01 Apr

How fast charging works

How fast charging work

Car battery packs

A car battery consists of many ‘cells’. A single cell is quite similar to a rechargeable battery you use at home only bigger. A Tesla Model S with a 85 kWh battery pack  contains 7,104 individual cells.  A BMW i3 with a 21.6 kWh battery has just 96 cells, but its cells are larger than the cells used by Tesla. Together with all wiring and packaging the cells form the battery pack as depicted below.

BMW i3 Battery

BMW i3 battery pack

Today’s battery packs are designed with fast charging capability. For example the powertrain of the BMW i3 is rated at 125 kW peak power and 75 kW continuous power while fast charging is done at 50 kW.

Battery life

The battery pack of a car is never used 100%. The usable capacity of the 21.6 kWh i3 battery pack is around 19 kWh. The reserve of 2.6 kWh is used to ‘cushion’ the impact of charging and discharging. The battery pack automatically cycles between around 5% and 95% of the battery pack. All of this is handled by the Battery Management System (BMS) and completely hidden from the driver.

There are many factors influencing battery life including heat, battery age, duration of keeping a battery fully charged and number of charge – discharge cycles. Research shows that exclusive use of fast chargers hardly affects battery life when tested with the Nissan Leaf MY2012. And other research indicates that fast charging might actually be better for battery life. As a general rule, a battery will last longer when its size increases because fewer charge – discharge cycles are needed for the same mileage.

Charge speed

During fast charging there is continuous communication between the BMS and the fast charger. The BMS instructs the fast charger to set the charging speed. This speed is usually expressed in kilowatts (kW). Charging a car for 1 hour at 50 kW puts 50 kWh into the battery pack. On average an electric car uses 1 kWh to drive 5 km. Tesla also expresses the charge speed in km/hour. So 50 kW equals about 250 km/hour (‘250 km of range charged in 1 hour’).

P = V * I

Power (expressed in Watts) is the product of voltage (Volts) and current (Amps). When charging at 50 kW this is typically done at 400 V and 125 A (400 * 125 = 50.000 W = 50 kW). Note that this means that the charge speed is influenced by both the voltage and the current.

You can compare charging electricity with running water from a tap. Think of voltage (V) as the water pressure and current (A) as the size of the tap. If you increase the pressure more water will flow, and the same is true when increasing the size of the tap.

The voltage is a characteristic of a battery. Most car battery packs today operate at around 400 V when fully charged. But when a battery pack is not fully charged, the voltage will be lower e.g. 325 V. Voltage will gradually increase while charging, so this has a positive effect on the effective charge speed (see the blue line in the graph below showing a fast charge session of a 30 kWh Nissan Leaf).

The current can be increased or decreased by the fast charger based on data received from the BMS (see yellow line in the graph below). Most fast chargers can provide a maximum current of 125 A, but Tesla superchargers and the upcoming 150 kW CCS chargers can provide more than 300 A.

Nissan Leaf Charge Graph

0-90% charge of a 30 kWh Nissan Leaf

What influences charge speed?

Now let’s take a look at the factors that have an effect on the charge speed other than voltage. There are four main aspects:

Battery pack capacity. In general, a larger battery pack can be charged quicker. So a Tesla Model S with a large 90 kWh battery can be charged quicker than a BMW i3 with a 21 kWh battery. This is also the main reason why most plug-in hybrid electric vehicles (PHEVs) cannot fast charge: their battery packs are simply too small. Most PHEV manufacturers do not include the additional hardware (e.g. extra inlet and wiring) in the car.

State of Charge (SoC). When the battery is almost fully charged the charge speed drops to prevent the battery cells from overheating. Typically at 80-90% SoC the speed drops and charging will slow down further closer to 100% SoC. That is the reason why fast charging is most effective between 0% and 80-90% SoC.

Battery temperature. Battery cells operate most effectively between 20 – 25 degrees Celcius (68 – 77 degrees Fahrenheit). When battery temperature is too low or too high, the BMS reduces the requested current to protect the health of the battery cells. If the battery pack is equipped with a heating or cooling system the BMS will activate this system in order to control the cell temperature. Note that battery temperature is not only influenced by the outside temperature, but also by driving and charging as this will generally increase battery temperature.

