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Engineers have a trick to help electric vehicle batteries get more range in winter

A simple tip from the engineers who develop and test electric vehicles can reduce or eliminate one of owners’ biggest concerns: the effect cold weather has on electric vehicles’ driving range.

Everything about EVs is new. We’re all on a learning curve, but one of the most important habits owners can develop is heating the interior while the car is plugged in, before leaving home, said Bryan Roos, who led the writing of a new standard to help owners, manufacturers and regulators keep the vehicles useful year-round.

“The effect temperature has on pure battery range is decreasing as the technology improves,” Roos said. “On a cold day, most of your range deterioration is based on the greater draw from (climate control). Not your battery.

“The best way to reduce that impact is to precondition your vehicle’s temperature.”

It’s not uncommon for the gauge that predicts driving range to show a fully charged battery that will carry you 30% fewer miles when the temperature falls to 20 degrees Fahrenheit. Some owners report much larger decreases.

The best new EVs’ batteries, for most owners, will get them through a day’s drive even at that level. Do you panic if your gasoline car only has three-eighths of a tank when you leave for work in the morning? Still, seeing “projected range 110 miles” is unnerving, and makes some people wonder if they can rely on the new technology.

Recharging a battery takes longer than pumping gas, and tow trucks aren’t equipped for quick electricity top-ups yet. Range anxiety remains a concern, though most EV owners report quickly discovering it barely affects their daily routine.

“The majority of the population does a lot of short trips,” said Roos, who is energy architecture lead for battery-electric vehicles at General Motors as well as drafting lead for the just-updated standard by SAE International, the U.S.-based engineering society. Manufacturers and governments rely on SAE standards to test for fuel efficiency, range, power and more.

The standard, called J1634, estimates the impact of warming the passenger compartment up while a vehicle’s plugged in, before it starts drawing on the charge in its battery.

Nearly all EV owners will charge their vehicles at home every night, so they start every day with a full charge and can take advantage of lower off-peak electric rates.

'A huge advantage'

“Cabin heating and cooling is a big deal,” Roos said. “Using the grid to precondition cabin temperature is a huge advantage on short trips.” The impact is reduced on long trips, but doing the initial big change in temperature while plugged in rather than using the battery still has an effect.

There’s some loss of range associated with cold ambient temperatures’ effect on vehicle systems other than climate, but it’s actually less than gasoline vehicles, because EVs don’t use a lot of lubricants that are sluggish and inefficient when a cold vehicle starts, Roos said.

For maximum driving range, owners should use a remote or program the vehicle to precondition interior temperature while it’s plugged in. That also makes the vehicle’s battery more efficient, by warming it to optimal temperature.

The process doesn’t require much more planning than millions of people already do with remote starters on cold mornings and hot afternoons.

“You greatly reduce the climate control system’s impact by powering while you’re plugged into the grid,” Roos said. “The new standard compares the effect of wall-conditioning on the cabin and battery. We’re also quantifying the amount of wall energy used by plugged preconditioning,” so owners can check their electric bill to see just how much they save by preconditioning with electricity from a wall outlet than charging at a more expensive commercial charger.

Preconditioning while plugged in versus heating the cabin from the battery while driving can make a tremendous difference in cold-weather range.

In a short trip at 20 degrees F without preconditioning, range can fall 30% to 50% from the EPA projection on the window sticker, according to estimates in J1634.

Preconditioning while plugged in reduces the impact to 10% to 30%.

“Conditioning the vehicle before driving can play a significant role in vehicle range on short trip driving in cold weather (20%)," the presentation states with typical engineering understatement.

The effect of precondition will vary depending on vehicle technology, actual temperature and other factors, but preconditioning makes a big difference in all cases.

Other examples cited in an SAE presentation include a 10% reduction in range loss at 95 degrees F, from 25%-30% without preconditioning to 15%-20% after preconditioning.

The window sticker range estimates assume 72 degrees F. There’s some reduction at all other temperatures, but severe cold has the greatest effect, because heating a vehicle is most energy intensive.

“Educating customers about preconditioning is a huge factor” in EVs’ widespread adoption, Roos said. “EV range can be difficult to understand.”

New climate control techs boost range

Advances in battery technology, controls and other systems also are reducing the effect hot or cold weather will have on EV range, Roos said.

Supplier Valeo unveiled a couple of examples at the Shanghai auto show in China this week: a heat pump and heating panels hidden around the vehicle.

The heat pump “removes the need to choose between the travel range of the electric vehicle and the thermal comfort of the passengers," the supplier said.

It goes into production on an all-new EV platform from a European manufacturer this year.

The heat pump gets two-thirds of its energy from the ambient air, reducing its draw on the vehicle’s battery. It also uses a natural refrigerant, making the system a clean win on your Green New Deal bingo card.

Valeo predicts electric cars with the heat pump can travel up to 30% further at 5 degrees F than those fitted with conventional heating systems.

A second, elegant solution hides radiant heating panels behind the trim in places near vehicle occupants. It replaces the less efficient process of blowing heated air through the entire passenger compartment.

Called the Flex Heater, it uses 25% less electricity with four passengers on board — and 50% less when the driver is alone.

What happens to the battery when EVs sit for a month or more?

Most of us worry about cold weather causing batteries to die because our car wouldn’t start one frigid morning — or worse, on a snowy night at the airport, coming home from a week’s vacation.

That shouldn’t be an issue for EVs, in part because their high-energy batteries have a completely different chemistry from the old-fashioned 12-volt batteries that start conventional cars. EVs’ lithium-ion batteries are less likely to run down just sitting around than the lead-acid 12v battery.

Three automakers just getting into EVs in a big way agreed on that point, but their specific advice on what to do varied. That’s probably because no two companies’ battery chemistry and control electronics are identical, but also — somewhat unnervingly — because the technology’s new and automakers are still figuring out the answers themselves.

If your EV will sit for a few weeks in the winter, check your owner’s manual and online forums.

Until then, here are highlights of advice from GM, Ford and VW.

GM, from the Chevy Bolt manual:

— Do not plug in the charge cord.

— Remove the black negative (−) cable from the 12-volt battery and attach a trickle charger to the battery terminals or keep the 12-volt battery cables connected and trickle charge from the underw\hood remote positive (+) and negative (−) terminals.

Ford’s recommendation for its Mustang Mach-E:

When storing your vehicle for greater than 30 days, the state of charge should be approximately 50%. Additionally we recommend disconnecting the 12v battery, which will reduce system loads on the HV battery.

Volkswagen, maker of the new ID4:

— Trickle charge the 12-volt battery and store the vehicle with a state of charge that is high enough to make it through however long it will be sitting.

— Experiment to get a feeling for the rate of self discharge. Check it after a couple weeks and go from there to build confidence.

 

 

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