Driving Electric in the Cold

Last weekend, extreme cold weather caught Chicago ride share operators unprepared for driving their electric vehicles in the extreme cold. In most cases, these operators were renting vehicles through the ride sharing services with which they were affiliated. Tesla Model 3, Kia Niro, and Chevy Bolt were the most common choices, and all vehicle types found themselves dead in the water at a charge point.

In this article, I’ll identify cold weather effects on battery electric vehicle operation and describe how the practice of scant bunkering can reduce time spent charging on shift and reduce charge point congestion.

Revisions

1. 2024-01-20 Original

References

1. Driving Tesla Model Y in Cold Weather

A Hypothesis

Experienced EV drivers believe that the ride share operators were following normal ICE taxi operating practices. That is, they were trying to fully charge their electric vehicle between shifts as they would an ICE taxi. If they needed more energy on shift, they were likely trying to charge to full also. That’s normal ICE vehicle fuel management. This had several consequences during extreme cold weather.

• Battery electric vehicles take longer to charge in the cold. Charge times can easily double when the battery is cold.
• The first half of a charge to full takes less time than the second half. Charging from 80% to 100% often takes as long or longer than charging to 80%.
• This characteristic of charge rate versus charge level suggests that scant bunkering can be beneficial in reducing shift time spent charging.
• Vehicles arrived faster than the charge point could service those already there. The backlog queue grew.
• The wait was long enough that vehicles exhausted their batteries while in the queue.

The following conditions and choices aggravated the charging experience.

• If the battery is too cold, the vehicle will not charge until it has warmed up the battery to a temperature above freezing.
• Cold batteries charge slowly until warm (86-98 degrees F).
• The size of the ride share electric fleet was large enough to oversubscribe Chicago’s DC fast charging points.
• Drivers were likely unaware how much extreme cold weather would reduce charging rates.
• Drivers were likely unaware of the extent to which charging rate slowed as the battery filled.
• Drivers were likely unaware of the magnitude of the range degradation and charging rate degradation that they would experience in extreme cold.

Scant Bunkering

Drivers were likely unaware of the benefits of scant bunkering. Scant bunkering is the practice of charging to the extent needed to complete a trip leg vice filling the battery to an arbitrary level (80 to 100 percent). Scant bunkering significantly reduces the time lost to charging on a voyage.

Ride Share Recommended Charging Practice

I own two battery electric vehicles, an ID.4 currently undergoing mishap repair and a Tesla Model Y. My practice is to charge my vehicles at home on a Level 2 charger in line with Tesla and VW recommendations. I leave the vehicles on the charger, and I use scheduled departure preconditioning. I charge the Tesla daily to complete both the preconditioning and the charging on the over-night base rate from my utility.

Both Tesla and VW have similar recommendations. Below, I describe how ride share operators may take advantage of recommended practice to be highly available during cold weather operation.

• Do pre-shift charging using Level 2 charging. Reserve DC Fast charging for maintaining operating reserves during the shift.
• Charge the vehicle to 80% capacity for shift start. Recommended full charge level is dependent on battery chemistry. Some Lithium Iron Phosphate batteries may be charged fully each day. See your owner’s manual for your Model and VIN.
• Keep the vehicle on the level 2 charger overnight. This allows the vehicle to maintain battery temperature.
• A preconditioned vehicle is more efficient than a cold one. Use scheduled departure preconditioning to warm the battery for operation using shore power from your Level 2 charger. A Level 1 120 VAC charger may not be able to deliver enough power for preconditioning on shore power. Some battery energy will be used for preconditioning.
• Use scant bunkering to minimize time spent charging as described herein. Keep enough charge on hand to take a couple of fares, then move on. Keep charge between scant level and bingo level.
• Use the car’s internal navigation to navigate to fare pick-up, fare destination, and to your marshal location to await the next fare. This enables the navigator’s bingo logic to take you to a charger when the need arises.
• Keep a high bingo level during extreme cold. In the cold, reserve 20-25 percent to travel to and wait for a charge point.
• Navigate to the charge point. A Tesla will automatically initiate preconditioning when navigating to a SuperCharger.
• Charge for 15 to 30 minutes. Normally, this will add 150 miles or so of range. In the cold, maybe half that. Bring on enough bunkers for two fares.
• Don’t sit on the charger. Others need it. Once you have your take aboard for a couple of fares, move on.
• Convince your mates to follow scant bunkering practices as described here.

Commuter Recommended Charging Practice

Most commuters travel 30 or so miles per day — this is the median national round-trip commute. Median — half of you may have longer daily orbits. If your daily orbit is less than 30 miles or so, you can maintain charge using a 120VAC 12 Amp Level 1 charger. If your daily trip is longer, you’ll need to start the week full, recharge daily, and top off on the weekend or when the car reaches bingo. But you can basically follow the ride share operator guidelines above.

• Charge a little bit each day allowing the car to precondition and complete the charge on cold days.
• On cold days, precondition the vehicle before departure.
• Charge at work if you can.
• Top off using the DC fast charger when you reach your personal bingo level. I use 20% as bingo.
• Navigate using car navigation between work and home. In a Tesla, this enables bingo monitoring and routing to a SuperCharger when bingo is reached. Waze can’t do bingo!

Bingo and Scant Buffering Explained

Bingo is an aviation term of art for the fuel level at which the aircraft must immediately proceed to a fueling point and take on fuel (bunkers). Reaching bingo typically means that the aircraft must divert to a planned alternate destination having proper fuel and fueling equipment, land, and take on bunkers (fuel).

I’m a former nuclear submariner so bingo and bunkers are somewhat foreign notions when you serve on a vehicle that comes with fuel for life. But I’ve worked with military aviators over the years and have picked up some of the lingo.

A former F-15 Eagle pilot and Delta Airlines command pilot introduced me to scant bunkering in commercial flight operations. Schlepping a plane full of gas to flight level takes a lot of energy so commercial pilots carry just the fuel they need to reach those airports where gas is cheap. Clever!

Ride share operators can do the same to minimize time fueling while on shift. Carry enough energy for a couple of fares or until a planned work break. Recharge while on break bunkering sufficient fuel for a couple of fares or to reach the next break.

Tesla lets you set a bingo level on the navigation settings page. When the car’s energy level reaches bingo, the car will insert a trip waypoint to divert to the nearest Tesla SuperCharger for recharging. Set up the car’s navigation for each leg of your trip and have a bingo level entered in your car’s navigation settings. Other makes may have a similar feature.

On our trip to James River Greyhounds Picnic in Richmond, I unintentionally tested this feature by inserting the planned mid-trip refueling stop at the end of the voyage. The car called bingo, led me to the SuperCharger, and promptly got lost in the car park. Fortunately, it took me to an entrance from which the charge point was visible, and I could follow my nose to it.