For different categories of electric vehicles (EVs), we need different battery capacities, and so let us see which battery suits which vehicle and how to elongate battery life.
What battery capacities do EVs use
For two-wheelers in India, the battery capacities would be between 1 kWh and 3 kWh. For three-wheelers, it would be from 2.5-8 kWh.
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| EV battery of a four-wheeler -- Photo: Car Magazine. |
In the case of electric rickshaws and small autos, the ideal capacities would be 2.5-3 kWh batteries, and for large autos — that is for those with seven-seater category — it can go up to 5-8 kWh.
For budget four wheelers or passenger cars — that cost Rs 10 lakh (Rs 10,00,000) or less — the battery size will be 15 kWh.
For premium cars, it could be from 30-75 kWh. It can even be higher. In fact, 95 per cent of EVs in India, would be having a battery size of 15 kWh or less.
Voltage requirements for EVs
So far as battery voltages go, globally, two-wheelers and three-wheelers generally use 48 Volts (V) or 72 V.
In the case of medium-to-large cars, 350 V or 380 V may be used. For larger vehicles, the requirement can be 750 V. Let us now look at some aspects of batteries:
For two or three wheelers, the most popular voltage is 48 V and below 60 Volts is considered to be safe. If the voltage threshold is above 60 V, it could be unsafe for two or three wheelers.
Also, when a battery of 48 V is fully charged, it can reach up to 58 V and may require isolation. Also, 60 V is suitable for micro four-wheeler passenger vehicles (having 5-10 kW battery).
Also, it is easy to have a 1 kWh battery at 48 V. But it is not possible to build a 1 kW battery at 350 V.
A 1 kWh battery made at 350 V would require about 100 cells with less than 3 Ah rating and they have to be connected in series.
However, for battery of 10 kW and above, a 350 V could actually be an option.
Such low energy cells cannot be pouch cells or prismatic cells, commonly used in EVs. The only option would be cylindrical cells, which are known to have lower life-cycles.
Same will be the case for battery-sizes of up to 5 kWh. Only when battery size exceeds 10 kWh, 350 V could be a viable option.
In fact, electrical isolation in smaller vehicles can be avoided by usage of 48V batteries.
What is 1C rate of charging?
In the case of low-cost batteries, we do not see the use of 1C rate of charging. The charging rate of a Li Ion cell is termed C-rate of cells.
If you charge at 1C rate, it means fast charging — that is, charging from zero to full in an hour. If it is 0.5C, the charging will take two hours. (double the time taken by 1C).
Conclusion
Low-or-medium cost batteries must not be charged above the rate of IC. IC charging rate for low-cost batteries may take 45 minutes to fully charge. But the fast chargers need a minimum 15 kW battery. In the case of premium vehicles, batteries of higher configuration are needed.
For instance, a 75-kW battery at a rate of 1.5C can charge a premium vehicle in 30 minutes. But remember that only by slow charging can one elongate the EV battery life.
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