Owners of electric vehicles have a bit more extra task at hand when they need to fill up their EV’s batteries. Charging a battery is not as straight forward as filling up the fuel tank of a car. Typically the charging can last up to 8 hours or as little as 30 minutes depending on the type of charger used and the capacity of the EV’s battery. Although theoretically, it is possible to charge electric vehicles wherever there are standard power outlets, fast charging times can only be achieved by dedicated charging stations.
Electric vehicles use rechargeable batteries such as lead-acid, Nickel-metal hydride (NiMH), or Lithium-ion batteries. The batteries power the electric motor driving the vehicle by releasing the chemical energy stored within them in the form of electricity. Battery recharging works by sending electricity back in to reverse the chemical reactions by using a charger. Although the process sounds simple, there is some resistance offered up by the battery to take in the charge, and this resistance gets stronger as batteries start filling up with energy. Hence the first 75% or so of the battery gets recharged quickly, and the rest take a while to fill up.
Most regular chargers use a constant current or a constant voltage and ‘trickle’ the charge towards the end to top off the battery over a long period. This means the cells would take a couple of hours to charge to their full capacity. A rapid charger works by boosting the amount of energy going into the battery while smartly managing the charging parameters to keep it safe. It is, therefore, able to give fast charging times in the range of 30 minutes to one hour to fill the battery to about 80%.
Electric vehicle charging systems are a lot more advanced when compared to conventional battery chargers, although their primary function is the same. They need to load energy into the batteries as fast as the batteries can permit and monitor the battery parameters such as voltage and temperature during the charging process for safety purposes.
Typically a charging set up involves a wall charger or a charging station that plugs to the electric grid and safely allows electricity to flow to the car. To make it safer and more reliable, and Electric Vehicle Supply Unit (EVSE) is used in between the charger and the car. The EVSE is a wall-mounted box that regulates the recharging of EV batteries by acting as two-way communication and sets the right charging current based on what the battery can take and what the charger can provide. It offers several safety features to protect from power outages, excess loads, faults, and short circuits. They also come with added features such as authentication, software for remote monitoring, and integrated payment gateways.
For now, there are three levels of charging available internationally. Level 1 is 120 volts, which is the lower limit of the charging stations and is widely popular as they can charge both all-electric cars and plug-in hybrids from homes. They are slow, however, and can take up to 12 hours to charge. The Level 2 uses 240 volts and can handle much heavier charging loads. Practically all types of electric vehicles can charge at this level in a few hours. Level 3 uses direct current (DC) and a specific vehicle port to charge the batteries rapidly. These chargers can fill a battery to 85% capacity in less than half an hour.
There are several options to charge electric vehicles, and they can be classified into two broad categories:
Electric vehicle owners can easily charge their cars and scooters with private home chargers designed to run on the 230 volt / 15 amp single phase plugs out of which a maximum of 2.5- 3KW can be drawn. This AC ‘slow’ charging system is the most common type and accounts for about 95% of all EV charging. An EVSE unit supplies a steady AC power to the vehicle’s built-in charger, which converts it to DC to charge the batteries at a rate from 2.5 to 3KW. The system works well with 2, 3, and 4 wheelers for overnight charging. They also act as fast chargers for vehicles with low energy density batteries around 2KWh, such as electric scooters. Four-wheelers with higher capacity batteries in the range of 12KWH or more can be charged within 4 to 5 hours. For faster charging, a higher capacity charging station can be installed at home with a three-phase electrical connection to ramp up the output and shorten the charging times.
Public charging portals outside the home can run at a higher capacity and are also metered by power utilities. They are set up at petrol stations, offices, commercial centres and charging networks and to offer a range of charging options. Typically they have Fast AC charging with output varying from 7.7KW to 22KW. DC rapid charging also becomes a viable option despite its high costs as people can top up their cars with stations offering 50KW or more on highways servicing drivers on long journeys.
Most electric vehicles can be charged at home with a simple charging set up or a charging station. For faster charges on longer commutes, it is possible to tap into a growing network of public chargers places around the cities and highways.
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