This invention relates to battery charging systems and more particularly to battery chargers and rechargeable battery packs.
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.
One or more rechargeable batteries are oftentimes packed together in series as a rechargeable battery pack to provide a desired operational voltage and current. The rechargeable battery packs are often used to power battery powered devices such as toys which are oftentimes operated by children. The rechargeable battery packs are removable from a battery powered device for a number of reasons. A reason for providing a removable rechargeable battery pack is that one battery pack can be remotely charged while another is being used in the battery powered device. The typical rechargeable battery pack has one or more rechargeable batteries coupled in series together. Two terminals of the rechargeable battery pack are coupled to each end terminal of the series of rechargeable batteries. At least one end terminal of the series of rechargeable batteries is typically coupled to one of the terminals of the battery pack by a wire. The rechargeable batteries are encased into a rechargeable battery case with a positive battery pack terminal protruding through an opening in one side of the case and a negative battery pack terminal protruding through another opening in the other side of the case in order to make contact with charging terminals of a battery pack charger. The rechargeable battery case is typically made of a plastic material that is insulating so as not to short to metal electrical contact points.
The typical rechargeable battery pack case is rectangularly shaped. The typical width of a rechargeable battery pack case is approximately the length of a rechargeable battery when rechargeable batteries are oriented therein side by side without stacking. The typical length of a rechargeable battery pack case is approximately the sum of the diameters or widths of rechargeable batteries held within the case for rechargeable batteries sitting side by side. On the left and right sides of the rechargeable battery pack case, there is a base edge and a top edge. The base edge has a narrower region than the typical width of the rechargeable battery pack case. To hold the rechargeable battery pack into a battery powered device or battery charger, the typical rechargeable battery pack case has multiple L shaped tabs along the base edge of one side and three mirrored-L shaped tabs along the base edge of the opposite side. The multiple L shaped tabs and the multiple mirrored-L shaped tabs protrude from the narrower region of the base edge to approximately have the typical width of the typical rechargeable battery pack. The shape and foot of the L and mirrored-L shaped tabs hold the battery pack in contact to the terminals of the battery powered device or battery charger.
The typical battery pack charger has open faced surfaces to couple with the rechargeable battery pack. The battery pack charger includes two opposing surfaces one having a positive electrical contact protruding through it and another having a negative electrical contact protruding through it. These electrical contacts are accessible to a user and typically do not have any safety concerns as the voltage on these terminals is below 24 volts which is considered a safe voltage. This low voltage is typical of low current chargers in that an isolation transformer is used to convert the 120 volt AC-line power into a lower voltage that is typically 12 volts AC. Higher current power systems are required if a battery is to be charged at a higher rate, which means a higher charge current. Higher current power supplies in some cases cannot employ an isolation transformer to step the 120 volt AC-line power down to a safe voltage. This is because an appropriate sized isolation transformer may be very expensive, large and heavy. Without an isolation transformer, the terminals of the charger may be unsafe to touch because a high voltage may be present at the electrical contacts. Touching just one terminal can result in shock because a current may be able to travel from the non-isolated electrical contact of the charger through a human body to ground.
When engaged, the rechargeable battery pack is not enclosed by the typical battery pack charger. The surfaces of the rechargeable battery pack are grabable by a user to engage or disengage it with the battery pack charger. To engage with a battery pack charger, the rechargeable battery pack is slid against a flat surface of the battery pack charger between the two opposing surfaces, orthogonal to the flat surface and separated by the width of the rechargeable battery pack, in order to make mechanical and electrical connections with the charger. The electrical and mechanical connections are made on the sides of the rechargeable battery pack. One of the two opposing surfaces of the battery pack charger has a negative electrical contact protruding through side to make electrical connection to the contact on one side of the rechargeable battery pack and another one of the two opposing surfaces has a positive electrical contact protruding through so as to make electrical connection with the contact on the other side of the rechargeable battery pack.
To make mechanical connections, the typical battery pack charger includes an upside down L shaped tab and an upside down mirrored-L shaped tab in the respective opposing surfaces. The battery pack case of the rechargeable battery pack, uses the L and mirrored-L shaped tabs closest to the terminals of its three L and mirrored-L shaped tabs to mate with the battery pack charger. The upside down L shaped tab of the battery pack charger mates with the first mirrored-L shaped tab of the rechargeable battery pack on one side. The upside down mirrored-L shaped tab of the rechargeable battery pack mates with the first L shaped tab of the rechargeable battery pack on the opposite side. The mating between these tabs, keeps the rechargeable battery pack from moving further forward, keeps it aligned with the electrical contacts and keeps the rechargeable battery pack coupled in place to the battery pack charger in one direction.
