Go "Behind the Charge" with Electrify America's Director of Charging Infrastructure Planning and Business Development - on "Charging Electric Vehicles in Cold Weather"
‘Behind the Charge’ takes viewers behind the scenes at Electrify America, interviewing employees across fields and exploring different features at the fast charging network to answer commonly asked questions.
For many, this winter has been more of a challenge than normal across many states. Electrify America recognizes that electric vehicle (EV) charging is a new experience for drivers who may have purchased their first EV, and they may not know that frigid winter temperatures can have an impact when charging their EV.
Go ‘Behind the Charge’ with Wayne, Electrify America’s director of charging infrastructure planning and business development for answers questions about cold weather charging, the impact of temperature on charging range and the charging rate.
Why do electric vehicle (EV) drivers see their vehicle charge at a speed below its advertised peak charging power?
Wayne: The charging rate is actually controlled by the battery of an electric vehicle, not the charger, and it depends on a number of factors – including battery condition and initial state of charge, vehicle condition and ambient temperature. With all EVs, charging power is typically reduced in colder weather, sometimes dramatically. This is because the chemical processes in the batteries prefer a temperature of 60 to 80 degrees Fahrenheit to best transfer electrons within the battery and thus process the highest optimal charge power of the vehicle. It’s also important to note that the vehicle’s charging rate will always decrease during a charging session as the battery reaches full capacity to optimize battery durability and service life.
Can you tell us more about charging power rates and what EV drivers should expect?
Wayne: After the charging session starts, the EV battery continually advises the charger of what amperage and voltage it needs at regular intervals, so the charger can refill the battery at the optimal power rate appropriate to the conditions. Again, temperature, battery age and state of charge are all key factors in a battery’s charging power rate - and the EV’s battery and software determine the charge rate, not the charger.
I was trying to the charge my EV in cold weather – does temperature impact the charging rate of an EV?
Wayne: EV batteries are designed to operate optimally and deliver maximum charging power capacity between 60 to 80 degrees Fahrenheit. Temperatures below 40 degrees Fahrenheit can dramatically reduce charging power -- oftentimes to less than half of the vehicle’s peak charging power. At these lower temperatures, the chemical processes involved in electron transfer within the battery slow down and are not able to take in as much power as a result. In these instances, the EV’s software reduces charging power to avoid stressing the battery to maximize durability and longevity.
Can an EV also lose mileage range due to cold weather?
Wayne: Definitely. Even if an EV driver charges up to 80 percent State of Charge, or what we call a ‘bulk charge,’ cold temperatures overnight can drop an EV’s range by as much as 30 miles or more. Some EVs automatically compensate for the available range by predicting this reduction during cold weather conditions and informing the driver via the console display or charging app. In addition, some automakers have a warning light alerting the driver to park indoors if possible, to preserve the mileage range of the battery in cold weather. Finally, driving a fully charged EV in colder weather does naturally reduce its driving range, partly because the battery chemical processes are not operating as efficiently in the lower temperatures.
Why do we see charging rates below the EV’s advertised peak charging rate - even in warmer weather, or when the EV is at 0 to 80 percent State of Charge – the ideal window for faster charging?
Wayne: Much like a cell phone battery, an EV battery experiences its fastest charging rates up to about an 80% percent State of Charge. However, the charging power rate is different for each EV model and automaker, but in all cases – the EV’s battery and controlling software ultimately control the charging speed. After the charging session starts, the EV continually advises the charger of what amperage and voltage it needs at regular intervals, which can lead to varying charging rates. Above approximately 80% State of Charge, all EVs slow down their charging rate to more evenly fill up the individual battery cells as the maximum State of Charge is reached.
I’ve heard that some EVs have a feature that prepares the vehicle to warm up the battery before charging. Is that true?
Wayne: Some EVs do have a pre-conditioning feature which allows the driver to program or manually warm up the battery to more optimal temperatures, which can help restore the battery charging power to more normal levels. It’s important to note, however, that the preconditioning process does use some battery power to provide the warming effect and this can reduce driving range. However, many EVs have a more than adequate range for an average driver’s daily needs, so the reduced mileage may be an appropriate trade-off for faster charging.
Do you see future battery technology making EV travel more seamless in the future?
Wayne: We are very encouraged with the rapid development of electric vehicle technology coming in the near term. Automakers and battery developers are accelerating their research and development with significant investment to meet the ever increasing demand for electric vehicle transportation. Our whole industry has seen tremendous progress in just the last two years. We are excited to see what automakers offer next, and believe our charging infrastructure can play an important role in the future of eMobility.
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