Calculating EV Charging Times

When installing an EV charging point, it’s important to understand how much charge a user can draw in a given time period.

For example, when installing chargepoints at a shopping centre, a faster rate of charge is more important then when installing a home chargepoint to be used over night.

In this article, we’ve set out the factors that affect charging speed and how to calculate charging times.

Charging Speed Factors

There are three factors that affect charging speed.

  • Charge Point Rating – The higher the power rating of a chargepoint, the faster it will charge a vehicle.
  • Vehicle Charging Rate – All EV’s have a maximum charge rate. An EV with a max charge rate of 7kW will not charge faster, even if plugged into a 22kW charger.
  • Temperature – EV batteries can take longer to charge at lower temperatures.

Calculating Charging Times

The first calculation to make is how long it will take to recharge an empty battery.

This is known simply as the empty-to-full charging time.

Charging time = Battery Capacity (kW) / Chargepoint Rating (kW)

In normal use, EV drivers will never have a completely empty battery. We can take the formula above one step further by working out how long it will take to charge a partially empty battery.

Charging time = (1 -( percentage charged / 100)) * Battery Capacity (kW) / Chargepoint Rating (kW)

Don’t worry if this formula seems confusing.

To help make things easy for you, we’ve created an interactive calculator below. Feel free to bookmark this page and return to use the calculator whenever you need.

Top up Charging

When charging at a destination, many EV drivers are looking to “top-up” their battery instead of receive a full charge. This will give them confidence that they will always have the range they need. Because of this, most locations such as supermarkets and leisure parks use fast chargers which are ideal for this application.

We’ve set out the calculation for additional miles of range below. It’s slightly more complicated as it requires you know the efficiency of the vehicle.

As a guide, the most efficient EVs currently available are around 240 Wh/mile. The least efficient use around 420 Wh/mile.

Added Range = Time in hours * Chargepoint power * 1000 / Efficiency in Wh/mile

As before, we’ve created an easy to use calculator below.

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