To hold the rechargeable battery pack in place in an orthogonal direction, the battery pack charger includes a spring loaded latch mechanism having a catch and a user push button. The spring loaded latch interfaces to one side only of the rechargeable battery pack when inserted. With the rechargeable battery pack being inserted, as the first mirrored-L shaped tab passes over the catch of the spring loaded latch, the catch of the spring loaded latch is depressed into the charger. After the end of the first mirrored-L shaped tab has passed, the catch of the spring loaded latch is released to protrude up behind the first mirrored-L shaped tab in order to hold the rechargeable battery pack to the battery pack charger. To release the rechargeable battery pack from the battery pack charger, a user depresses the button of the spring loaded latch to depress the catch so the first mirrored-L shaped tab can clear the catch as the rechargeable battery pack is pulled away by a user from the battery pack charger.
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.
Rechargeable batteries in a rechargeable battery pack can be charged at higher rates using higher current levels than that used at slow charge rates. However when fast charging, safety precautions should be taken to prevent overheating of the batteries 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. If no safety precautions are taken, then rechargeable battery packs should only be charged at slow rates using low current levels.
Some safety precautions for fast charging that can be taken is to assure that a battery charger will not charge a rechargeable battery 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 two 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.
It is desirable to provide a fast charge battery charging system having safety features to avoid damage, maintain battery life, and protect persons and property from harm.
The present invention includes the methods, systems and apparatus which are briefly summarized in the claims.
Briefly, a battery charging system including a rechargeable battery pack and a battery pack charger is disclosed. The rechargeable battery pack and the battery pack charger include mechanical safety mechanisms to safely charge the rechargeable battery pack using at least one fast charge rate. The rechargeable battery pack and the battery pack charger are mechanically and electrically coupled together in order to charge the rechargeable battery pack.
The rechargeable battery pack includes an opening to allow a temperature sensor to directly sense the temperature at a terminal case of a rechargeable battery cell in the rechargeable battery pack. A temperature sensor is used to determine when to automatically cutoff charging at the at least one fast charge rate. The rechargeable battery pack further includes one or more key slots along a rear edge in order to distinguish it from others. Additionally, rectangular guide tabs in the rechargeable battery pack of the present invention allow it to be backward compatible. The rechargeable battery pack of the present invention can be charged in former battery pack chargers and used to power former battery operated devices.
The battery pack charger includes one or more key tabs in a charger door that need to mate with the one or more key slots in the rechargeable battery pack in order for the charger door to close into a closed position and begin charging. The combination of the one or more key tabs with the one or more key slots provides a safety mechanism to assure that the appropriate battery pack is inserted which can be safely charged.
The battery pack charger further includes a high current charger power supply which is not electrically isolated from AC line power. The battery pack charger due to the non-isolated power supply design includes a safety switch mechanism that facilitates the safety system provided by the key slots in the battery pack and tabs on the charging door to avoid electrical shock to a user in the event that a user touches one of the charging terminals when a rechargeable battery pack is not inserted into the charger. The safety switch mechanism includes at least one switch to switch one circuit or a pair of switches to switch two circuits. In one embodiment the switch (or pair of switches) is a spring switch with a leaf spring contact or button. In another embodiment, the switch (or pair of switches) is a micro-switch with a leaf spring lever activation. In yet another embodiment, the switch (or pair of switches) is formed of a conductive strip and a spring loaded conductive strip. One lever arm or and a pair of lever arms of the charger door of the battery pack charger are used to activate the safety switch mechanisms. The one or more lever arms activate (i.e. close, turn ON or switch ON) and deactivate the one or more switches (i.e. open, turn OFF or switch OFF) by applying or releasing a pressure or force on a contact point of the leaf spring contact, the button, the leaf spring lever, or the spring loaded conductive strip. When the charger door is closed, the lever arms push on the leaf spring contact, the button, the leaf spring lever, or the spring loaded conductive strip in order to close the switch to provided a closed circuit. With the charger door in an open position there is no pressure from the lever arm on the leaf spring contact, the button, the leaf spring lever, or the spring loaded conductive strip. Therefore, the safety switches are not closed and provide an open circuit when the charger door is in the open position. When the charger door is in a closed position, the closing of the safety switch mechanism (or mechanisms) allows power to be supplied to a rechargeable battery pack that is inserted into the battery pack charger.
The battery pack charger further provides rectangular guide tabs on sidewalls of an inner housing that allow the rectangular guide tabs of the rechargeable battery pack to slide under. The rectangular guide tabs of the battery pack charger further distinguish the type of rechargeable battery packs that can be fully inserted therein for safe charging.
The battery pack charger further includes a charger power supply on a printed circuit board with the appropriate circuitry to charge the rechargeable battery pack at the at least one fast charge rate. The battery pack charger includes a temperature sensor coupled to the printed circuit board at one end that reaches through the opening in the rechargeable battery pack to directly sense battery temperature at a terminal case of a rechargeable battery cell in the rechargeable battery pack.