Fast charging experience - Chevy Bolt EV Forum
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post #1 of 63 (permalink) Old 01-17-2019, 04:06 PM Thread Starter
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Question Fast charging experience

In November, I purchased a 2019 Bolt EV with DC fast charging capability and have just had my first experience using that feature. With outside temperatures in the 40's, I used a nearby EVgo fast charger for a half hour and according to a follow-up e-mail from EVgo, the energy charged was 11.6 kWh. From the Bolt's instrumentation, it appears that a half hour's DC fast charge added slightly more than a 1/8 increment to my battery charge level and extended the remaining range of my current charge by around 40 miles. For my future expectations, I am wondering whether that experience is pretty typical from the Forum's actual experience. Any input appreciated - thanks!
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post #2 of 63 (permalink) Old 01-17-2019, 04:21 PM
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Originally Posted by Ph63zink View Post
...With outside temperatures in the 40's, I used a nearby EVgo fast charger for a half hour and according to a follow-up e-mail from EVgo, the energy charged was 11.6 kWh. From the Bolt's instrumentation, it appears that a half hour's DC fast charge added slightly more than a 1/8 increment to my battery charge level and extended the remaining range of my current charge by around 40 miles...
Many things influence the amount of charge gained, three of which are:
1. How low is the charge when you plug in, and
2. Battery and/or outside air temperature
3. The rated charging capacity of the charging station.

You will experience a much higher rate of increase in the battery's capacity for a 1/2 hour charge if you plug in when the charge is down around the 1/4 mark on the green bar or lower than you will if the charge is already over half "full" when you plug in.

You will experience similar increases in rate of charge with temperatures that are warmer than 40 degrees.

If you were at an older EVgo station with a lower output capacity, the total charge received will be less than if you are at one of their newer installations where the output is, in some cases, considerably higher.
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post #3 of 63 (permalink) Old 01-17-2019, 04:27 PM Thread Starter
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Many thanks, NoMoPetrol, good information. I did not think to check the rating of the EVgo charger I was using. My Bolt had slightly under a 1/4 charge when I plugged into the DC fast charger. The half hour's worth of fast charging got the charge to around halfway between the 1/4 and 1/2 charge marks.
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post #4 of 63 (permalink) Old 01-17-2019, 04:30 PM
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What NoMoPe said, plus another one comes to my mind: some DCFC's have two plugs, attached to the same stall, which means you may have to share the output with another car. I remember I was charging at an EVgo from <50% SoC @ already feeble 32 kWh when comrade Leaf latched onto its Chademo on the other side, and dropped me down to 24 kWh.
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post #5 of 63 (permalink) Old 01-17-2019, 04:39 PM
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Ph63: For awhile, gather some data. Before hooking up, note the SoC (State of Charge) of the battery, the outside temperature, and the time. Sit in your car at the beginning of DCFC and note the initial "power" rate being accepted by the EV's battery. IF the station posts it (usually not on a placard, but in the display) note the Volts and the Amps. All DCFC power drops off in a hyperbolic fashion. The voltage usually stays the same while the amperage falls off.

Usually, if my initial SoC is <20%, I gain 80-90 miles in the 1st 30 minutes, 60-70 miles in the second half hour, 30-40 in the 3rd, and (once I have > 80% SoC) only about 10-15 miles in the 4th 30 minute segment. I only charged to full once (it was free, it was warm, and I was learning). It took a full 2 hours. My wife and I had a leisurely supper and walked around the college town for awhile. I was back at the EVSE for the last 30 minutes and, at shutoff, the amperage had dropped from 100 amps to 5 amps. It took a l-o-n-g time to put in those last 5 miles!! In travelling since then, I never charge to >80% SoC as the time spent is NOT worth the miles gained. I try to plan to arrive at the EVSE with <20% SoC.

