What is the difference between alternating current and direct current?
There are 2 types of electricity supply: AC (Alternating Current) & DC (Direct Current). Recharging an Electric Vehicle may be trickier than refuelling a conventional internal combustion engine vehicle.
When it comes to electric mobility, two separate electrical currents can be used to fuel an electric vehicle (EV):
- AC: The power that comes from the grid, i.e., your domestic socket, is always AC (alternating current).
- DC: The energy that is stored in batteries is always DC (direct current).
AC can be efficiently transported over long distances—which is why virtually all of the world’s electricity grids use AC power.
DC can be used for energy storage. We get AC power from the grid and this is converted into DC power so it can be stored in batteries, such as the one used to power an EV.
When we talk about charging an EV, the main difference between AC and DC charging is where the conversion from AC to DC happens. No matter whether an EV uses an AC or DC charging station, the EV’s battery will still only store DC energy.
When you use a DC charging station, the conversion from AC (from the grid) to DC happens within the charging station—allowing DC power to flow directly from the station and into the battery. When using DC fast and ultra-fast charging stations, the conversion happens outside the EV, using a larger converter.
When using an AC charging station, the conversion to DC happens inside the EV via an onboard charger. All EVs come with onboard chargers capable of converting the current before supplying it to the car’s battery. AC chargers are more common in the EV ecosystem as they are comparatively less expensive to produce, install and operate.
On the other hand, DC chargers enable the conversion of current from AC to DC outside the vehicle. DC is then directly fed into the EV, surpassing the need for onboard conversion. These chargers require a lot more power from the grid – nearly 125 A and are much more expensive to produce, install and operate. DC fast chargers are suitable mainly for four-wheelers with large batteries that require instant charging and are found on highways or other locations where an EV might require a quick charge-up in minutes. They are suitable for vehicles travelling long distances or for commercial fleets.
- Potential EV buyers
- Charge-point operators
- Researchers and policymakers
- Residences and workspaces with mandated EV charging
Around 80% of all EV charging is currently done at home. Usually overnight while owners sleep – waking to a fully charged battery the next morning that almost always provides more than enough for most people’s daily travel needs.
Another refresher on AC & DC Charging:
- An AC charger supplies the EV’s onboard charger, which then converts the AC power to DC allowing the battery to charge. The size of the onboard charging device is constrained by space. Due to this limited space, the amount of power they can deliver to the battery is relatively low. Which means that charging is typically slower.
- A DC fast charger bypasses the onboard charging device, supplying power directly to the EV’s battery. The DC charger is external to the car, so it isn’t constrained in size or cost. Meaning that charging is typically much faster.
In India, the electric power supply voltage (AC) is standard 230 V per phase with a frequency of 50 Hz.
Level 1 (on-board charger): It is applicable only for countries with 120 V, 60 Hz grid systems. It does not apply to India as the nominal voltage range of the Indian grid is 220 to 240 V with a frequency of 50 Hz. The advantages of Level 1 chargers are low capital cost, low impact on peak demand charges, and the disadvantage is slow charging. Average Charging Time: 20 hours.
Level 2 (on-board charger): This type of charging has a voltage of 240 V per phase with a current capacity of 80 A (maximum) and power levels ranging from 19.2 to 22 KW. India is currently using this level of charging and it is considered as slow or normal charging and used in home charging and few as public charging. The advantages of Level 2 chargers are faster charging and more energy-efficient compared to level 1 chargers, and the disadvantages are costlier than Level 1 chargers and high impact on peak demand charges. Average Charging Time: 8 hours.
DC Charging (off-board charger): This type of charging is through DC voltage ranging from 50 V to 1500 V DC. This type of charger is also called DC Fast Chargers (DCFC) and is generally preferred to be used as a public charging station. The advantages are high charging power, faster charging compared to Level 1 and 2 chargers, and the disadvantages are more expensive, increase load peaks, the complexity of standards, additional safety and security requirements. Average Charging Time: 0.5 hours.
Superchargers (off-board charger): They are also called TESLA superchargers as it applies only to TESLA EV's manufactured by the company TESLA. The charger has different versions of voltage levels 120 V, 240 V or 400 V or higher. Average Charging Time: 0.33 hours.
Level 1 and Level 2 type of charging is only AC power transfer whereas DC charger and superchargers are only DC-based.
In the future, energy conversion, energy storage, and energy management and dispatch will constitute the core of power supply in urban living. Relying on all public charging stations or home-use charging stations deployed in urban construction, AC power from the power plant or renewable green energy, such as solar power or wind power, can be converted for EV use or home-based energy storage systems for home appliance use. Furthermore, the battery energy stored in the EV can be transmitted back to the power grid. It is foreseeable that charging stations with bi-directional energy conversion ability will create an infrastructure in the future.
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