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(449)Storing electricity is one of the greatest challenges of today, in the era of mobile devices and renewable energy. This product category includes mainly batteries that are used with the equipment from the former field. These are items intended for portable devices, remotely controlled, self-propelled robots, but also substitutes for ordinary AA and AAA batteries, cell packages for high-current devices (power tools, RC models), as well as components which may be of interest primarily to manufacturers of electronic equipment, i.e. batteries intended for factory installation inside various devices or even PCB mounting. Depending on the product they are looking for, the buyers will ask themselves one of the following questions...
A rechargeable battery – what should you pay attention to?
For many years, "rechargeable batteries", i.e. rechargeable equivalents for standard batteries, have been a realistic and cost-effective alternative. The purchase of a set of AA or AAA batteries and a universal charger is an economic, convenient and ecological solution. It is also an excellent and universal idea for a practical gift. A common mistake made by consumers is buying batteries that are cheaper but have a smaller capacity. It will be a cost-effective choice only in the case of powering devices with low energy consumption (wireless mice and keyboards, RTV remote controls, clocks). For other equipment, the battery will need frequent charging and will wear out faster. Note that the nominal voltage of AA and AAA batteries is lower than, for example, in the case of alkaline batteries (1.2V and 1.5V, respectively). Older devices may not work properly when powered by rechargeable cells. Note! Mixing different batteries, which all manufacturers of electrical equipment warn against, can be harmful. It can be extremely dangerous in the case of rechargeable batteries! It can cause serious damage to the equipment and even damage to health (burns).
How to choose a replacement for a rechargeable battery?
It happens that small household devices equipped with rechargeable begin to get discharged more and more often and/or do not work properly, despite proper maintenance. If the device offers easy access to the battery installed inside, we can try to replace it. In the TME catalogue, we offer a number of packages that will replace batteries used in cordless telephones, shavers, electric toothbrushes, etc. However: if we do not know the detailed parameters of the package being replaced (capacity, type, voltage, output), we should research for those or analyze the circuit carefully. Otherwise, we may cause permanent damage to the equipment (e.g. burnout of the voltage stabilizer, motor failure, etc.). Fortunately, most brand-name cells and their packages are described in detail in the specifications printed on the battery case / packaging.
What type of rechargeable battery should you choose for the project?
Choosing a battery for your project is not an easy task. You can even say it is the art of compromise. The type of cells used will have a direct impact not only on the operation of the device, but also on its structure and the whole circuit. Therefore, let's briefly discuss the issues that require consideration at the design stage.
Which parameters of rechargeable batteries are crucial?
Unfortunately, the answer to this question is: all of them. Even such an insignificant matter as the type of pins can significantly affect the implementation of the project. The manufacturer (or even an individual constructor) should decide whether the device construction process should include, for example, the stage of spot welding of lithium-ion cells, or maybe if it is better to use an already made Li-Po package? If the consumer is able to replace the battery himself or herself, wouldn't it be better to opt for a standard, widely available format? Even the mass (and especially the center of gravity) of the end product will depend heavily on the energy source used.
Size and capacity
The highest "density" of stored energy is obtained in lithium-polymer batteries. However, their use is associated with a number of complications, which are discussed below. When using lithium-ion cells, it is worth considering the use of their less popular formats, e.g. shorter or thinner cylinders, which will allow for better use of space in the housing of the target device. Unfortunately, in any case, the cell capacity will be strictly reliant on its volume.
Voltage and intensity
Even the finest DC/DC converters do not reach 100% efficiency. Each converter placed in the circuit will waste energy and generate heat. It may seem appealing to place many parallel-connected cells in the device – it allows to achieve high amperage (this will be important when powering electromechanical components). However, the effect of such a solution may be the necessity to use the step-up converter, e.g. for the needs of a backlit LCD – this, on the other hand, will result in a significant energy consumption and a decrease in the service lifespan of the device. Moreover, if a microprocessor system (e.g. a single-board computer) is used, the device will still contain a number of converters and voltage stabilizers necessary for the operation of the central unit and its components. That is why it is important to choose such a package of cells (and circuit elements) that will enable the optimal powering of the entire system, preferably with the use of a single stabilizer (ideally, this will be a stabilizer coupled with a charge controller and balancer, but this is not always possible).
Types of rechargeable batteries – brief comparison
As each type of batteries has its own specific characteristics, here is a brief comparison of these technologies.
Lithium-Polymer rechargeable batteries
These are cells with an exceptionally high ratio of stored energy to volume, they provide high intensity current, and the packages can be formed into cuboidal solids of any size. They are used in compact products and where it large amounts of energy need to be provided in a short time (for example, the so-called car boosters, allowing the car to start despite being discharged). Unfortunately, cells of this type are also fragile, and in the event of a package breach, overheating, incorrect charging or even dampness – high instability. Li-Pol packages are factory-equipped with a balancer system that protects the product against misuse. However, this circuit does not guarantee full safety. The lithium-polymer battery charge controller must constantly monitor the temperature of the cells. Deep discharge of the package (or long-term storage in conditions other than specified by the manufacturer) may lead to degradation, irreversible damage and deformation.
Lithium-Ion rechargeable batteries
It is one of the most popular solutions available on the market. Li-Ion cells are characterized by long lifespan and easy maintenance. They charge in two stages: first, by maintaining constant current, and finally by constant voltage. Charge controllers and balancers for lithium-ion cells are widely available and inexpensive (however: it is best to choose a charger based on one of the systems from well-known and proven manufacturers). They are relatively resistant to mechanical factors, although thermally "sensitive". When bundling them into packages, avoid soldering the wires directly to the battery terminals – spot welders are a more and more popular choice for this purpose. Lithium-Ion cells can deliver a very high current (which also means they will be dangerous in the case of a short circuit). Their size is most often described as a series of numbers, e.g. 18650. It is a method of indicating the dimensions of the battery. The first two digits indicate its diameter in millimeters, the last three the length in tenths of a millimeter. Hence: 18650 is a cylinder with a diameter of 18mm and a height of 65mm. Fun fact, the Li-Ion 14500 cell has the same size as the AA format battery, so standard battery baskets can be used for their assembly and bundling.
LiFePO4 rechargeable batteries
Lithium-Iron-Phosphate cells are often referred to as the successors of the Lithium-Ion technology, but LiFePo4batteries do not contain cobalt in their electrodes. They are characterized by a longer service lifespan, greater stability and comparable electrical parameters. An additional benefit is their low self-discharge current (i.e. they remain charged for a relatively long time). The manufacturing process allows for the production of these batteries with terminals in the form of screws, which facilitates and speeds up the assembly and connection of cells. It also ensures low resistance of connections and their good current parameters.
Ni-MH rechargeable batteries
Its full name is "Nickel-Metal Hydride" rechargeable batteries. They are often used in consumer battery formats. They require pulse charging (ideally in a processor charger) as being connected to a DC source may be harmful for them. This type of cells is also sensitive to deep discharge.
Ni-Cd rechargeable batteries
Nickel-Cadmium cells are similar to Ni-MH cells in terms of structure, application and electrical parameters, although their energy density is lower. It should be remembered that these types of batteries demonstrate the so-called "memory effect". In other words, their capacity will degrade, if they are not regularly discharged and fully charged. The most important information for the potential buyer will be the fact that this type of batteries is currently withdrawn from TME's offer due to environmental reasons.
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