Updated: Apr 2, 2020
WHAT ARE CHARGERS?
A battery charger, or recharger is a device used to put energy into a secondary cell or rechargeable battery by forcing an electric current through it. The charging protocol (how much voltage or current for how long, and what to do when charging is complete, for instance) depends on the size and type of the battery being charged.
Electric vehicles ideally need high-rate chargers. For public access, installation of such chargers and the distribution support for them is an issue in the proposed adoption of electric cars.
C-Rate of Charging and Discharging
Charge and discharge rates of a battery are governed by C-rates. The capacity of a battery is commonly rated at 1C, meaning that a fully charged battery rated at 1Ah should provide 1A for one hour. The same battery discharging at 0.5C should provide 500mA for two hours, and at 2C it delivers 2A for 30 minutes. Losses at fast discharges reduce the discharge time and these losses also affect charge times. A C-rate of 1C is also known as a one-hour discharge; 0.5C or C/2 is a two-hour discharge and 0.2C or C/5 is a 5-hour discharge. Some high-performance batteries can be charged and discharged above 1C with moderate stress. Table 1 illustrates typical times at various C-rates.
1. Constant Voltage
2. Constant Current
3. Constant Voltage and Constant Current (CVCC)
The charger has three key functions:-
1) Getting the charge into the battery. (Charging)
2) Optimizing the charging rate. (Stabilizing)
3) Knowing when to stop. (Terminating)
HOW DOES A BATTERY CHARGER WORK?
A battery charger is basically a DC power supply source. Here a transformer is used to step down the AC mains input voltage to the required level as per the rating of the transformer.
This transformer is always a high power type and is able to produce a high current output as required by most lead-acid batteries.
A bridge rectifier configuration is used to rectify the low voltage AC into DC and is further smoothed by a high value electrolytic capacitor.
This DC is fed to an electronic circuit which regulates the voltage into a constant level and is applied to the battery under charge, where the energy is stored through an internal process of chemical reaction.
In automatic battery chargers a voltage sensor circuit is incorporated to sense the voltage of the battery under charge. The charger is automatically switched OFF when the battery voltage reaches the required optimum level.
Types of EV Chargers
There are three main types of EV charging – rapid, fast, and slow. These represent the power outputs, and therefore charging speeds, available to charge an EV. Power is measured in kilowatts (kW).
Rapid Chargers:- are the fastest way to charge an EV, and predominantly cover DC charging. This can be split into two categories – ultra-rapid and rapid. Ultra-rapid points can charge at 100+ kW – often 150 kW – and up to 350 kW, and are DC only. Conventional rapid points make up the majority of the UK’s rapid charging infrastructure and charge at 50 kW DC, with 43 kW AC rapid charging often also available.
Fast Chargers:- include those which provide power from 7 kW to 22 kW, which typically fully charge an EV in 3-4 hours. The most common public charge point found in the UK is a 7 kW untethered Type 2 inlet, though tethered connectors are available too for both Type 1 and type2.
Slow Units:- (up to 3 kW) are best used for overnight charging and usually take between 6 and 12 hours for a pure-EV, or 2-4 hours for a PHEV. EVs charge on slow devices using a cable which connects the vehicle to a 3-pin or Type 2 socket.
Electric Vehicle Battery Chargers
Electric vehicle battery chargers (ECS) come in a variety of brands and characteristics. These chargers vary from 1 kW to 7.5 kW maximum charge rate. Some use algorithm charge curves, others use constant voltage, constant current. Some are programmable by the end user through a CAN port, some have dials for maximum voltage and amperage, some are preset to specified battery pack voltage, amp-hour and chemistry. Prices range from $400 to $4500.
A 10 amp-hour battery could take 15 hours to reach a fully charged state from a fully discharged condition with a 1 amp charger as it would require roughly 1.5 times the battery's capacity. Rapid charging results in even faster recharge times and is limited only by available AC power, battery type, and the type of charging system.
Onboard EV chargers (change AC power to DC power to recharge the EV's pack) can be:
Isolated: they make no physical connection between the A/C electrical mains and the batteries being charged. These typically employ some form of inductive connection between the grid and a charging vehicle. Some isolated chargers may be used in parallel. This allows for an increased charge current and reduced charging times. The battery has a maximum current rating that cannot be exceeded.
Non-isolated: the battery charger has a direct electrical connection to the A/C outlet's wiring. Non-isolated chargers cannot be used in parallel.
Power Factor Correction (PFC) chargers can more closely approach the maximum current the plug can deliver, shortening charging time.
Now, that we are shifting our everyday commute to EV’s, best battery charging technology and how can we charge a battery in the fastest way possible is a big area of research. Companies in the world like Tesla, BMW, Audi, Panasonic and other Indian counterparts like Ion-Energy are working hard to make charging for EV’s both economically feasible and reliable for day to day usage. Chargers are an essential part of the EV ecosystem which cannot be simply ignored and huge transformation in this technology might lead to a better future of EV’s in India and around the World.