While traveling, time is the essential feature. Many times I do NOT want to leave home with a "full tank". I calculate the distance, estimate battery consumption, allow for outside temperature, factor in what speed I can comfortably (& safely) drive, and add a "no-range-anxiety" factor. When we did the 230 miles single charge segment east to VA (noted above), I simply drove 60 mph on the Interstate and arrived with 23 miles remaining. When I go to Columbus (165 miles) on the way to Ann Arbor, I drive 65 mph most of the way and leave home with 75% SoC (45 kWh). If I find my estimated miles remaining (Guess-o-Meter = GoM) dropping below my "safety factor", or the mi/kWH staying below 3.5, I simply slow down bit. I have never had to get my knuckles white.

Good luck and keep us posted.
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post #6 of 63 (permalink) Old 01-17-2019, 06:44 PM
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Unless you absolutely need the range, there's very little need to DC fast charging if your battery is more than 65% to 75% full. At that point, you're really just "topping off." If you're traveling and want to maintain a decent speed, you'll generally want to start your charging sessions when your battery between 10% and 30%. At that point, how much energy and range you get back will depend on the speed of the charger.

The Bolt EV can charge faster than most of the chargers that are currently in service; however, faster chargers are coming online. At those faster chargers, you're typical stops will be 20 to 40 minutes, and you'll gain anywhere from 30% to 60% battery. Your range will depend a lot on your efficiency, but you could see anywhere from 50 to 150 miles of range added in a 20 to 40 minute session on those faster chargers.

Also, DCFC often charge fees based on time, so you might want to restrict your charging to under 55% (and definitely under 70%) because you will be getting the best bang for your buck that way.
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post #7 of 63 (permalink) Old 01-18-2019, 12:39 AM
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Unless you absolutely need the range, there's very little need to DC fast charging if your battery is more than 65% to 75% full. At that point, you're really just "topping off." If you're traveling and want to maintain a decent speed, you'll generally want to start your charging sessions when your battery between 10% and 30%. At that point, how much energy and range you get back will depend on the speed of the charger.
I agree, to a point. In CA (and near both coasts) DCFC is much more prevalent. If you are traveling from an adjacent state to/through WV (with NO CCS DCFC) it may well be that you drive 50-60 miles and then choose to DCFC because your destination is 225 miles further on. Unless you want to Level-2 charge for 2 hours, you may find yourself "charging early" to make the second leg a "non-stop flight"!
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post #8 of 63 (permalink) Old 01-18-2019, 01:24 AM
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I agree, to a point. In CA (and near both coasts) DCFC is much more prevalent. If you are traveling from an adjacent state to/through WV (with NO CCS DCFC) it may well be that you drive 50-60 miles and then choose to DCFC because your destination is 225 miles further on. Unless you want to Level-2 charge for 2 hours, you may find yourself "charging early" to make the second leg a "non-stop flight"!
Yup. I'd classify that as "absolutely need the range." After 95% battery, even when DCFC is available, I'm more likely to just use L2 or drive slower.
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post #9 of 63 (permalink) Old 01-18-2019, 05:20 AM
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Originally Posted by Ph63zink View Post
In November, I purchased a 2019 Bolt EV with DC fast charging capability and have just had my first experience using that feature. With outside temperatures in the 40's, I used a nearby EVgo fast charger for a half hour and according to a follow-up e-mail from EVgo, the energy charged was 11.6 kWh. From the Bolt's instrumentation, it appears that a half hour's DC fast charge added slightly more than a 1/8 increment to my battery charge level and extended the remaining range of my current charge by around 40 miles. For my future expectations, I am wondering whether that experience is pretty typical from the Forum's actual experience. Any input appreciated - thanks!
Quote:
Originally Posted by Ph63zink View Post
I did not think to check the rating of the EVgo charger I was using. My Bolt had slightly under a 1/4 charge when I plugged into the DC fast charger. The half hour's worth of fast charging got the charge to around halfway between the 1/4 and 1/2 charge marks.
Your experience isn't the typical experience, but it certainly has been experienced by others.

