MPGe, kWh, 4xe? Everything You Need to Know About Electric Car Lingo
Now that you know the difference between BEVs and PHEVs, it’s time to dig deeper.
There are tons of unfamiliar terms, acronyms, and measurements thrown around in the EV world, and they can get overwhelming pretty quickly if you haven’t had the luxury of following EV development for the past few years. But you don’t have to worry—this guide will teach you everything you need to know about all those strange little words so you can become a formidable expert on electric technology before you know it.
Welcome to Alternative Power Week! In honor of Earth Day, we’re going to spend the next several days diving into the nitty-gritty of the new, eco-friendly technology powering the vehicles of the future to keep you informed on all the latest changes in the automotive industry. If you have any questions or ideas for a future article, leave your ideas in the comments!
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kWh: Kilowatt Hour
The kilowatt hour, or kWh, is a way to express a battery’s capacity, and it stands for the amount of energy expended in one hour by one kilowatt of power. Here’s a simple way of looking at it:
- A kilowatt is the rate of energy flow. So, it would be similar to the number of gallons per minute that a gas pump could deliver.
- A kilowatt-hour is a quantity of electricity, like a gallon. The more kilowatt hours, the more electricity.
- If you run a one-kilowatt EV charging station for one hour, it will deliver one kilowatt-hour of electricity. If you run a 50-kilowatt charging station for one hour, it would provide 50 kilowatt-hours of electricity.
This can get a little confusing for folks that are new to the BEV world, but you can generally expect a battery with a higher kWh capacity to be capable of a longer range. It’s the opposite of a gasoline-powered car’s miles per gallon rating; you want your mpg to be lower but your kWh to be higher.
That being said, it’s not as accurate a measure as, say, miles per gallon, because kilowatt-hours refers only to the battery capacity, not how far that battery can go. Miles per gallon, on the other hand, refers to the distance traveled based on one gallon of fuel and does not rate the capacity of the fuel tank.
Think of it this way: imagine two internal combustion engine cars. One is a large SUV and one is a tiny city car, and both are rated to travel 25 mpg. That means that, no matter how large or small the vehicle, both will travel the same distance on one gallon of fuel.
But because batteries measure capacity and not distance, a large SUV and a small city car can both use the same 60 kWh battery and travel completely different distances. The heavier, less aerodynamic SUV will use more energy, or kilowatts, to travel, while the lighter, more aerodynamic city car can drive farther with the same capacity.
This is why, in many cases, electric vehicle product descriptions will include several different power-related measurements, like kWh, MPGe, and RPH.
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MPGe: Miles per Gallon Equivalent
The Environmental Protection Agency realized that it can be tough to visualize kWh and so introduced MPGe, or a miles per gallon equivalent. This measurement is designed to help compare BEVs and ICEs on a one-to-one ratio.
The conversion is fairly simple: one gallon of gasoline equals 33.705 kWh of electricity. So, the number of miles a BEV can travel in 33.705 kWh will serve as its MPGe.
It’s important to note that this metric isn’t of much use when it comes to determining how much it costs to charge your battery; it’s strictly a matter of distance traveled in comparison to an ICE car. And it also doesn’t tell you the range, or how far your BEV can travel with its battery.
RPH: Range Per Hour
RPH, or range per hour, doesn’t necessarily refer to how far your EV can travel in one hour; instead, it’s a unit of measurement designed to measure how many miles a charger can provide in one hour.
So, if a charger says it has 100 RPH, that means that, after one hour of charging your BEV, you’ll be able to travel 100 more miles.
We’ll talk about the different levels of chargers in just a moment, but generally, the higher the level, the more RPH you’ll get. When you’re on a road trip, you’ll want to hit those ‘fast’ chargers that advertise a higher RPH.
4xe
4xe is a new term specifically used by Jeep for its Jeep Wrangler 4xe. Basically, it uses a pair of electric motors to help power the traditional 4×4 off-road driving system. Now, let’s get into the specifics.
The Jeep Wrangler 4xe features a 2.0-liter turbo four engine in the front, which sends power to the transmission and to the transfer case. The transfer case splits that power between the axles in the front and back. One electric motor is built into the transmission, and one is directly attached to the engine.
The motor in the engine doesn’t generate electricity, but it uses electricity generated by the internal combustion engine to essentially give you a little boost by applying massive torque to the engine, which will help you conquer obstacles while off-roading.
The motor in the transmission does something similar in the way it applies extra power to the driveline which also helps to increase power.
This is a plug-in hybrid, so these batteries do need to be charged, but the electric motors are designed to provide a little extra oomph to those who need it.
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Charging Levels
Right now, there are three different levels of charging that you can count on when it comes to powering up your battery:
- Level 1 (5-10 RPH). A Level 1 charger can be plugged into a normal 120-volt household outlet, so if you’re new to the EV life, this will be the most likely option you’ll have for home charging without needing to install a larger system. As you can tell, though, you’ll have to leave your car charging all night to regain even a smidge of range.
