If both the (dis)charge current and the battery capacity in the C-rate ratio is multiplied by the battery voltage, the C-rate becomes a ratio of the (dis)charge power to the battery's energy capacity. Since the unit of the C-rate is typically implied, some care is required when using it to avoid confusing it with the battery's capacity to store a charge, which in the SI has unit coulomb with unit symbol C.
Likewise, for the same battery a charge current of 250 mA corresponds to a C-rate of C/2, meaning that this current will increase the state of charge of this battery by 50% in one hour. The C-rate is never negative, so whether it describes a charging or discharging process depends on the context.įor example, for a battery with a capacity of 500 mAh, a discharge rate of 5000 mA (i.e., 5 A) corresponds to a C-rate of 10C, meaning that such a current can discharge 10 such batteries in one hour. While rarely stated explicitly, the unit of the C-rate is h −1, equivalent to stating the battery's capacity to store an electrical charge in unit hour times current in the same unit as the charge or discharge current. The C-rate is defined as the charge or discharge current divided by the battery's capacity to store an electrical charge. For public access, installation of such chargers and the distribution support for them is an issue in the proposed adoption of electric cars.Ĭharge and discharge rates are often given as C or C-rate, which is a measure of the rate at which a battery is charged or discharged relative to its capacity. Electric vehicles ideally need high-rate chargers. Such batteries require active monitoring of the battery to protect it from overcharging. High-rate chargers may restore most capacity much faster, but high rate chargers can be more than some battery types can tolerate. Slow battery chargers may take several hours to complete a charge. Lithium-ion batteries cannot handle indefinite trickle charging.
Some battery types cannot tolerate trickle charging attempts to do so may result in damage. Ī trickle charger provides a relatively small amount of current, only enough to counteract self-discharge of a battery that is idle for a long time. The charger may have temperature or voltage sensing circuits and a microprocessor controller to safely adjust the charging current and voltage, determine the state of charge, and cut off at the end of charge.Ĭhargers may elevate the output voltage proportionally with current to compensate for impedance in the wires. Other battery types cannot withstand over-charging, becoming damaged (reduced capacity, reduced lifetime), over heating or even exploding. Other battery types use a timer to cut off when charging should be complete. Simple chargers of this type must be manually disconnected at the end of the charge cycle. Some battery types have high tolerance for overcharging (i.e., continued charging after the battery has been fully charged) and can be recharged by connection to a constant voltage source or a constant current source, depending on battery type.
The charging protocol (how much voltage or current for how long, and what to do when charging is complete) depends on the size and type of the battery being charged. A battery charger, or recharger, is a device that provides electricity to convert into stored chemical energy for storage in an electrochemical cell by running an electric current through it.
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