For a few years now, Tesla has shown what a nationwide network of DC fast-charging sites for long-range electric cars should look like.
Its Supercharger network now covers virtually all of the lower 48 states, and until earlier this year, it was completely free to Tesla drivers.
The Chevrolet Bolt EV, the first affordable battery-electric car with 200-plus miles of rated range, also offers DC fast charging as an option.
But Bolt EV fast charging is less capable than Tesla's in three crucial ways.
First, there's no coherent network of charging sites despite using the Combined Charging Standard (CCS) protocol adopted by every German maker and every U.S. carmaker except Tesla.
CCS is heavily supported, but no overall body chooses installation sites for charging stations to provide a unified, coherent network.
BMW i3 and Volkswagen e-Golf electric cars using Combined Charging System (CCS) DC fast charging
The first phase of the Volkswagen "Electrify America" plan may apparently have to substitute for that.
It is part of VW Group's 10-year, $2 billion program for zero-emission vehicle infrastructure, which it agreed to fund in settlements resulting from its diesel emission scandal.
Second, while Chevy says the Bolt EV can charge at "up to 80 kilowatts," that's both lower than the 135-kw maximum for a Tesla and effectively capped at the 50-kw rate of all currently deployed CCS charging stations in the U.S.
Third—and the topic of this article—is that the Bolt EV starts to taper its charging rate fairly early in the curve, as we experienced two weeks ago.
That means that when you plug in a Bolt EV with 50 percent of capacity or more remaining in its battery, the fast charging rate may not be even 50 kw.
While charging rates taper off over the last 20 percent of battery capacity in virtually every electric car, the Bolt EV appears to start the taper much earlier and gently ramp down charging far earlier than the 80-percent level.
2017 Chevrolet Bolt EV electric car at EVgo fast-charging station, Newport Centre, Jersey City, NJ
This may be good for battery longevity, an area in which GM's Chevrolet Volt plug-in hybrids appear to excel, but it doesn't help owners on certain types of long trips.
The behavior has now been carefully described by a Chevy Bolt EV driver known as "Bro1999," who blogged about it roughly a month ago after receiving his 238-mile electric car in Maryland.
As of that time, he had fast-charged the Bolt EV five times at both EVgo and ChargePoint sites.
It's worth reading the entire post, but his observations include:
- The maximum charging rate he saw was 46 kw on a 125-amp charger;
- The Bolt EV battery is quite sensitive to internal temperature, and needs to be at 65 to 70 degrees F to charge at the highest rate;
- Fast-charging starts to taper off at 50 percent capacity, and tapers again at 70 percent; and
- Chevy's advertised "90 miles in 30 minutes" will only likely occur if the battery starts between 0 and 50 percent capacity.
DC fast-charging behavior of 2017 Chevrolet Bolt EV electric car [chart by Bro1999]
In addition, our reader Lang Reynolds passed along the following comments, on Bolt charging at EVgo fast chargers, received from an electric-car driver with industry-insider knowledge:
The EVgo deployed network is all 50-kw, and if a fully operational (i.e. not mechanically impaired) charger delivers a slower rate than that, it’s because the car is ‘asking’ for less (either because of the ambient temperature, or because of the car’s battery state of charge).
We’ve seen this complaint on Chevy Bolt forums and threads. It seems from those that [Chevrolet has] got the car set to throttle down on charge rate a lot sooner in the charge curve than most people expected them to.
GM was pretty careful to advertise their charge rate as an “up to” and “under ideal conditions” thing, so it’s a bit of selective reading [to create] rosy expectations in the customers as well.