Slow Home Charging Speeds For EVs: The Reasons

Although on average, the batteries on electric vehicles (EVs) vehicles take about 8 hours to charge from empty to full, the number can range widely, being anywhere from 30 minutes to 12 hours. This depends on the charging speed that your EV allows, the output of your charger and other factors. 

There are a number of things you need to learn about electric vehicle charging to properly and efficiently charge your baby, whether at home or at a public charging station. Read on to learn the basics of EV charging and the most common reasons that could be slowing the home charging speed for your vehicle.

AC Charging vs DC Charging: The Basic

Before we start, it’s essential that you understand the two kinds of electrical power or ‘fuels’ that electric cars consume, since they allow for two types of charging with different charging speed: alternating current (AC) and direct current (DC). While the power coming from the grid is always AC power, batteries like the one in your smartphone or electric vehicle only store power as DC. 

This means that your EV as well as most electronic devices have a converter built into the plug for converting AC power from the grid to DC power, which the batteries can store. With EV charging, the difference between AC charging and DC charging is whether the AC power gets converted inside the car or outside. 

AC Charging: AC charging is the standard and still currently most common charging method for electric vehicles. All electric vehicles have a built-in converter inside, which is called the onboard charger, to convert power from AC to DC  and then feed it into the car’s battery. The conversion happens inside the car with AC charging

DC Charging: Unlike AC charging, the conversion from the grid’s AC power to DC power happens inside the DC charger, thanks to the built-in converter inside the charger itself. This means there is no need for the car’s onboard converter, since the DC charger can convert AC power to DC and directly feed DC power to the car’s battery. 

DC chargers available at public charging stations make for an exciting breakthrough with much faster charging speed. They are bigger and allow for a faster charging experience. This type of charger usually takes about 20 minutes to charge your battery to 50 percent and takes about 75 minutes to restore it to a full charge. 


EV Home Charging

EV home charging speed
For charging your EV at home, now you can use both Level 1 and Level 2 charging. Photo credit:

You can charge your EV at home, at your office or on the go while traveling with domestic sockets in your home or the CEE plugs.

Domestic sockets: All EVs come with a charging cable that allows you to plug into any 120-volt domestic wall socket that you’ll find inside your house. The charging cable and plug for charging with an ordinary wall outlet is often supplied by the car manufacturer for emergency charging on the go. Domestic sockets can also sometimes be found at public charging stations. 

With the appropriate fusing, you can plug your EV into a domestic socket to get charging speed of up to 3.7 kW (230 V, 16 A). This is referred to as Level 1 Charging. If you’re plugging into a domestic socket at an unfamiliar place and thus could not check it beforehand, a maximum charging power of only 2.3 kW (230 V, 10 A) is highly recommended to avoid electrical problems. 

CEE plugs: The more advanced version of the domestic-socket Level 1 charging is a charging cable with a connector for different CEE industrial sockets for higher charging speeds. The CEE plug is available in both the single phase and the triple phase variants:  

  • A single-phase CEE plug is also called a camping plug and is colour coded blue,  with a charging power of up to 3.7 kW (230 V, 16 A)
  • A triple-phase CEE plug is colour coded red and is meant for industrial sockets:
    • large CEE 32 industrial plugs with a maximum charging speed of up to 22 kW (400 V, 32 A)
    • small CEE 16 industrial plugs with a maximum charging speed of up to 11 kW (400 V, 26 A)

Level 2 home charging station: For certain EVs, you can get a Level 2 charging station installed in your own garage for conveniently charging at home, but it will require professional installation and wiring. This is generally not a DIY project. The Level 2 at-home chargers are often available for full-electric cars. 

Level 2 charging stations offer a charging speed of multiple times faster than Level 1 charging,  at 240 volts AC. For any pure-electric vehicle such as the Nissan Leaf, having an at-home charging station for overnight charging is essential. 

Slow Home Charging Speed: Reasons 

If you find Level 1 charging too slow, go for Level 2 for more efficient and faster charging. But note that when you’re charging your EV at Level 2, electrical flows between the grid and your vehicle might be impeded by some potential bottlenecks as follows:

Mismatch between Charger’s Amp Rating and the EV’s Maximum Charging Rate 

The term “Level 2 home charging stations” or “Level 2 chargers” might not have as much consistency as you’d think. Level 2 chargers for charging your EV at home are usually rated in amps, which specify the amount of current a given charger provides at 240 volts. And Level chargers can have varying amp ratings: 12, 16, 20, 24, 32, 40, 48, 64 or 80 amps. 

An electric vehicle’s maximum charging rate is given in kilowatts. This metric is for the vehicle’s onboard charger module, which converts AC to DC. The more power the car can accept, the faster it can charge. 

To allow for the most efficient and thus fastest charging, your charger needs to match your EV’s charging rate. How can you know when they are in different measurements? Just multiply 240 volts by the amps the charger is rated for and you have watts, which can be converted to kilowatts. 

For example, if you have a Level 2 charger rated at 20 amps, then 240 times 20 equals 4,800 watts, or 4.8 kW. This is a good charger for the best selling Nissan Leaf, which has a maximum charging rate of 3.3 kW. In short, the amount of current that a charger provides at 240 volts, when converted to kilowatts, should be higher than the maximum charging rate of your EV. 

Nowadays, roughly 7.2 kW is more common for pure all-electric vehicles, and newer models are even offering 10 kW and above, like the Ford Mustang Mach-E with 10.5 kW and the Volkswagen ID.4 with 11 kW.

You Don’t Have A 240-volt Circuit That Can to Exploit Your EV’s Full Charging Capacity

For most efficient charging and shorter charging time, you need a dedicated circuit that can take full advantage of the maximum charging capacity of your EV and charger. Each 240-volt circuit has a current limit, which is decided by the diameter of its wires and how far these wires have to travel from the fuse box to where you charge your EV. 

Longer cords have more resistance, which slows down charging speed. To meet the current demand of Level 2 EV charging, you need robust enough wiring, which will in turn require larger conduit.

The circuit breaker always needs to provide roughly 25% of headroom. For instance, a Level 2 charger which is rated at 32 amps will require a 40-amp circuit breaker. A 40-amp Level 2 charger will require a 50-amp circuit breaker.