- Level 2 (20-25 RPH). Level 2 chargers are the kind you’ll see in public, like at work or in apartment buildings—but you can also have one installed in your home. These will provide more range if you have it plugged in overnight or during the work day, but it’s also not ideal for efficiently recharging on a longer road trip.
- Level 3 (100-2000 RPH). Level 3 chargers are also called DC Fast Chargers, or DCFC. They’re designed to charge your battery as quickly and efficiently as possible. You’ll find these in commercial charging centers or at highway rest stops, since they’re designed to get you back on the road quickly. Right now, you’re most likely to find 200 RPH DCFC chargers, but more 600 DCFC chargers are being installed. The technology exists to provide 2000 RPH, but it costs a lot of money, and most vehicles on the market don’t accept that much power; you’ll likely see more of these in the future.
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Regenerative Braking
If you’ve been looking into BEVs, you’ve probably heard of both regenerative braking and one-pedal driving. We’ll start with the former first.
To put it simply, braking generates energy. In regenerative braking, a battery captures and stores that brake-induced kinetic energy, which prevents the battery from running out of energy as quickly.
Regenerative braking is the reason why conventional hybrids, or HEVs, don’t need to be recharged; the small hybrid motor’s battery is topped up every time you hit the brakes.
BEVs and PHEVs also utilize regenerative braking, but they do need to be charged up because they use the battery power generated during charging as a first line of defense. In these instances, regenerative braking serves as a way to preserve battery life.
One-Pedal Driving
One-pedal driving is exactly what it sounds like; you can accelerate and decelerate without ever using the brake pedal. This feature is common on many new EVs and PHEVs because it depends upon the concept of regenerative braking.
In one-pedal driving, you just have to ease off the accelerator pedal to begin coming to a stop. It can take a little longer to come to a full stop than in a vehicle that uses a conventional braking system, but once a driver fully stops, the traditional hydraulic braking system kicks in to keep the driver in a stopped position until she presses the accelerator again. And yes, any time your car is slowing, the brake lights kick on.
To be more specific, when letting off the accelerator, you will start to decelerate at a force of 0.2 Gs, which is about 20 percent of the full hydraulic braking force. So it’s going to take a longer time to stop.
But during the time your car is slowing down, your battery is saving up more kinetic energy than it would while using a traditional hydraulic brake stop.
It can take some time to get used to one-pedal driving, since it requires an entire recalibration of your spatial perception and brake distance judgement. But once you get the hang of it, you’ll notice a tangible difference in your battery life.
It’s also important to note that the hydraulic brake pedal is still available on these cars, which will come in handy as you get used to the longer stopping distances of one-pedal driving. It’s also the pedal you should use in emergency stopping situations.
EPA vs. NEDC vs. WLTP
If you’ve been looking at BEVs, you might notice that, depending on where you look, the estimated range is dramatically different. That’s because there are three different testing standards that are currently used to determine EV range: EPA, NEDC, and WLTP.
Because A Girls Guide to Cars is a North American-based publication, we’ll be using ranges determined by the Environmental Protection Agency, or EPA. It’s the standard we use in the U.S. The other two testing standards, the New European Driving Cycle (NEDC), and the Worldwide Harmonized Light Vehicle Test Procedure (WLTP), are European-based.
Each of these testing standards will produce wildly different range estimates due to the varying emphasis on highway versus city driving.
For example, in the U.S., we do a lot of highway driving, so the EPA range figures take that into consideration. In Europe, where massive highways are rare, testing standards are based more on urban and suburban travel.
Every testing system is different. Here are how the three ranges are determined, ranked from most to least accurate:
- EPA: EPA testing procedures are the most rigorous and thus create range estimates that are most reflective of driving on American roads. The EPA does a multi-cycle test, which involves fully charging the battery, letting the battery sit overnight, and then testing the car the next day on different simulated highway, city, and steady-state driving conditions until it is completely out of charge. The EPA will then recharge the battery and do the test all over again, after which point it determines an estimated driving range.
- WLTP: WLTP standards were introduced in Europe in 2017 as a way to develop more accurate results than the NEDC. It uses a dynamic test cycle that includes a wider variety of urban and non-urban driving conditions and also uses a variety of speeds, shift points, and temperatures to create a more accurate reflection of the real-life range. It’s less accurate than EPA standards but is more accurate than NEDC.
- NEDC: What makes NEDC standards so ineffective? It takes a lab-based approach to collecting range data under ideal conditions rather than attempting to mimic actual real-world driving conditions. As a result, the NEDC overestimates range capacity by 25 to 30 percent compared to what you’d experience in the real world.
So, if you live in America, you’ll depend on EPA standards. In Europe, you’ll want to look for WLTP numbers.
Categorized:Electric Cars Car Technology