Sold on the idea of an electric vehicle, but afraid to take the plunge? You’re not alone. For most of us, EV plug-in technology still remains a mystery in a world driven by internal combustion engines (ICEs). But EVs aren’t all that complicated. Here’s a look under the hood to show you an EV’s components and how they work together to get you from here to there. We’ll follow the path of the energy, from its source as electrical energy to its final application as mechanical energy at the drive wheels.
Once programmed with a charging profile that matches your electric vehicle’s battery pack (which provides the “fuel”), a charger brings the alternating current (AC) from the grid or an RE system into the vehicle, and converts (or “rectifies”) it into direct current (DC) to charge the batteries. Depending on the model, a charger may either automatically shut off when the batteries are fully charged, or drop to a low-current finish charge and hold there. The type of charger you use is a matter of preference, but if the car will sit idle for a day or more, you might want the auto shutoff feature. This way, you don’t have to worry about overcharging the EV’s batteries or wasting energy.
The majority of chargers accept 120 VAC input from a standard household outlet. Other chargers require input from a 240 VAC receptacle (such as a clothes dryer outlet) to more closely match the higher voltage of the vehicle’s battery packs. Though 240 VAC outlets are harder to find when you’re away from home, they provide a faster charge than 120 VAC outlets. A typical EV battery pack, if completely drained down to 20% of full, takes about 8 to 12 hours from 120 VAC to be fully recharged—versus 4 to 6 hours from 240 VAC. The higher voltage input to the charger makes the higher charging current possible.
Be sure to match the charger to the battery pack. Charging too quickly can damage some battery types, and charging too slowly can damage others. A few chargers accept both 120 and 240 VAC input, but these dual-duty chargers are larger and more expensive than single-input models. For charging flexibility, a 120 VAC charger can be kept onboard for opportunity charging and a 240 VAC charger can be used at home for faster charging.
From the charger, electricity flows to the battery pack through its positive and negative terminals. In the battery, DC energy is stored by a chemical reaction. An electric load (in this case, the EV’s motor) connected to the battery posts causes the chemical reaction to reverse, releasing energy to the load.
A battery’s suitability largely depends on several factors in its design—including the number of plates and their thickness, the ratio of plate material to electrolyte, and the shape of the plate. The most common batteries in EVs are lead acid, nickel metal hydride, or lithium ion. Batteries in EV conversions can be sealed or flooded, and are typically lead acid. Flooded batteries need to have water added periodically. The sealed batteries generally found in factory-built EVs do not require maintenance.
An EV’s batteries are wired in series, which means a daisy chain of connections from the positive post on one battery to the negative post of the next. This type of wiring adds the voltage of the individual batteries to build up a higher voltage pack. Battery-pack voltage can be as low as 36 V to 72 V for neighborhood electric vehicles (NEVs), or from 96 V to more than 300 V for a full-function, highway-capable EV.