Power level of the fast charger. There can be several reasons why a fast charger cannot provide full power. For example the grid connection might not be sufficient for the charger to operate at full power. Or the fast charger needs to share the available grid connection with other chargers on the same location. In that case the chargers will communicate with each other to ensure that the total power used does not exceed the available power of the grid connection. At a Tesla supercharger site two stalls (chargers) typically share their capacity. So if one car charges at full power, there is limited power left for the other car. At Fastned all chargers can work at full power, because we ensure the grid connections are sufficient to deliver peak capacity.

Electric vehicles share a lot of similarities when it comes to the factors that influence charge speed, but the exact impact of each factor differs. For example the 30 kWh Nissan Leaf is able to charge to 90% in the same time as the previous 24 kWh version did. And the BMW i3 can actively heat and cool its battery so temperate will have less impact.

Thank you Roland van der Put for the technical information.

16 Feb

Irish EV Situation

The number of electric cars in Ireland is pathetic. The Department of Transport published the official Vehicle and Driver Statistics Bulletin for 2015 today. It revealed that there are 1,985,130 private cars on our roads at the end of last year but that only 1,028 of them are electric. That is just 0.05 per cent or 5 five hundredths of one per cent. Can you believe it!

Today’s figures also show that in the last year alone a total of 121,110 new private cars were registered but that only 476 of them were electric. That was just 0.39 per cent of new private cars sold last year. Yet ESB was about to introduce charges which would have acted as a significant disincentive for people to switch to electric.

The original Government target was to have 20 per cent of the cars on our roads electric by 2020. Then it was halved to 10 per cent because clearly they did not have a snowball’s chance in hell of achieving that target. But at the rate they are going we will be lucky if they get to two per cent electric by 2020.

Someone needs to take this issue by the scruff of the neck and get the next Government to wake up and take the issue more seriously. The incentives for people to buy electric cars in Ireland are simply not working. The measures need to be improved substantially.

Serious consideration needs to be given to allowing electric cars drive in Bus Lanes and to be able to park for free on our city streets.

Today’s official statistics show there are only 356 electric cars registered in Dublin. That is certainly nowhere near enough to clog up the bus lanes. And overall, the cost of giving give free parking to such a small population of car drivers would be very small indeed.

Yet two little trinkets like those might just grab the public’s attention and cause people take a closer look at switching to electric.

If something radical is not done, and done soon, Ireland will end up with a massive bill for excessive carbon emissions in our transport sector.

Article posted online about the EV Situation in Ireland. fcp-mapwe

19 Nov

A little about Plugs!


The common standard for EV plug type is the IEC 62196.

IEC 62196 is an international standard for set of electrical connectors and charging modes for electric vehicles and is maintained by theInternational Electro technical Commission(IEC).

The standard specifies mechanisms such that, first, power is not supplied unless a vehicle is connected and, second, the vehicle is immobilized while still connected


Charging modes

IEC 62196-1 is applicable to plugs, socket-outlets, connectors, inlets and cable assemblies for electric vehicles, intended for use in conductive charging systems which incorporate control means, with a rated operating voltage not exceeding:

  • 690 V a.c., 50 – 60 Hz, at a rated current not exceeding 250 A;
  • 600 V d.c., at a rated current not exceeding 400 A.

IEC 62196 refers to the charging modes defined in IEC 61851-1 which include:

  • “Mode 1” – slow charging from a household-type socket-outlet
  • “Mode 2” – slow charging from a household-type socket-outlet with an in-cable protection device
  • “Mode 3” – slow or fast charging using a specific EV socket-outlet with control and protection function installed
  • “Mode 4” – fast charging using an external charger


18 Nov

ESB Charging for Chargers


ESB-ecars copy

Beginning later this month, new ESB ecars customers will be asked to sign up to a monthly fee of €16.99 (VAT inclusive). This is a direct quote from ESB.ie. From April 2016, a 30 cent per minute usage fee will apply to fast charging systems.

ESB ecars is working on additional price plans that it will launch in 2016.

The ESB ecars public charging network consists of more than 70 fast chargers located approximately 60 kilometres along inter-urban – capable of recharging a typical EV in 25 minutes, with over 800 Standard chargers in communities throughout Ireland.

A link to the full article can be found here.


16 Feb

Electric Car Range in Ireland

Most of the main car manufacturing brands that sell cars in Ireland have ventured into the EV world, providing a small or family car with a range hovering around the 100km range.

Below are some stats and information on the popularity of EV Models.
Read More

16 Feb

Which EV Charging Plug?

Across the world there are numerous types of EV Charging plugs. These are becoming more standardised according to your location, but the EU have opted to go for the ‘Type 2’ plug.