How Fast is Fast when Charging?
So how fast can you charge your electric vehicle? It depends on a number of factors, and there is no defined meaning of the words fast or rapid. So you have to dig further to understand how long it will take to charge the vehicle.
SoC – State of Charge
SoC stands for “State of Charge” and is in percent (%). 100% is fully charged (12 bars on a LEAF).
The vehicle can limit the speed of charging. For instance a Gen 1 or 2 Nissan LEAF only charges at a maximum of 3.6kW.
The battery size also plays a part.
The type of charger (its mode) and the amount of capacity available can limit the amount of charge.
With a single phase installation, the EVSE is limited to 7.2kW. With 3 phase power the maximum the EVSE can provide is 22kW.
Calculating Time to Charge
Step 1: Determine the maximum rate of charge that can be accepted by the vehicle.
Step 2: Determine the maximum rate that can delivered by the charger. A JuiceBox 32 (32 Amps) in single phase is 7.2kW and in 3 phase is 22kW. A JuiceBox 40 is limited to single phase 32A which is 7.2kW.
Step 3: Take the smallest number from Step 1 or Step 2.
Step 4: Determine the vehicle’s battery size in kW.
Step 5: Divide step 4 by Step 3 to get the approximate charge time in hours for a full charge from empty 0% to 100%.
Note – while the JuiceBox is very efficient (it just needs a little power for the smarts and control) the AC to DC conversion in the car is only about 92% efficient.
Example using Nissan LEAF
Gen 1 or Gen 2
Step 1: 3.6kW
Step 2: 7.2kW – Assuming single phase JuiceBox 32 or 40
Step 3: 3.6kW
Step 4: 24kWh
Step 5: 24kWh/3.6kW = 6.666 which is less than 7 hours for a full charge.
Some other Examples:
A Nissan LEAF, Mitsubishi Outlander, Renault Kangoo and the previous BMW i3 charges at 3 kW (single phase AC). This is considered to be slow charging in NZ. The new BMW i3S charges at 11kW using AC 3-phase (the JuiceBox) and 50kW DC (3-phase) using a DC rapid charger like the Tritium VeeFil.
The JuiceBox 32 with 3 phase input can charge up to 22kW (Renault Zoe), and can be set at any power from 4 to 22 kW maximum. The JuiceBox 32 will also charge from single phase up to 7.2kW. It also does load sharing if you have more than one EV to be charged at a time in the same premise.
How long to charge 18kW?
Examples to add 18kW of charge which is a normal charge when you get down to the “charge now” warning in a LEAF or Hyundai Ioniq.
|Vehicle||Maximum Vehicle Rate||Time|
|Nissan LEAF J1772 (Type 1)||3.6kW/hr||6 hours|
|UK import Tekna LEAF J1772 (Type 1)||6.6kW||3 hours|
|Hyundai Ioniq||6.6kW||3 hours|
|BMW i3||11kW||Less than 2 hours|
|Renault Zoe||22kW||Less than 1 hour.|
|Tesla||22kW||Less than 1 hour.|
|Using a Domestic 10A Socket||1.8kW||10 hours|
How Slow then is a Domestic 10A Outlet?
Worksafe requirements limit the amount of power that be drawn to 8A or 1.8kW. This is referred to as trickle charging.
Currently the worst case example would be a Tesla Model X with 100kWh battery. Therefore 100kWh divided by 1.8kW is 56 hours or over 2 days!
It is feasible to charge a 24kWh Nissan LEAF at 1.8kW as its only 12 hours to fully charge from empty to full. However it is discouraged in the manual.
With EV battery sizes increasing as the price is reducing, and higher power chargers in vehicles (for example Renault Zoe) becoming more common, installing a hardwired JuiceBox that can charge at 7.2kW to 22kW is a better, future proofed approach.