How Station Amperage and kW Affect EV Charging Times

Electric vehicles (EVs) are still a relatively new technology, and many people find them somewhat confusing, especially when it comes to charging times. If you arrive at a public EV charger and see an unexpectantly long estimated charging time, you might think the charger is faulty. However, there’s more to it than meets the eye.

In this blog post, we’ll clarify the factors affecting EV charging times.

How does charging an EV battery work?

First, let’s explore how EV batteries get charged.

Both plug-in hybrid electric vehicles (PHEV) and battery electric vehicles (BEV) have built-in, onboard chargers. When using Level 1 (L1) and Level 2 (L2) charging stations, these stations supply alternating current (AC) power into the EV’s onboard charger. The onboard charger then converts the AC to direct current (DC) power, which charges EV’s battery.

Charging an EV battery is similar to charging your laptop. When you plug your laptop into a wall outlet, the outlet supplies AC power to the laptop’s charger (the box that is part of its cord), which converts it to DC power and charges the laptop’s battery. When you use a DC fast charger (DCFC), the charging station handles the AC to DC conversion using its power electronics. The station supplies DC power directly to your EV, bypassing the onboard charger.

Charging an EV with AC and DC power.

Because the converter electronics in a DCFC are larger and more powerful than those in an EV, DCFC charging is so much faster than Level 1 and Level 2 charging. With Level 1 and Level 2, the AC to DC conversion happens inside the EVs onboard charger, while with DCFC, the conversion occurs in the station itself. Your vehicle’s onboard charger isn’t involved when using a DCFC.

Now that we’ve covered how an EV's battery is charged, let’s discuss how voltage, amperage, and kilowatts work together to affect charging speed.

Volts, amps, kilowatts, and your EV

The speed at which your EV battery charges depends on the power capacity of your EV's built-in charger (how many kilowatts it can draw) and the power supply of the EV charging unit (its voltage and amperage).

Think of volts and voltage, amps and amperage, and power and kilowatts like water flowing through a hose:

Voltage (V) is like water pressure .
Amperage (amp) is like water flow.
Pressure times flow is equivalent to electrical power, measured in kilowatts (kW).

Together, volts and amps deliver kW to your onboard EV charger.

Each charging unit has an amperage rating, indicating the maximum amount of electrical current it can deliver to your EV. For example, a charging unit with a 30 amp rating can deliver up to 30 amps.

Level 2 charging amperages

Level 2 charging units in North America run on 240 volts, the same as your oven or clothes dryer, providing a steady pressure of 240 volts of electricity. These stations come with various amperage ratings to meet the power needs of different EVs. For instance, the Blink Series 7 Level 2 Charging Station can deliver up to 80 amps of power to your EV. (Note that residential homes typically have a 240V service, while commercial buildings have 208V, and Blink’s Level 2 charging stations are compatible with both.)

However, a higher amperage rating on a Level 2 EV charging station doesn’t necessarily mean quicker charging.

This is because your EV battery can only safely handle a certain number of kilowatts. Each EV has a kilowatt rating that indicates how much power the battery can accept. Generally, EVs have two power ratings: a lower AC power and a higher DC power. For example, if your EV can charge up to 7.2 kW, it will only accept up to 7.2 kW of electrical power.

To determine how much power will flow to your EV's battery, find the lesser value between your EV onboard charger power and the maximum charging station power. You can calculate the maximum charging station power using the following formulas:

Volts x Amps = Power (in Watts)
Watts ÷ 100 = kW

Let’s see how this works with some examples.

Example 1

A 240 V Level 2 charging station with a 30 amp rating will deliver 7.2 kW of electricity to your EV battery.

240 V x 30 A = 7,200 W
7,200 W ÷ 1,000 = 7.2 kW

This Level 2 charging station can provide up to 7.2 kW.

Example 2

If we replace the 30 amp charging station with an 80 amp Level 2 station, the result changes:

240 V x 80 A = 19,200 W
19,200 W ÷ 1,000 = 19.2 kW

This Level 2 charging station can supply up to 19.2 kW of power.

How the EV maximum charging rate affects charging

Now let’s discuss your EV's maximum charging rate, which is the highest amount of power the battery can safely accept, regardless of the power supplied by the EV charging station.

Suppose you have an EV with a 7.2 kW rating. This means if you use the charging station from Example 1, your EV can accept the full 7.2 kW of power that the charging station can supply.

However, if you plug this same EV into the charging station from Example 2, it can still only accept a maximum of 7.2 kW of power. This is because the EVs onboard charger will never accept more than 7.2 kW of power. No matter how much power the charging station provides, the onboard charger can only handle its maximum rating of 7.2 kW.

Note that DC fast chargers (DCFCs), like the Blink Series 9 30kW DCFC, Blink 60kW - 360kW DCFC, and Blink Hypercharger 400kW DCFC bypass the vehicle’s onboard charger and charge the battery differently. Therefore, these rating are not applicable to DCFCs.

Load management features can affect charging time

Another factor that can affect charging times is load management (including demand response).

In brief, multiple charging stations can share an electrical circuit by splitting the available power between them, which can decrease the available amperage and, consequently, the charging power.

For example, if you have three 30 amp Level 2 charging stations sharing a 30 amp electrical circuit, the available 30 amps would be split between the stations in use. If one station is in use, it gets the full 30 amps of available power. If another vehicle plugs into another charger on that circuit, each charging stations would receive 15 amps of power.

Using our formula, we can see how this affects the amount of kW delivered to the EV:

240V x 15A = 3,600W
3,600W ÷ 1,000 = 3.6kW

In this scenario, due to local load management, the charging stations in use would only be able to supply 3.6kW to each vehicle, which would naturally increase the charging time.

If a third vehicle plugs into the same 30 amp circuit, each station in use would only receive 10 amps of power and be able to deliver only 2.4 kW to the EVs.

So how long does it take to charge an EV?

No matter the amperage of a charging unit, your EV will only draw as much power as the battery can safely handle. If the charging station uses local load management, this can decrease the power each station received and reduce the kW it can deliver to the EV's onboard charger.

So, when you encounter a public Level 2 charger and the charging time seems unusually long, it is likely due to either your EV's maximum charge rate or the charging station being affected by local load management.

Blink members can use the Blink Mobile App to view their EV's battery percentage, current charging speed, total energy delivered, charging session duration, and the estimated cost to reach full charge.

Ready to install or upgrade a Level 2 charging station or a DC fast charger? Contact Blink Charging today to speak with an EV charging expert.