Electricity: battery or capacitor charging or discharging – Battery or cell charging – With thermal condition detection
Reexamination Certificate
2001-08-07
2002-12-03
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell charging
With thermal condition detection
Reexamination Certificate
active
06489751
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to battery charging systems and more particularly to battery chargers and rechargeable battery packs.
BACKGROUND OF THE INVENTION
Rechargeable batteries are well known in the prior art. Rechargeable batteries are capable of being charged prior to initial use and recharged after being discharged. Generally, rechargeable batteries are charged by a battery charger having a power supply that can provide a supply of DC current. A rechargeable battery accepts the electrical current and converts it into chemical energy. As long as the rechargeable battery is capable of converting the electrical current into chemical energy, the rechargeable battery will not significantly rise in temperature. When a rechargeable battery is at full capacity, it is incapable of converting the charge current into chemical energy and it dissipates any continuing charge current as heat. The heat generated by a rechargeable battery is an ideal parameter to sense that it has reached a fully charged state.
A typical low-cost battery charger provides a charging current that is a relatively low current to a rechargeable battery such that it can be sustained indefinitely without damaging the battery. This low current, typically between 25 milliamps and 100 milliamps, will safely charge a battery from a discharged state to a fully charged state in approximately 4 to 12 hours. This low current provided by the low cost battery charger is sometimes referred to as a trickle charge. The trickle charge current can be set to a level where the battery can safely dissipate excess current into heat without overheating the battery. Generation of excessive heat in a rechargeable battery will cause it to breakdown and reduce its useful lifetime. A disadvantage to using a low current and low cost battery charger is that it requires charging a battery for a relatively long period of time in order to reach a fully recharged state. Using certain precautions, rechargeable batteries can be charged at a faster rate using higher charging currents.
A rechargeable battery can be charged at higher rates provided that safety precautions are taken to prevent overheating of the battery thereby preventing a possible fire, injury to a user, or damage to the battery or the battery charger. Preventing injury to a user is particularly important when a charging system is utilized by children to recharge batteries that are utilized in toys. Additionally, as new fast charge technology is applied to rechargeable batteries for use within toys, safety precautions become very important as a result. A battery charger should assure that a rechargeable battery is not charged at an excessively high rate and that the charging current is removed or reduced, such as to a trickle charge rate, shortly after the battery reaches its fully charged state. The charge rate refers to the level of charge current and the time to recharge a discharged battery. A charge rate is excessive if it exceeds the rate at which a rechargeable battery can convert the charge current into chemical energy. This occurs when the charging current level is higher than the maximum charge current rated for a given battery type and capacity. For example, a typical 50 milliamp-hour Nickel-Cadmium (NiCad) battery can safely be charged up to a charging current level of 200 milliamps while a 700 milliamp-hour NiCad battery can be safely charged up to a charging current level of 2.8 amps. Typically, NiCad battery construction will allow for a battery cell to be recharged at four to ten times its hour rating of battery capacity. Battery manufacturing techniques vary from manufacturer to manufacturer as well as from cell type to cell type which dictates the maximum charge rate for each cell. If the charge rate is excessive, the battery produces heat to dissipate the energy provided by the excessive charge current level. Regardless of the charge current level, when a battery reaches its fully charged state it is no longer capable of converting the charge current into chemical energy. In this case, the battery dissipates the extra charge current as heat and the current should be removed or reduced such as to a trickle charge current in order to avoid damage, maintain battery life, and protect persons and property from harm.
There are a number of types of battery chargers available that will provide for higher rates of charging. These battery chargers are referred to as high-speed chargers or fast chargers. A number of these fast chargers attempt to automatically detect the battery capacity and set an appropriate charge current level. However, fast chargers which attempt automatic detection of battery capacity usually never charge at their fastest charge rate. Instead, because there are so many batteries of varying types from different battery manufacturers having different specifications, typically the lowest battery specification is used to avoid damage. Other fast chargers require that an operator manually select the proper charge current level for the battery that is to be charged. Typically these manually set fast charges allow a charge rate and charge time to be set at the discretion of the operator. An operator can inadvertently set the battery charging parameters to dangerous levels which could result in damage to the battery charging equipment or the operator or others nearby. Others battery chargers are dedicated to a single battery type and capacity with the battery charger designed to supply current levels required for the single battery type. These dedicated chargers typically have a charge rate set to recharge a rechargeable battery outside of an hour or more. The foregoing charge current levels may include a maximum level for a fast charge and other lower levels such as a trickle charge current level for slow charge. To avoid charging a battery after having reached its fully charged state, a number of methods may be employed to provide automatic charge shut-off.
The reader is referred now to
FIG. 1
illustrating a cutaway perspective view of a prior art rechargeable battery pack
100
. Rechargeable battery pack
100
includes a number of rechargeable batteries
101
coupled in series to generate increased electrical capacity over that of a single rechargeable battery. Typically battery cells are coupled in series to attain the appropriate voltage level for the application. Each rechargeable battery
100
has a positive terminal and a negative terminal. In coupling the battery in series, the positive terminal of the first battery is coupled to the negative terminal of the second battery and the positive terminal of the second battery is coupled to the negative terminal of the third battery and so on. A connecting wire
103
is coupled to the negative terminal of the first battery in the series at one end and the negative battery pack contact
105
at its other end. A connecting wire
104
is coupled to the positive terminal of the last battery in the series at one end and the positive battery pack contact
106
at its other end. In some instances, a battery pack
100
may include a thermistor
110
within the battery pack housing
102
for sensing the temperature of the batteries. The resistance value of this thermistor is representative of the heat generated during a recharging process. The battery pack
100
includes the sensor contacts
115
and
116
that connect to the thermistor
110
by connecting wires
117
-
118
respectively.
Prior art methods of providing automatic shut off usually evaluate the rate of change in battery voltage over time (−delta V/delta time) or by evaluating the rate of change in battery temperature over time (delta T/delta time) and compare it with battery specifications. The battery temperature in prior art battery packs
100
is measured by the included thermistor
110
. The measurement of temperature provided by the thermistor
110
is signaled to a battery charger through the wires
117
-
118
and sensor contacts
115
-
116
. This type of battery charger will typically include a microprocessor to eva
Farley Brian
McKeefery James
Small David
Blakely & Sokoloff, Taylor & Zafman
Shoot the Moon Products II, LLC
Tibbits Pia
Tso Edward H.
LandOfFree
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