The usable capacity of the 21.6 kWh i3 battery pack is around 19 kWh or about 90% of the total capacity. The battery pack of a car is never used 100%. 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. Today’s battery packs are designed with fast charging capability. Together with all wiring and packaging the cells form the battery pack as depicted below. A BMW i3 with a 21.6 kWh battery has just 96 cells, but its cells are larger than the cells used by Tesla. A Tesla Model S with a 85 kWh battery pack contains 7,104 individual cells. A single cell is quite similar to a rechargeable battery you use at home, only bigger. More on the impact of this later.Ī vehicle battery consists of many ‘cells’. The next generation of fast chargers was introduced in early 2018 and delivers 175 kW and can even be upgraded later to 350 kW. A very common fast charger delivers 50 kW which charges a vehicle about 5 to 15 times faster than an onboard charger. That is why they are usually referred to as ‘DC fast chargers’ or just ‘fast chargers’. So vehicle manufacturers usually choose a relatively small - and therefore slow - onboard charger to optimise between these factors.Īn external charger that does the AC/DC conversion can be a lot bigger, heavier, more complex and more expensive than an onboard charger. On top of that any component in a vehicle needs to be automotive grade to ensure its reliable operation for the lifetime of the vehicle. But a bigger charger is heavier, takes up more space in the car and adds complexity and cost to the vehicle. If you want to charge faster, the AC/DC converter and hence the charger need to be bigger. So a charge point is not actually a charger but an intelligent socket to plug in your charge cable. The charge point delivers the AC required for the onboard charger to charge your battery. You can use a cable to connect the onboard charger to a regular AC socket in your garage or plug it into a charge point. Today, virtually all electric vehicles have a small onboard charger. Chargers can either be integrated into the vehicle as an onboard charger, or chargers can be external to the vehicle (for example a fast charger). This AC/DC converter is part of what we call a charger. Therefore AC from the grid needs to be converted to DC so it can be used to charge the battery. But the electric grid delivers Alternating Current (AC). What is fast charging? And how is it different from ‘regular’ charging? All batteries - including those in electric vehicles - use Direct Current (DC) for charging and discharging.
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