EV charging time: Understanding the "weakest link"

A common question when charging an EV at home is, “How long will it take to charge my vehicle?” The answer depends on more than just the charger. Charging speed is limited by the “weakest link” in the charging chain.

This article explains what limits charging speed, how to estimate charging time, and what to check if your vehicle is charging slower than expected when using a Generac Level 2 Plus EV charger.

Environment

This article applies to:

• Generac Level 2 Plus EV chargers

Issue or question

• You want to estimate how long it will take to charge your EV.
• Your EV is charging slower than expected, or the charger is delivering less power than expected.

Cause

Charging power is limited by the lowest (weakest) capacity among these three items:

• Your home electrical circuit (breaker size, wiring, and how much power is available for EV charging).
• Your charger’s configured limit (the maximum current set during installation and any power limit set in the Generac EV Charging app).
• Your vehicle’s onboard charger (the maximum AC charging power your vehicle will accept).

Note: EV charging is a continuous load. For safety, the installed circuit and charger current limit should follow applicable electrical codes. Electrical changes should be performed by a qualified electrician.

Procedure

Step 1: Estimate the power your vehicle can actually receive

To estimate charging time, start by estimating the actual charging power you can achieve. In most cases, actual power is limited to the lowest value from your circuit limit, charger limit, or vehicle limit.

If you are not sure what your charger is limited to, see How to adjust the Level 2 Plus charging current (includes how the limit is set during installation and how to adjust the limit in the app).

Step 2: Estimate how much energy you need to add

Your vehicle battery capacity is usually shown in kWh (kilowatt-hours). The energy you need to add depends on how much charge you want to add (for example, from 20% to 80%). Many vehicles and vehicle apps also estimate how many kWh are needed to reach your target.

Step 3: Estimate charging time

A simple estimate is:

Charging time (hours) ≈ Energy to add (kWh) ÷ Charging power (kW)

Example: If you need to add 30 kWh and your actual charging power is about 7 kW, then charging time is about 4 to 5 hours.

Note: Charging power commonly tapers down as the battery gets closer to full. It may also reduce in cold or hot conditions. Because of that, real-world charging times can vary.

What to check if charging is slower than expected

Use the checks below to identify the most common causes of reduced charging power:

See also

• Generac Level 2 Plus EV Charger FAQ
• Quick start guide: Level 2 Plus
• First time setting up and using your charger
• How to update your charger’s software with the Generac EV Charging app
• How to restore your Generac EV charger to factory settings
• Can I use a portable generator to charge my electric vehicle (EV)?