxidized during the reaction. It is separated from the oxidizing material, which is the positive electrode (cathode
1
), the component capable of accepting electrons. The transfer of electrons takes place in the external circuit
11
connecting the two materials and in the electrolyte
3
, which provides an ionic medium for the electron transfer in the battery
4
.
Certain types of batteries are rechargeable, such as lead acid batteries. A lead acid battery uses sponge lead for the negative electrode (anode
2
), lead oxide for the positive electrode (cathode
1
), and a sulfuric acid solution for the electrolyte
3
. The lead acid battery
4
is left in a charged condition when it is not being used. During discharge, the active material in the lead acid battery is converted into lead sulfate and the sulfuric acid solution is diluted, i.e., its specific gravity decreases. Lead sulfate is an insulator that inhibits the proper charging of the lead acid battery
4
. However, the lead acid battery
4
can be used after it is recharged.
To recover the lead acid battery, the lead sulfate is converted back to active material by charging the battery at a low current. If the lead acid battery is left in discharge for a long time, typically a few days, it becomes sulfated and difficult to recharge. The sulfated lead acid battery is discarded if it is not recoverable, which is wasteful and harmful to the environment.
Therefore, there is a general need in the art for an improved apparatus and method of recovering lead acid batteries. An efficient apparatus and method for recovering lead acid batteries, that avoids unnecessary waste, is needed.
SUMMARY OF THE INVENTION
The lead acid battery is stored by placing it in a charged condition when it is not in use. In storage, self-discharge occurs which causes the battery voltage to decrease. The internal resistance increases when the battery is left in storage for a long period of time due to the growth of lead sulfate crystals, especially if the battery is stored in a discharged condition. The lead acid battery is recovered for usage by charging the battery with a low constant current. As the lead acid battery is being charged slowly by a constant charge current, the battery voltage during charging approaches a minimum voltage in the battery recovery process. Then, the battery voltage gradually increases as the lead acid battery is being charged. As the recovery process is being implemented, the sulfate in the lead acid battery is converted to active material which also causes the battery voltage to decrease due to decreasing IR drop voltage. Due to the charging which causes the conversion of lead sulfate to the active material, the battery voltage increases.
According to the present invention, when it is detected that the battery voltage has reached the minimum voltage and begun to increase, the charge current is substantially increased (e.g., doubled) because the capability of the lead acid battery to accept a higher charge current has increased. As the charge current is increased, the recovery and charging of the lead acid battery are advantageously more expedient and efficient.
In an illustrative embodiment of the present invention, the internal resistance of the battery is measured. If it is above a recoverable limit, e.g., 5 ohms (&OHgr;), it is discarded. If it is below a normal limit, e.g., 0.2 ohms (&OHgr;), it is subjected to normal charging. If it is between these limits, the electrolyte level is checked and corrected if it is low. Then, a controlled charge of current, e.g., 0.5 amperes (A), is sent to charge the battery and the battery voltage is measured and compared to a minimum voltage. If the battery reaches the minimum within a preset time interval, e.g., one hour, the charge is increased, e.g., doubled. A test is then made to see if the charge current has exceeded a current limit. If it has not exceeded the current limit, the battery voltage is measured at the new level and, if it reaches another minimum, the charge is increased again. This is repeated until the battery has been charging for another time period, e.g., eight hours, or the current limit is reached, indicating that the battery recovery is completed and the battery is no longer sulfated. Then, normal charging is used to make the battery ready for use.
In another embodiment, if the battery voltage continues to increase after the predetermined period, the charging is stopped for a short period of time, e.g., five minutes, and then the process is repeated from the point of checking to see if the charge current has exceeded the limit. If the voltage is decreasing or remains the same, a check is made to see if the battery has reached the minimum and begun to increase. If it has, the charging is stopped for a second period of time, e.g., five minutes. Then, the process begins from the beginning, i.e., by measuring the internal resistance.
In an embodiment of the apparatus of the present invention, a computer or microprocessor is programmed to implement the process steps (as illustrated in the various embodiments herein) of the method of the present invention. The method steps can be advantageously reconfigured by reprogramming the computer or microprocessor, e.g., to implement a voltage control method as opposed to the embodiments in which the battery is charged by a controlled charge current.
In an embodiment of the voltage control method of the present invention, the lead acid battery is charged by a controlled charge voltage. The charge voltage is increased if the internal resistance of the battery is within a recoverable range. The charge voltage is increased until the battery current reaches a first current limit. Then, the battery is charged until the battery current reaches a second current limit, at which point the charge voltage is decreased. The charge voltage is also compared with a preset limit. The process steps of the voltage control method of the present invention are repeated until the charge voltage falls below the preset limit, at which point the battery is charged using normal charging. After the normal charging is complete, the battery is available for use.
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Gollomp Bernard P.
Palanisamy Thirumalai G.
Singh Harmohan
Allied-Signal Inc.
Tibbits Pia
Wong Peter S.
Yeadon Loria B.
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