ELECTRIC cars are a new technology with different standards that require familiarisation.

To help, I’m getting my head around it all – and plan to blog my findings as I do so.

Creating a sort of motoring journo-level EV 101: all you (and we) need to know about electric cars.

Where do we begin? With the basics. An EV spec sheet contains lots of jargon that makes no sense at first. Here’s my take on demystifying the standard stuff.

•    What is an electric car?
A combustion engine is replaced by an electric motor. Instead of a fuel tank, modern electric cars use lithium ion batteries.

An invertor is needed to convert battery DC power into EV’s favoured AC power. A power control module is required to control the power. Most electric cars also feature an onboard battery charger module (no hunting for the charger, mobile phone style!).

•    What makes an electric car move?
Power from the battery is transmitted to the electric motor via the transformer, under the watch of the power control module. In the motor, it is turned from electromagnetic force into a torque.

This turning effect drives a shaft that turns the wheels.

Motor type
2 main types: DC brushless and AC.

DC

Brushless DC motors dominate for hybrids and plug-in hybrids. Peak point power efficiency is higher: for their size, they pack a punch. However, the magnets for them are costly – and, as they get bigger, magnetic losses grow. They are thus not ideal for higher-output EVs.

The little smart ev uses a 55kW brushless DC motor, though (it’s light and will only ever seat 2, so can get away with it).

AC

These motors rule for EVs (hence the power invertor they all have). Just as there are various engine layouts (inline 4, V6, etc), there are also different motor types.

EV AC motors use the principal of a rotating magnetic field, as discovered by Nikola Tesla (for it is he). Basically comprise an outside stationary stator. The coils within it are fed with AC current, creating a rotating magnetic field.

Inside, there is a rotor, attached to the output drive shaft. This is turned by a form of interaction with the rotating magnetic field. Currently, two key types are on the market.

•    AC Synchronous
Current is supplied direct into the rotor, creating a magnetic field around it. The rotating magnetic field in the stator induces a torque on this stationary rotor field, causing it to rotate in time with it. Hence, the synchronous classification.
Used in: Nissan LEAF (80kW), Renault Fluence (70kW), Mitsubishi i-MiEV (47kW)

•    AC Induction
NO direct current supply to rotor. Instead, it’s induced by the rotating magnetic field – the conductors on the rotor are ‘excited’ and try to follow this round: rotating as they do so! They don’t catch it up though: there’s always a difference in rotation speeds. This is the slip ratio.
Used in: Tesla Roadster (185kW), MINI E (150kW).

Electric car units
•    kW
Power output of an electric motor. Directly proportional to bhp: 1kW = 1.341hp  (150kW = 201bhp).

•    kWh
Energy capacity of a battery: the maximum kW that can continuously be produced for an hour. Familiar to home owners: it’s how electricity companies calculate domestic usage.

•    Energy density, Wh/kg
How much a battery can hold. Higher is better – means a longer running time!

•    Power density, kW/kg
How much it can deliver on demand. Focus here is on power bursts rather than a long running time.

Battery type
Lithium ion batteries dominate for electric cars. They store more energy, are lighter and have a longer lifespan than older batteries such as NiMh.

There are various different chemistries. The chemistry of the battery determines its electrochemical performance. The characteristics of each will be covered in due course!

So…

What next? Well, for me to become an EV rockstar, that’s what. The (even) harder work thus begins, for a journo who, for 3 decades, has been firmly combustion-based…

Do come back to find out how I get on.

+ How well do you understand electric cars?
+ Do you find the different measurements easy to understand?
+ How daunting do you reckon explaining EVs to readers will be?

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