11.6 kWh in 30 minutes means a charging rate of about 23 kW. Gaining a bit over 1/8 of the battery means that the rate at which charge entered the battery averaged out to be about 16 kW. Either way, that's much less than half the charging rate the Bolt is capable of. So, let's talk about why this happens.

Although the car is capable of charging at 150A, but it will limit current based on battery temperature (and state of charge). We actually know a little about how it does that (source).

  • -30.0 ℃ / -22 ℉ — 0 amps, car will not charge at all until battery has warmed
  • -20.0 ℃ / -4 ℉ — 3 amps, very slow (1 kW, slower than home charging from a 120 volt outlet)
  • -10.0 ℃ / 14 ℉ — 12 amps, slow (4.3 kW, slower than typical level-2 home charging)
  • -0.0 ℃ / 32 ℉ — 30 amps (10.8 kW, finally faster than home charging)
  • 10.0 ℃ / 50 ℉ — 54 amps (19.4 kW)
  • 15.0 ℃ / 59 ℉ — 93 amps (33.4 kW)
  • 22.5 ℃ / 72.5 ℉ — 134 amps (48.2 kW)
  • 25.0 ℃ / 77 ℉ — 150 amps (54 kW, faster than almost all DCFC chargers can supply)
  • 40.0 ℃ / 104 ℉ — 150 amps (54 kW, faster than almost all DCFC chargers can supply)
  • 45.0 ℃ / 113 ℉ — 75 amps (27 kW)
  • 50.0 ℃ / 122 ℉ — 0 amps, car will not charge at all until battery has cooled

We can visualize this as the following graph:



Note, however, that (unlike the Leaf and the American edition of the upcoming Hyundai Kona, the Bolt can also heat its battery, but there is a lot of thermal mass to the battery, so it takes a while for the heater to raise the battery temperature). Thus, if you'd stayed longer, you'd have seen charging speed pick up a bit as the heater got the battery warmed up.

If we assume that the interpolation line I drew between the known points mirrors reality, at battery temperature of 45 ℉ you would have only charged at 46 amps (16.6 kW) initially. If your car had been sitting in the cold (e.g., overnight without being plugged in), it's possible that your battery was even colder.

On the other hand, driving the car warms the battery a little, and the battery has a significant thermal mass, so it's very possible for it to be 45 ℉ outside and have the battery be significantly warmer.

From your description, it seemed like you were using a DCFC charge as an experiment to test it out (and were disappointed).

In a more typical cold winter trip scenario, it'd go like this. You'd charge the car overnight while you slept. As part of the charging process after the battery is charged (which generates some heat all by itself), the car will automatically run the battery heater to raise the temperature closer to a good temperature. Before setting out, as you ate breakfast and got ready to leave, you'd use the preconditioning feature to warm the car up with wall power before setting out. One 30 minute session is great, two would ensure the car is as warmed up as can be. Preconditioning will further make sure that the battery is brought up to a good temperature.

During the trip, a mix of the thermal mass of the battery retaining the heat from preconditioning and the heat generated from using the battery will keep it at a good temperature so that when you arrive at your first charging stop you'll be well placed to charge at a good rate. The charging process will further raise the battery temperature so that further driving and charging will always see good speed.

Put simply, EV batteries don't like the cold. There are things you can do to help, but it's also possible to be caught out. It's true for all EVs. There are frustrated folks on Tesla forums, too, for example.
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post #10 of 63 (permalink) Old 01-18-2019, 11:38 AM
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Great post, @Vertiformed . It should be required reading for anyone getting an EV with DCFC capabilities.

Like @Ph63zink , I was also very disappointed with my first (and only) DCFC. It was about a month after I bought the Bolt. The temperature was hovering around freezing. I had just left my destination on my way home, so the battery was still cold. And my SOC was around 50%. I committed just about every DCFC mistake you could make. On the good side, researching why my charging rate was so bad led me to this forum.
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