How Plug-In Hybrids Work

Dave Nichols
Sep 2023
It will drive you around town on electricity alone but also has a fuel-efficient gasoline engine married to an electric motor. So, how does a plug-in hybrid actually work? Read on to find out.
Man Driving car with control panel visible

How Do Plug-In Hybrids Work?

A plug-in hybrid car is a gasoline- and electric-powered vehicle (PHEV) that uses a rechargeable battery to power an electric motor. The car will generally run on all-electric power for 25 miles or so before the battery is depleted. Once that happens, the vehicle will automatically switch over to the gasoline-powered internal combustion engine.

From playing music on the stereo to spinning the wheels, plug-in hybrids harness the needed energy from both electric and gasoline components. Although many of the electrical components function similarly to those found in all-electric cars, there are some important distinctions to be aware of. Let’s look at the two different types of vehicle components: electric and gasoline.

Plug-In Hybrid: Battery

We begin with the traction battery pack, which stores all the electrical energy in the car and powers all the electrical components in the vehicle. Most modern EV batteries are made from lithium because they can store a lot of energy while also remaining relatively lightweight. Assuming every EV has the same electrical efficiency, it would be fair to say that a bigger battery stores more electrical energy in the vehicle, thus translating into more electric range. BEVs tend to have the largest batteries, followed by PHEVs then HEVs.

electric car components and motor

PHEVs Electric Motor

Using the electrical energy stored inside the traction battery pack, the electric traction motor converts electrical energy into mechanical energy. The vehicle’s transmission then transfers that mechanical energy from the motor to drive the wheels. Depending on the number and placement of these motors, a PHEV’s drivetrain can either be front-wheel drive (FWD), rear-wheel drive (RWD), or all-wheel drive (AWD). 

PHEVs also come standard with a useful energy recovery mechanism called regenerative braking, which is controlled either by the motor or another component known as a generator. Regenerative braking occurs when the driver takes their foot off the acceleration pedal, prompting the generator to spin (or the motor to act in reverse) and convert unused kinetic energy into electrical energy. The energy is then stored in the battery, ready to power the motor again. In other words, this mechanism recovers energy using the vehicle’s momentum to use less electrical energy and extend the battery’s state of charge.

person plugging in car charger

Charge Port & Onboard Charger

 In PHEVs, the battery pack is charged through an external power source using the appropriate charging plug (found on the cord) via the charge port (found on the car). This plug is the EV equivalent of a fuel nozzle at a gas station and the charge port is like the opening where you insert the nozzle.

Working in tandem with the charge port is the onboard charger. Think of this as the computer that is responsible for converting the plug’s native electrical current into an acceptable DC power level to charge the battery. The onboard charger does the thinking and converting so the driver doesn’t have to, ensuring the battery is not harmed by the wrong type of charger. 

close up of electric car components

Gasoline Components

As mentioned above, PHEVs also come equipped with an internal combustion engine to power the car using another fuel source (typically gasoline or diesel) once the traction battery has been depleted. This is possible through the design of the vehicle’s transmission, which can select either the combustion engine or electric motor as a power source. Since PHEVs can run on two different energy sources, there is a second fuel lid in a separate location to refuel the vehicle with gasoline. This fuel filler is the same as found on all gasoline-powered vehicles.

PHEVs also come equipped with an advanced exhaust system to channel away emission byproducts generated by the chemical reactions in the engine. Depending on the PHEV model, the exhaust system is fine-tuned to release lower emissions than traditional gas vehicles and is certified to a certain tailpipe emission standard.

car charger in station

Recharging Plug-In Hybrid Cars

The onboard chargers of most PHEVs are only equipped to handle AC power, which can be extracted from standard home wall outlets and public Level 2 charging stations. DC fast chargers are considered too powerful for most PHEVs due to their lower battery capacities and onboard charger restrictions.

Due to their heavier reliance on internal combustion engines, there has been little innovation to make this change in PHEVs. Automakers don’t expect this feature to come anytime soon. However, this does allow PHEVs to forgo the option of charging altogether and travel solely on gasoline.

Once solid-state batteries become the norm, EVs will have a range of up to 500 miles, eliminating the need for Plug-in Hybrids altogether.

Front view of a Tesla Model 3 driving through canyon roads

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