Understanding EV Charging Speed

Electric vehicle charging rates are all about how much energy you can transfer to the vehicle at any given moment. There are two measures we see of power: kilowatts (kW) and kilowatt-hours (kWh).

To help understand these terms, a water hose is a good analogy. 

kW is the size of the hose and kWh is the flow through the hose. You can get the same amount of energy (kWh) no matter the size of the hose (kW), but the bigger the hose, the faster you can get that energy. The higher the kW, the faster you can charge, and the lower the kW the slower you can charge. 

To determine the kW (hose size), there are two main factors: How much kW can the charger give and how much kW can the electric vehicle accept

The charger may also be limited by the circuit. If the amperage on a circuit isn’t high enough, then the charger will not be able to reach its potential kW output. For example, if an 11.5 kW charger is on a 60 amp circuit, it can deliver all 11.5 kW. If we put that same charger on a 30 amp circuit, the kW will be approximately cut in half to 5.6 kW. Each charger model will have a recommended amperage for the circuit.

Let’s take a look at some of the more popular charger models we install. Each of these chargers is a level 2 charger. For more information about different charger classifications, see our article on EV Charging Explained.

 

Charger Make/ModelkW Output
Chargepoint Home Flex12.0 kW
JuiceBox 4811.5 kW
SolarEdge (LJ40)9.6 kW
ClipperCreek (HCS-60)11.5 kW
ClipperCreek (HCS-50)9.6 kW
Tesla Wall Connector (only compatible with a Tesla)11.5 kW


 

Now, let’s match those up to some of the vehicles that our customers bought right here in Southern Maryland. These are examples, and different EVs will have different upgrade options.

EV Make/ModelkW Acceptance RateBattery Size
Tesla Model 319.2 kW100 kWh
Ford Mustang Mach-E10.5 kW88 kWh
Chevy Bolt7.7 kW66 kWh
Toyota Rav43.3 kW18.1 kWh
Toyota Prius EV3.3 kW8.8 kWh Nissan
Nissan Leaf6.6 kW62 kWh


So as an example, no matter the charger, a hybrid Toyota Prius will only be able to accept 3.3 kW, but with only an 8.8 kW battery, that would only take 2 hours and 40 minutes (8.8 divided by 3.3) to go from empty to full.

On the other hand, if you purchase a Ford Mustang Mach-E, it has a 10.5 kW acceptance rate. If we use a SolarEdge charger, the transfer of power will be limited to SolarEdge’s 9.6 kW. If we use a Chargepoint Home Flex charger, the transfer of power will be limited to Mach-E’s 10.5 kW.

So what does it matter if we charge at a slower speed? Using the Ford Mustang Mach-E the difference to go from empty to full would be 9.1 hours at 9.6 kW and 8.3 hours at 10.5 kW. While that’s a 15% technical difference, practically, both chargers will charge the vehicle overnight. It is also not likely that you would charge from near 0, so the time to a full charge will always be less, depending on how charged the battery is when you start.

Conclusion

If charge speed is important to you, then the charger you pick will matter. In that case, it would be good to think ahead and plan for future EVs. For example, you may only have a plug-in hybrid right now and speed doesn’t matter, but as technology improves, you may want a faster charger available for your next EV purchase.

Our team is happy to work with you to find the right solution for your needs and concerns.