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Battery Currents – Introduction and Working Status
Batteries are vital in today's world. Without batteries, the world would take a trip back in time. Imagine a world without cell phones, torches, hearing aids, electric cars, laptops, calculators, watches, heart pacemakers, transistor radios, etc. We would still be depending on steam energy or other ways of making portable energy.
Batteries, though small, have a far greater impact in almost all sectors of the economy of the world today. These products give us a steady supply of electrical energy whenever and wherever we want or need it. Despite the varying sizes and types of batteries in the market, they still serve the purpose of serving as people's micro power plants.
Below, we discuss all we need to know about how a battery converts chemical energy to electrical energy. We look at battery charging current, maximum currents, and direct currents. Let's get started.
Battery Charging Current
A battery has a charging current. Current is described as the rate of time of flow of an electric charge within a battery. There are three different methods of charging a battery, namely: constant current, constant voltage, and a combination of constant voltage and constant current.
A battery's voltage is the energy per unit charge. A constant voltage will allow the full current of a charger to flow within a battery when charging until the power supply is at a pre-set voltage. Once the voltage level is reached, the current will slow down to a minimum value. When you leave your battery plugged into a power source and charger, it will remain at the float voltage. It will continue trickle charging to compensate for normal battery self-discharge.
Here is whereby you charge the battery with the current level at 10% of the maximum battery rating. When using this method, one has to set a timer to notify when the battery is fully charged to void overcharging it.
Constant Voltage / Constant Current
In this method, the charger will limit the amount of current to a pre-set level until the battery reaches the pre-set voltage level. The charging current will then reduce as the battery becomes fully charged. Lead-acid batteries use this method of charging. It is the most preferred method as it helps preserve a battery's maximum life and capacity.
To be able to know the charging current you should use on your battery. You have to know the voltage of charging and the battery capacity, which is indicated by Ah. Therefore, the charging rate will depend on the type of battery you have. For example, a lead-acid battery will be charged at about 25% of the capacity.
Battery Max Currents
It is reasonable for frequent users of batteries, for example, car batteries, to understand and consider the maximum capacity a battery can safely deliver. The capacity of your battery will depend on a lot of factors and things, the foremost being the chemistry of the battery. The maximum discharge rate of a battery is also used to measure its capacity. A battery's maximum discharge rate is usually specified in terms of C. C is the capacity of the battery divided by hours it takes to discharge. Let's take an example of a 2Ah battery. In case the battery has a maximum discharge rate of 10C, the maximum current will be 20 amps. Therefore, by knowing the capacity of your battery and the time it takes to charge it, you will be able to know the maximum current your battery can hold.
Let's take an example of batteries with different chemical compositions and how much charging voltage they will need;
A 12V lead-acid battery is usually used in a car, and such a battery will have a maximum charging voltage of 14.5V.
A NiCd or NiMH 12v pack will mean it has 10 cells within it. It will need a 15 to 16V for charging.
A lithium-ion battery with a 3.7V per cell will need a charging voltage of about 4.2V. The battery is generally rated at a 1C maximum charge rate.
The maximum capacity of a battery is found at a low C-rate. When charging or discharging at a higher C-rate, it will reduce the life and capacity of the battery.
Battery manufacturers often publish data sheets that show graphs of capacity versus C-rates of a battery. The C-rate is used on batteries to indicate the maximum current that a battery can deliver in a circuit.
Battery Direct Currents
All batteries produce direct current. It is the unidirectional flow of electrical charge within a battery that provides constant voltage or current. As long as the direction of flow does not change, a battery's voltage and current may vary over time. Most of our small devices and electronic gadgets use the direct current flow. Such devices include laptops, radios, cell phones, flashlights, hybrid and electrical vehicles. Apart from this, solar cells, some types of generators, and fuel cells also generate a direct current flow.
Direct current is produced as a result of an imbalance between the electrical charges within a battery. A battery has cathode and anode terminals that react differently to the electrolyte fluid. The negative terminal will gain electrons while the positive terminal loses electrons and becomes positively charged. When the two terminals are connected electrons can pass through the wire to try and balance the electrical charge. Due to this movement, the electrons lose energy which is then converted to heat that is used to power our devices. Since this energy comes from the chemical energy of the electrolytes, the chemical energy will, at last, deplete leading to a flat battery. This is how a direct current flow is formed.
DC batteries are beneficial in the motor vehicle industry. All cars including electric vehicles use DC batteries. These batteries can transfer more power with less electrical losses over a long distance. They are known to provide higher efficiency at a lower cost. Despite this advantage, DC batteries are known to wear out over time after going through a lot of different charge cycles and reaching their expected lifetime. Therefore, one may need to change a DC battery after it reaches its maximum life capacity.