A clear, beginner‑friendly guide to understanding EV charging speeds — including kW, amps, voltage, AC vs DC, outlet types and how your EV’s onboard charger determines your maximum AC charging speed.
Key Takeaways
- kW (kilowatts) measure charging speed — higher kW = faster charging.
- Amps + voltage determine how much power your charger can deliver.
- Your EV’s onboard charger sets the maximum AC charging speed.
- DC fast charging bypasses the onboard charger for much faster speeds.
- Most Australian homes support up to 7.2kW AC charging with a 32A circuit.
Related EV guides: Installation Costs for EV Charging Outlets • 7.2kW vs 3.3kW • Charging at Home 101
EV charging can feel confusing at first — kW, amps, volts, AC, DC, onboard chargers and outlet types all affect how fast your EV charges. The good news - once you understand a few basics, charging becomes simple and predictable.
This guide breaks everything down in clear, everyday language so you can choose the right charger and understand exactly how fast your EV can charge at home and on the road.
To make these concepts easier to understand, here’s a simple visual that shows how voltage, amps, and kilowatts work together — and how they translate into real charging speeds for different outlets and chargers.
Now let’s break down each factor so you can see how these numbers apply in real life.
What Does kW Mean?
(Charging Speed)
Kilowatts (kW) measure how fast energy flows into your EV battery.
Higher kW = faster charging.
Formula: Power (kW) = Voltage × Amps ÷ 1000
Real Examples (Australian Power)
- 10A × 240V = 2.4kW
- 15A × 240V = 3.6kW
- 32A × 240V = 7.6kW (rounded to 7.2kW for EV charging)
These numbers directly translate to charging speed. For example, a 7.2 kW charger adds roughly 30–40 km of range per hour, depending on the EV.
What Is Amperage (Amps)?
Amps measure how much electrical current flows through the charger.
Higher amps = more power delivered to your EV.
Common Australian Outlets
- 10A: Standard household outlet (slow charging)
- 15A: Heavy‑duty outlet with larger earth pin (moderate charging)
-
32A: High‑power outlet for fast AC charging. Two types:
-
32A (3‑pin, single‑phase) 240V × 32A ≈ 7.2 kW → around 30–40 km/hr
-
32A (5‑pin, three‑phase) 415V × 32A ≈ 22 kW → around 100–120 km/hr (Three‑phase outlets always use 5 pins. This is the type used for faster AC charging when your EV supports 11 kW or 22 kW onboard charging.)
-
Why amps matter
A 32A outlet can deliver over 3× more power than a 10A outlet. This is why upgrading from a trickle (granny) charger to a 32A setup dramatically reduces charging time.
What Is Voltage?
Voltage is the electrical “pressure” that pushes current into your EV.
Australian Voltage
- Single‑phase: 230–240V
- Three‑phase: 400V (line‑to‑line)
Why this matters
Three‑phase power allows much faster AC charging:
-
Single‑phase max: ~7.2 kW
-
Three‑phase max: 11–22 kW (depending on the EV)
Level 2 AC charging comes in two types: single‑phase (up to ~7.2 kW) and three‑phase (up to 22 kW). Most Australian homes are single‑phase, which is why 7.2 kW is the common home charging limit. Three‑phase is typically found in newer builds, commercial sites, workshops and some rural properties, allowing much faster AC charging when paired with an EV that supports 11 kW or 22 kW onboard charging.
Your EV’s Onboard Charger: The Real Speed Limit
The onboard charger is a built‑in component that converts AC power into DC to store in the battery. It determines the maximum AC charging speed your EV can accept — no matter how powerful the charger is.
Common Onboard Charger Ratings
- 7kW: Most EVs in Australia
- 11kW: Premium and European EVs
- 22kW: Rare (e.g., Renault Zoe)
Important
If your EV has a 7 kW onboard charger, it will never charge faster than 7 kW on AC — even if you plug into a 22 kW public charger.
This is one of the most misunderstood parts of EV charging.
AC vs DC Charging
AC Charging (Home & Public AC Chargers)
- Slower
- Uses your EV’s onboard charger
- Typical speeds: 2.4kW–22kW
- Best for overnight charging and daily use
DC Charging (Fast Chargers)
- Much faster
- Bypasses the onboard charger
- Typical speeds: 50kW–350kW
- Best for road trips and quick top‑ups
Why DC is faster
DC chargers send power directly to the battery, skipping the onboard charger’s limitations.
Real‑World Charging Examples
Example 1: 7 kW EV on a 32A Outlet
-
Outlet can supply 7.2 kW
-
EV can accept 7 kW
➡️ Charges at full 7 kW speed
Example 2: 7 kW EV on a 22 kW Public Charger
-
Charger can supply 22 kW
-
EV can accept 7 kW
➡️ Still charges at 7 kW (onboard charger limit)
Example 3: 11 kW EV on Single‑Phase Power
-
Home can supply 7.2 kW
-
EV can accept 11 kW
➡️ Charges at 7 kW (home power limit)
Example 4: DC Fast Charger
-
EV DC limit: 120 kW
-
Charger: 350 kW
➡️ EV charges at up to 120 kW (battery limit)
Frequently Asked Questions
Why does my EV charge slower at home than at public chargers?
Most homes are single‑phase (max ~7.2 kW). Public chargers often supply 11–22 kW AC or 50–350 kW DC.
Can I upgrade my EV’s onboard charger?
No — it is built into the vehicle.
Is 7kW fast enough for daily charging?
Yes — 7kW adds ~30–40 km of range per hour, which easily covers daily driving for most Australians.
Final Thoughts
Once you understand kW, amps, voltage and onboard chargers, EV charging becomes simple and predictable. For most Australian homes, 7.2 kW AC charging offers the perfect balance of speed, convenience and cost. For long trips, DC fast charging gives you rapid top‑ups when you need them.