Friday, March 3, 2017

Fast charging experiences with the Bolt

Wow, it's been forever and a day since my last blog post! Turns out the blog update frequency tanks once the object you've been obsessively blogging about ends up in your possession! 😋

So after almost 2 months over ownership and 2,000 miles on the road, I've also managed to use CCS DCFC fast charging stations several times (once out of necessity, the other times purely for testing purposes). What I've found is that, like with EV range, your mileage will vary when fast charging the Bolt....literally.

The Bolt is outfitted with a SAE Combo Charging System (CCS) charging port, so it can only fast charge at locations with CCS plugs. It cannot use CHAdeMO plugs that Japanese vehicles such as the Leaf can use. While CHAdeMO stations vastly outnumbered CCS-compatible stations a few years ago, the gap is closing as the number of CCS fast charging stations is increasing every day. Most new non-Tesla DC fast charging stations have both CHAdeMO and CCS plugs.

In my area (Howard County, MD) there is a fairly decent CCS-compatible fast charging network. There are over 60 CCS stations within 100 miles of where I live, so I can pretty much drive anywhere in Maryland without having to worry about range. Hell, the Bolt's 238 (more like 190-200 miles in sub-freezing temperatures) mile EPA range is usually more than enough for my family without even factoring in fast charging capability!

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Not too shabby a network!

While there are several companies that offer fast charging stations, the main 2 in my area (and pretty much across the country) are Chargepoint and EVgo. Both currently have fast charging stations that advertise 50 kW charging rates. As we will see a little later, 50 kW advertised does not equal 50 kW observed in real-life charging. The Chargepoint stations in my area (mostly installed at Royal Farms locations) cost 29 cents/kWh, with a $3.50 minimum charge. EVgo charging prices vary by the plan you choose, but the best plan for people charging multiple times a month is its "On The Go" plan, which costs a flat $14.95/month and 10 cents/min while fast charging. Again, these are Maryland rates, so if you live in another region the pricing will vary.

While GM has been coy with the 2017 Bolt's exact fast charging capabilities, it has stated that the Bolt can achieve "about 90 miles in 30 minutes", presumably based off the official 238 EPA-rated range. There is some fine print stating charging performance is dependent on factors such as ambient temperatures.

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90 miles in 30 minutes *HUGE ASTERISK*

Having experienced at least 6 separate instances of fast charging at various Chargepoint and EVgo stations in my area, here are my findings:

  • No one will actually see 50 kW charge rates at a 50 kW fast charging station with a Bolt...at least not a a station rated at a maximum 125 amps. 46 kW has been the fastest rate I have observed. I DO believe the Bolt can charge faster than 50 kW if hooked up to a fast charging station rated higher than 50 kW/125 amps. Too bad none exist yet that are available to the public.
  • The Bolt's battery is pretty sensitive to temperatures when it comes to fast charging. With data logged by my OBDII reader and Torque Pro app, I've noticed that I don't experience max (125 amps) charge rates until the Bolt's HV battery temperature is between 65-70 degrees F. If you are planning on fast charging first thing in the morning after parking your Bolt outside in sub-freezing weather unplugged, you will likely experience throttled charge rates till the battery comes up to temp.
  • The Bolt tapers the max charge rate fairly early compared to say the Spark EV. While Spark EV owners reported near 50 kW rates from 0% to almost 80% SOC, I've noticed the Bolt starts tapering rates at around 50% SOC (ramps down to ~38kW/~100 amps) and again at 70% (down to ~24 kW/~60 amps) from peak ~46 kW/125 amp charge rates at a 125A station. At a little over 80%, the rate again tapers down to <20 kW and stays there till fully charged.
  • The ~0-50% SOC window is where you will see the Bolt charge at the advertised "about 90 miles in about 30 minutes" rates, assuming the HV battery is up to temperature. In the spring/summer/fall, battery temps shouldn't be an issue, but in winter areas that routinely see sub-freezing temperatures, this is something to be aware of.
  • The most I ever saw in a 30 minute session was 21.84 kWh charged at a 125A EVgo station. Translated in EPA-rated miles, that's ~87 miles in 30 minutes. Slight throttling was experienced.
The below chart might be an info overload, but you can see that the max charge rates (125A/46 kW) aren't realized until the HV battery temp reaches around 70F. 

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2 minute gap as I started the charge session

And the charging figures:

Session start time: 5:27AM
HV battery SOC% (SOC-R value in Torque Pro): 9.02%
Battery SOC% according to the station: 5%
HV battery temp: 60.8F
Ambient temp: 57F

Session end time: 6:08AM
HV battery SOC% (SOC-R value in Torque Pro): 50.2%
Battery SOC% according to the station: 47%
HV battery temp: 77F
Ambient temp: 57F

Total kWh charged: 26.73 kWh (according to Torque Pro) / 27.6 according station
Total time charging: 39 minutes (2 minute gap when stopping/restarting charging)
Total SOC% gained: 41% (according to Torque Pro) / 42% according to station
Max charge rate observed according to car: 46 kW

Once a >125amp CCS station is online, I am eager to see just how much power the Bolt can suck in! If amperage exceeds 131A, a guy I know owes me 100 bucks. 😎

7 comments:

  1. I wish you compared to old Leaf than SparkEV. It makes Bolt sound worse than it really is.

    Troubling thing is that the current doesn't reach peak of 125A until about 30%. That means even with much higher powered charger, peak power would only occur between 30% and 50%. It may not be much more than 50 kW at such short window.

    I don't know what the issue is. I had high hopes that Bolt would be able to charge at 3X SparkEV power to 80%. Current setup is worse than even the new Leaf in terms of percentage. I hope GM will "fix" it after more powerful chargers come on line.

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  2. GM apparently developed a new, unique nickel rich battery chemistry for the Bolt to get the weight down (and cost?). I wonder if it is really capable of faster charging? It is curious that in reprints I have seen of the owner's manual it states that a DCFC should have an 80KW rating. Looking for chargers between Florida, Georgia and NC I have not run across one yet. Because of the charge rate throttling after 50% SOC it seems like it would not help much at all in any case. I can tell you that my Model S60 charges at a max of about 92KW (at 120KW Superchargers) or about 300 Rated Miles/hr up to around 50% SOC. After that it tapers down to around 42 KW. But the S60 battery is really a software limited 75 so not really comparable.

    I am curious about the actual range you experience at different speeds. After delivery did your range ever show the rated 238? What is the miles consumption at 70mph? 75mph? 80mph? I can tell you that my Model S burns RMs at about a 5% premium at 70mph, 15% more at 75mph, 20% more at 78mph and 25% more at 80mph.

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  3. This battery is using more active material in the same cell structure for higher energy density. But as a result, the power density is less: discharge at circa 2C, and charge at 1C. So it's likely to take 60' to charge from 0 to 80%, even with an 80kW charger.

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  4. I would be interested to see the taper in the charging amperage from 50% to 90% SOC. I did something similar for our e-Golf. You can see the results here:
    http://www.myvwegolf.com/forum/viewtopic.php?f=12&t=444&start=11

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  5. Really useful information. Great work.
    Tim Hoff

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  6. Looks like the Bolt will accept at least 150 amp at 40% SOC...

    I'd suspect there's at least one more step in there though.

    http://www.hybridcars.com/chevy-bolt-ev-can-charge-at-55-kw/

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  7. can you post the pack voltage at full 100% dc fast charge, and then the voltage at 100% overnight slow charging? Just curious. thanks!

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