Time Calculator: Input pack, charger kWh to get time (hours) to charge
EV Charging Basics
EV charging basics
Although you are probably used to how many gallons of gasoline you need to fill your tank, it's a little different with charging up an EV. Mostly, it takes longer to charge a battery pack than top off a gas tank. This page focuses on the basics of charging. Public charging stations are covered on the next few pages.
A quick look at the drawing to the right shows the first basic challenge of home charging an electric vehicle. The diameter of the gasoline pump nozzle is about 10 times that of the household wire.
Add in the fact that the energy density of a modern Lithium-Ion battery is only a fraction of gasoline or diesel fuel, and you can see that wires need to work overtime to match the speed and energy pumped into a gas tank.
The basic unit of electric power used to figure how much energy goes into the battery pack, and how much that energy costs, is the Kilowatt-hour, or kWh for short. One kWh is 1000 Watts.
Watts is Amps times Volts. In most households today, figure on about 15 amps and 110 volts coming out of the wall. These are averages and will vary some...you could have 115 or 120 volts for example.
You may have seen the phrase "Operates on ordinary 110V, 15-amp household current" on a 1500 Watt appliance. The math actually comes to 1650 Watts. With regard to EVs, Level 1 charging is 120 volts at 12 amps for 1440 watts, or 1.44kW.
So, you have a power output from your standard wall plug of about 1500 Watts, or 1.5 Kilowatts. If you want to charge your electric car from a standard wall outlet, you can figure on about 1.5 (1.44) Kilowatts per hour. This is defined as Level 1 charging.
Example Using the Calculators
Using the calculator you can see how long it might take to charge up a Nissan Leaf, or any other battery pack. The Nissan Leaf has a 24 Kilowatt-hour battery pack.
Internet Explorer users: You may have to enable Scripts to use the calculators. Click the yellow bar at the top of the screen, or use tools to enable.
Input to the kWh calculator
Volts = 110
Amps = 12
Time = 1 hour
Output in kWh (Kilowatt hours) = 1.54 kWh
That is how many kilowatts per hour maximum that are coming out of your standard garage wall socket. This is what goes into your EV charger. This is the Charger input to use in the Time calculator.
Input to the Time calculator:
Next, input the kWh from the charger above, and the kWh rating of the battery pack you want to check into the Time calculator:
Battery Pack = 24 kWh
Charger = 1.44 kWh
Time to full charge = 16.7 hours
Wow, almost 17 hours to fill up your Leaf from the wall. This is why manufacturers are installing custom-built higher voltage chargers that can use 220 and 440 volt lines.
220 and 440 Volt Lines
One way to reduce the charge time is to increase the voltage and amperage. Most households have a 220 volt, 30 amp service line for washer and dryer. This drastically reduces charge time. The Level 2 rating for these power lines is 208/240 volts at 32 amps for a total of 6.7/7.7 kW per hour. You can also input these values to the calculators. Volvo is testing a new charging technology in its C-30 EV that can top off the pack in 90 minutes.
To see charge times for over 50 EVs head to the spec section.
Level 3 fast chargers capable of giving Li-ion battery packs a 50-80% charge in from 10 to 30 minutes. These chargers are rated to charge at 480 volts and 400 amps! More on the actual chargers on the next page.
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Kilowatt Calculator: Input volts, amps, and time to get kWh