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How long does it take to fill up an electric car at your home?

July 15, 2021

Home charging is the most common way for new energy electric vehicles charging, usually using AC charger, which is what we call slow charging.

There is a simple formula for the charging time of electric vehicles.

Charging Time = Battery Capacity / Charging Power

According to this formula we can roughly calculate how long it takes to get a full charge.

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In addition to battery capacity and charging power, which are two factors directly related to charging time, balanced charging and ambient temperature are also common factors that affect charging time.

1、Battery Capacity

Battery capacity is one of the important indicators to measure the performance of electric vehicles.

Simply put, the larger the battery capacity, the higher the pure electric range of the car, and the longer the charging time required; the smaller the battery capacity, the lower the pure electric range of the car, and the shorter the charging time required.

The battery capacity of battery electric vehicles usually ranges from 30kWh to 100kWh.

For example.

The Tesla Model X long range version has a battery capacity of 100kWh and a range of 575km.

The battery capacity of plug-in hybrid electric vehicles is relatively small, usually between 10kWh and 20kWh, so its pure electric range is also low, usually between 50km and 100km.

For the same model, the higher the battery capacity, the higher the range will be when the vehicle weight and motor power are basically equal.

2、Charging power

Charging power is another important indicator that determines charging time. The higher the charging power of the same car, the shorter the charging time required.

The actual charging power of electric vehicle has two influencing factors: the maximum power of EV charger and the maximum power of AC charging of electric vehicle, and the actual charging power is taken as the smaller of the two.

A. Maximum power of EV charger

The common AC EV charger power is 3.5kW and 7kW. The maximum charging current of 3.5kW EV charger is 16A and the maximum charging current of 7kW EV charger is 32A.

B. Electric vehicle AC charging maximum power

The maximum power limit of AC charging of electric vehicles is mainly reflected in three aspects.

① AC Charging Interface

The specifications of the AC charging interface are usually available at the EV interface label.

For pure electric vehicles, most charging ports are 32A, so that the charging power can reach 7kW. There is also a part of pure electric car charging interface is 16A.

Due to the small battery capacity, most of the plug-in hybrid cars are equipped with a 16A AC charging interface, charging a maximum power of about 3.5kW. A few models are equipped with a 32A AC charging interface, with a maximum charging power of 7kW.

② Power limit of vehicle charger

When using AC EV charger to charge electric vehicles, the main role is power supply and protection. The component that does the power conversion to convert AC power to DC power for battery charging is the on-board charger. The power limit of the on-board charger will directly affect the charging time.

For safety and other reasons, some vehicles can be set through the central control or cell phone APP charging current limit. For example, Tesla, the current limit can be set through the central control. When the charging post can provide a maximum current of 32A, but the charging current is set at 16A, then it will charge at 16A. In essence, the power setting also sets the power limit of the on-board charger.

In summary, for the above-mentioned Tesla Model X Long Range Edition 100kWh EV, the main component that affects charging time is the AC charger as the on-board charger supports a maximum 32A charging current.

Time required to fully charge using a 3.5kW EV charger:

Charging time = 100kWh/3.5kW = 28.6 hours

Time to full charge using a 7kW EV charger.

Charging time = 100kWh/7kW = 14.3 hours

With double the charging power, the charging time will be reduced to half of the original time.

3、Balanced charging

Equalization charging means that after the general charging is completed and continues for a period of time, the high-voltage battery pack management system performs a balancing operation on the individual lithium battery cells. Equalization charging can make the voltage of each battery cell reach basically the same, so as to ensure the overall performance of the high-voltage battery pack. The general vehicle equalization charging time may be around 2 hours.

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4、Ambient temperature

The power battery of new energy electric vehicles is ternary lithium battery or lithium iron phosphate battery, when the temperature is low, the movement of lithium ions inside the battery decreases, the chemical reaction slows down, the battery is less energetic, which will lead to longer charging time. Some vehicles will heat the battery to a certain temperature before charging, which will also extend the charging time of the battery.

As can be seen above, the charging time derived from the battery capacity/charging power is basically comparable to the actual charging time, where the charging power is the lesser of the AC charger power or the on-board charger power. Considering the balanced charging and charging environment temperature, the deviation is basically within 2 hours.

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