Simple Guide to Understanding Plug-in Hybrid Cars


Feb 17th, 2020

Simple Guide to Understanding Plug-in Hybrid Cars

It might come as a surprise, but not most people know what hybrid means when used in reference to cars. On paper, most of us will quickly tell a hybrid vehicle from the others. However, the same can’t be said when you ask what exactly makes a car hybrid.

What is a Hybrid Car

Hybrids, unlike conventional diesel or petrol cars, make use of two powertrains – an electric motor and a petrol engine.

The Bridge between Petrol and Electric Powertrains

Hybrids are perceived to be the nexus between electric and petrol powertrains. As such, they inherit many advantages from both ends. For one, electric motors have efficient acceleration. They also deliver more power from a dead stop state compared to internal combustion engines. 

Nonetheless, they are still limited. Batteries with enough capacity to last long drives are expensive and bulky. In Hybrids, the electric motors augment the power developed by the smaller but efficient internal combustion engines. 

Since hybrids have a petrol engine, the size of their battery packs is smaller compared to that of pure EVs. 

Plug-In Hybrid EVs (PHEVs)

PHEVs extend the hybridisation concept by using larger capacity batteries that can be recharged using an external electrical outlet or at a charging station. The on-board engine can also charge the battery. PHEVs have a system that allows emissions from the tailpipe to be displaced to the generators powering the grid. 

Depending on the car model, the generators can either be renewable or have a lower emission. Recharging the battery using the grid is cheaper than using the gas engine. 

They can store more electric juice such that their petrol usage is significantly reduced. 

Plug-in hybrids typically run on electricity for short commutes. 

Automakers dub their plug-in hybrids differently. For instance, Chevrolet’s “extended-range EV” – Volt is a plug-in hybrid. The Volt offers a full EV experience for commutes within the driving range that can be supported by the battery. For distances that are out of this range, the car will switch to the gas engine.

Mode of Operation

Although all plug-in hybrids have an electric motor and a gas engine, they vary in operation, which is either of three different modes. They can be charge-sustaining, charge-depleting, or mixed-mode, which is a combination of both. 

Charge-Depleting Mode

For the charge-depleting mode, the vehicle runs on electricity from the battery until it is depleted to a predetermined level. At this point, the car will then revert to and engage the gas engine for the rest of the drive. 

The period where the vehicle runs (almost) exclusively on electricity is its all-electric range.

Charge-Sustaining Mode

For the charge-sustaining mode, the vehicle uses both petrol and electricity as the battery is recharging.

Blended Mode

Some hybrids make use of both modes - they can switch between the two modes depending on the driving conditions. Such hybrids are referred to as blended mode plug-ins. 

Key Components of a Plug-In Hybrid EV

Here are the key components of PHEVs.

The Battery

It provides electric power to start and keep the vehicle running. The battery also powers almost all the car accessories and systems.

The Charging Port

This port is used to connect the car to an external electric outlet for recharging.

DC to DC Converter

Car accessories need a low voltage to operate. However, the DC voltage obtained from the battery is sometimes too high. The car uses a DC to DC converter to step down the high voltage to a lower voltage.

Electric Generator

It generates electricity from the braking action of the vehicle. The power is transferred back to the battery. The electric traction motor drives the wheels. Some car models use a motor-generator as it can handle both drive and regeneration functions.

Fuel Tank

It stores fuel that is used to power the vehicles when it reverts to the petrol engine.

On-Board Charging System

The on-board charging system is used to charge the battery pack. It converts the AC electricity from the charge port to DC. It also monitors the battery conditions as well as performance parameters such as voltage, temperature, and current.


The powertrains of PHEVs are similar to those of conventional hybrids. They include series, parallel, and series-parallel.

Series Hybrids

These are propelled exclusively by the electric motor in that only the electric motor turns the wheels of the vehicle. The petrol engine provides electricity to power the motor.

An example of a series hybrid PHEV is the Chevrolet Volt, not to be confused with the Chevy Bolt, which is its purely-electric sibling. 

Parallel Hybrids

Unlike series hybrids, these are propelled by the engine and the electric motor concurrently. The engines and electric motors of parallel PHEVs are connected to and can both turn the wheel. 

Some parallel hybrids, under specific conditions, can occasionally switch to series when it is efficient. The electric-only propulsion mostly occurs at low driving speeds for parallel hybrids. The Honda Insight is a parallel hybrid car.

Series-Parallel Hybrids

Series-parallel hybrids, as the name suggests, combine both characteristics and operate in either configuration. 

The Toyota Prius is a perfect example of a series-parallel hybrid PHEV.

Pros and Cons of PHEVs

PHEVs are characterised by economical petrol consumption (roughly 30% to 60% less) compared to conventional internal combustion engine vehicles. 

They also emit less gas, the volume of which depends on how electricity is generated.

Plug-in hybrid vehicle units cost more than conventional hybrids and regular cars. However, the fuel cost for hybrids is much lower since electricity is cheaper than petrol.

Another downside of PHEVs is the long time it takes to recharge. Recharging from a 120-volt household outlet takes time. Recharging using a 240-volt house or public outlet takes roughly 2 to 4 hours. However, a 30-minutes fast charge can give the car enough battery juice.  

You may refer to our other article to compare PHEVs with fully-electric vehicles, or bookmark our site for updates. If you wish to search for online auto parts stores, there’s no need to go far. You can do it here through our buy and sell platform at!


Sam O.