EV Charging Stations – Beginner’s Guide
Updated: Jan 7, 2020
The first topic, and perhaps one of the most important for The Electron is Electric Vehicle Charging Stations. There is limited understanding in the Indian market about what are these types of EV charging stations and what is the basic underlying principle for the same.
But before we talk about EV charging stations, we need to understand the charging mechanism of EVs. So EVs run on electric energy which is stored in their batteries (which also makes EVs 20-30% heavier in weight than conventional petrol/diesel vehicles). These batteries provide direct current (DC) power to the electric motor - that’s what drives the car. Now the interesting thing to note is that these batteries charge via DC, but all the electricity that is provided to our residential or commercial locations is in the form of alternating current (AC). Solution? We need to change AC into DC before we can charge the batteries. We also need to understand that while we change AC power from the mains supply into DC power, it needs to be at a specific voltage range as per battery specifications, otherwise we might harm the batteries. This is where the on-board charger of the car comes in the picture, On-board charger’s main function is to convert AC power into DC power through a process called rectification, before delivering it to the batteries at the right voltage.
Now you might be thinking - if we have an on-board charger converting AC to DC and delivering power at the right voltage, what is the point of an external charging station? Hold that thought, we will come back to it later.
Now when we talk about EV chargers, there are 2 types of Chargers based on their current:
1. AC Chargers (Level I and II)
2. DC Chargers (Level III)
These chargers as their name suggest take power input as AC and deliver it directly to on-board charger (in AC itself). These chargers have different charging speeds, however, an EV is never charged at the rate of faster than its on-board charger will allow. For e.g., if we connect a 7 kW AC charger to an e-Verito (D4 variant), whose on-board charger have a rating of 2.2 kW, its batteries will be charged at 2.2kW power and not 7 kW, due to limitation of its on-board charger. In this case, car would be fully charged (from 0) in roughly 18.55 kWh (energy capacity of the e-Verito battery) / 2.2 kW = 8.4 hrs. AC chargers usually have a maximum power output < 43 kW.
DC chargers deliver DC power directly to the car, hence there is no use of the on-board charger in the car, which is by-passed. These chargers have in-built heavy-duty rectifiers that convert AC to DC before delivering to the car battery, this is the reason why DC chargers are large in size. DC chargers usually have power output starting from 10 kW and go all the way to 300-400 kW and are a faster means to charge EVs. If we consider the example of e-Verito (D4 variant) connected to a 10 kW DC charger, it would take 18.55 KWh / 10 kW = 1.85 hrs to fully charge from 0%.
Coming back to the earlier question - Why do we need an external charging unit? The answer lies in the protocol that helps keep EV safe while charging. When a charger is connected to EV, it ensures that max. current provided does not exceed the current an EV can receive. It also ensures that current is not flowing when connector is not connected or can detect hardware faults, electrical fault or fire.
In Our Next Article we will dig deeper into what are EV charging connectors?
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