How to Calculate Charging Times for your Electric Car
About Charging Times and Electric Vehicles
How long it takes to charge your electric car depends battery size, maximum charge capability and the amount of energy supplied.
Battery capacity can vary from 9 kWh to over 91 kWh, depending on make and model. Technology is changing rapidly, in terms of capacity and speed of charging, but calculating how long it takes to charge your electric car is easy. Let’s have a look.
First, you are limited by the capacity of the equipment supplying your car and the car itself. EVs actually have a charger built-in. Either can create a bottle-neck for the energy flowing to your batteries.
In the case of charging at home, using alternating current (AC), the charger is built-in the car. It can be referred to as an “on-board charger.” The unit outside of your car, which provides energy in a regulated and safe manner, is energy supply equipment. These are usually designated Level 1 and 2 chargers.
Home energy is AC, but batteries are DC. The car will take the AC, and switch the current to direct current (DC) for storage in your batteries, using the on-board charger.
Where as, when using a public fast charger with DC, the charger is built into the supply equipment, or the large gas pump-looking thing.
Here, we are putting DC in to DC. But, to regulate the energy safely, the supply equipment outside of the car manages the flow, not the on-board charger.
So, between the equipment that we plug in to our car and the on-board charger, we need to find which one is restrictive.
Both supply equipment outside the car, or the car itself, will be a rated in kilowatts (kW).
Now, Find the Bottleneck!
For AC home, or level 1 or 2 charging, the number of kilowatts is lower. For DC fast chargers and the car’s ability to handle DC charging, the number of kilowatts is higher, by often many times.
A typical home charger, such as the Grizzl-E Smart, has a max rating of 10 kW. Where as a car might have an on-board charger of 6.6 kW. In this case, the most energy available for charging is 6.6 kW. The car is the bottleneck.
The same principle applies for DC charging. Whichever kW rating is lower, that’s the bottleneck. A car might have a max 130 kW DC capacity, and you may find a DC fast charger with only 50 kW of power. The charger outside of the car is the bottleneck.
It is a simple formula, just take the battery capacity and divide it by the amount of energy being allowed to flow to the batteries.
Batteries are defined in kilowatt hours (kWh) so you don’t have to convert energy units and your calculation will give you a time-based result.
Divide battery capacity in kilowatt-hours by charge power in kilowatts:
Battery Capacity (kWh) / Charge Power (kW)
Let’s try it.
Say you have a 2022 Hyundai Ioniq 5 with the long range 77kWh battery and you are using the Gizzl-E Smart from EasyEV Inc, with 10kW, 40A.
Your Ioniq 5’s on-board charger will allow 19kW of AC power to charge. The 19kW is more than the Grizzl-E can supply, so we use the 10kW in the calculation, because it’s the maximum Charge Power available (the supply equipment is the bottleneck here).
The quick math:
77 kWh / 10 kW = 7.7 hours to charge from 0 to 100%
The above formula will give you a very-literal calculation, but doesn’t account for inefficiencies of the charging process. This can be resistance in the electrical hardware, such as wire, connectors, and supply equipment or even weather.
To factor that in, you reduce the Charge Power by multiplying it by .9, or 90% of it’s maximum power capability.
Battery Capacity (kWh) / Charge Power (kW) x 0.9 or 90%.
Now it’s more realistic. Keep in mind, this will give you the time to charge, from 0 to 100% capacity.
What if there is energy left in the “tank?”
Let’s again say you have a 2022 Hyundai Ioniq 5 with the long range 77kWh battery and you are using the Gizzl-E Smart from EasyEV Inc, with 10kW, 40A.
Every battery has a 100% capacity. Subtract 100% from the current Battery Capacity your currently has. Then, you multiply it by the max battery capacity of your electric car.
Now, let’s solve it, to find the remaining amount:
100 – Percentage of Remaining Battery Capacity.
So, 100 is 100%. Then, you just subtract what you see on your car’s dashboard or app.
If your car has 27% of Remaining Battery Capacity, then minus that from 100.
100 – 27 = 73. This is how much room you have in the “tank,” as a percentage. We need to put this in to a decimal number, for our formula: 73/100 = .73.
Here it is:
Battery Capacity (kWh) (Remaining %) / Charge Power (kW) x 0.9
Battery Capacity 77kWh divided by Charge Power 10kW x 0.9
Result: 77 / 10 (0.9) = 8.56 hours from 0 to 100%
Let’s do it again, and say you have 27% Battery Capacity Remaining.
100-27 = 73,
77(.73) / 10 (0.9) = 6.25 hours to charge from 27% to 100%
Your Onboard Charger as the Bottleneck
Use the lower number between the onboard charger and supply equipment.
If your car charger is rated at 6.6kW and the Grizzl-E Smart is 10kW, use 6.6kW. For this, let’s use an older Nissan Leaf’s Battery Capacity of 30kWh.
30 / 6.6 (0.9) = 5.05 hours from 0 to 100%
And if it has 68% Battery Capacity Remaining, then 100 – 68 = 32. Don’t forget to turn it in to a decimal, 32 / 100 = .32.
30(.32) / 6.6 (0.9) = 1.62 hours from 68% to 100%.
In a Perfect World and Ideal Conditions
Simple, once you get the hang of it. We should also say, these are approximate calculations or estimates. More often than not, you will have efficiency loss and other factors to make it charge quicker or slower. Cold temperatures can affect the efficiency and not all charging supply equipment is made equally.