“Slow charge” and “fast charge”, how do choose?

Many EV owners will automatically classify it as “slow charge” and “fast charge“.

So, is this really the case?

Most electric vehicles are generally equipped with two charging ports: one seven-hole and one nine-hole.

Compared with oil vehicles, which have only one fuel-filling port, electric vehicles are often equipped with two charging interfaces, namely AC charging interface (seven holes) and DC charging interface (nine holes).

The reason for this is that there are two ways to charge electric vehicles.

Level 2 Charging

▲The alternating current is converted into direct current by the car charger and then charged to the power battery.

EV charging is the process of charging electricity from the grid into a power battery. However, the electricity of the grid is alternating current, and the power battery uses direct current.

Therefore, converting AC to DC to charge EVs.

The power module in the DC charger and the onboard charger in the car are the devices to achieve this transformation.

DC Fast Charging

Alternating current is converted into direct current through the power module in the DC charger to charge the power battery directly

slow charge VS fast charge

In general, the higher the charging power, the larger the volume of the onboard charger /power module will be. Therefore, limited by the interior space and vehicle cost, and other issues, the power of the onboard charger is relatively small, and the power demand for the AC charger does not need to be too large.

It usually takes 6 to 8 hours to fill, which naturally becomes synonymous with “slow charge”.

The DC charger, which is mostly built in public places, has small restrictions on capacitance and volume. So the power module and charging power are larger, so we call it “fast charge”.

But does the AC charger fill more slowly than the DC charger? That’s not the case. The charging power determines the charging speed.

For example, Bluesky’s wall-mounted DC charger CDZ-VT Series with a power of 20kW, while the floor-type AC charger CDZ-B Series has a maximum power of 44kW.

Of course, the use of a high-power AC charger also requires the vehicle itself to have higher specifications of onboard chargers.

For civil electricity, the voltage is mostly single-phase 220V and three-phase 380V. The recommended value of GB/T standard current is generally 16A/32A/63A. At the same time, in single-phase charging, the current shall not exceed 32A.

Therefore, the maximum power of single-phase charging is about 7kW (220V×32A), while the minimum power of three-phase charging is about 11kW (220V×16A×3).

If the onboard charger only supports single-phase electricity, even if you use the 11kW EV charger, it can only obtain about 3kW charging power (220V×16A). It’s not faster than a 7kW charger.

Therefore, it is necessary for EV owners to confirm whether their cars have power before purchasing AC chargers.

Combine fast and slow charge

So, in the charging process, how should we choose? It is best to combine ‘’fast charge’’ and ‘’slow charge’’.

Many owners may have such a feeling: the electricity from the slow charge is more “durable” than the electricity from the fast charge. In fact, it is.

When charging, the battery will produce a polarization reaction. It’s like the foam that comes from pouring beer into a glass. The faster you pour, the more foam you’ll get, and the less beer you’ll actually pour into the glass.

Therefore, compared with “slow charging”, the “foam” generated by “fast charging” will relatively increase. The amount of electricity actually charged is reduced.

In the case of the same display is 100%, and the battery life of “fast charge” is shorter than that of “slow charge”, about 15%.

Combine fast and slow charge

So if you do not pursue the charging time, it is better to use slow charging.

At the same time, try to keep the SOC between 20% and 90% to avoid overcharging and excessive electricity consumption.

And the lithium iron phosphate battery should be charged at least once a week if time permits, in order to correct the SOC value.

Now, will you simply think that AC is a slow charge and DC is a fast charge?

Further Reading

  1. What is Residual Current Device (RCD) in EV Chargers?
  2. What is EV Charging Load Balancing
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