Electric vehicles, despite all the benefits it can provide, are often brushed aside as it is thought that it takes a long time to charge.
Similarly, we are often asked for how long it takes to charge our electric trucks. It is difficult to answer as charging times for Electric Vehicles are dependent on 3 main factors; Charger Power, Maximum Charging Rate of the EV, and Battery Design.
Let us examine how are charging times estimated.
Charger Power vs Battery Capacity (kW vs kWh)
Firstly, we must understand the difference between power and capacity.
A charger's maximum power output is rated in kilowatts (kW).
A battery's maximum capacity is rated in kilowatt hours (kWh).
We must not confuse between the two. Imagine that you are using a water hose to fill up a tank. The maximum flow of water (liters per hour) will determine how fast it takes to fill the tank to its maximum capacity (liters).
Similarly, the maximum flow of electricity (kilowatts), will determine how fast it takes to fill the battery to its maximum capacity (kilowatt hours).
For example, if an EV has a battery capacity of 200kWh, it will theoretically take
1 hour to charge on a 200kW charger
2 hours to charge on a 100kW charger
4 hours to charge on a 50kW charger
Bottlenecks
EV charging speeds are limited by the high-power cables connected to the vehicle's battery. The higher the charge power, the larger the diameter of the cables. This is to allow effective heat dissipation when a high current is applied through the cables. If a vehicle is only rated to accept 100kW of charging power, a 200kW charger will limit its output to match. This means that the charger is not 100% utilised.
It is important to understand the maximum charging rate that the EV can accept before your purchase. This understanding will also allow you to choose the best charger for your needs. It will also prevent you from spending too much on your EV charging stations.
Battery Design
Battery charging times are often quoted as 'theoretical' as we can only estimate the power on paper using the methods that I described above.
In reality, the battery management system (BMS) in EVs monitor more than 100 parameters of the battery pack to ensure that the battery does not catch fire. These parameters include battery cell temperature, cell voltage, cable temperature etc.
If any one of these parameters have been deemed by the BMS to pose a risk, the BMS communicates it to the charger to reduce the charging power to keep things safe. Therefore, an EV usually deviates a few minutes from its theoretical charging times.
EV charging is wonderfully complex and a marvel of modern engineering. However, the concepts it is based on are simple and elegant. To learn more and dive deeper into the technology, speak to any one of us at EcoSwift today!
-Ryan Woon, Director, EcoSwift Pte Ltd
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