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As I was reading this thread...

I was thinking about what I observed with the 100kW charger a year ago....

And now that I have observed quite a few 150A charging sessions at a 100-200kW chargers since then I have formed some thoughts on the matter, which is this:

The thermal design of Bolt has been optimized for 150A maximum charging speed.

According to my observations, the 2017-2019 Bolts are able to charge at maximum speed, up to 150A, without any heating or cooling when the battery is between 22C (72F) and 32C (90F). A rise of 10C is easily possible in about 30 minutes of an optimal DCFC session, and once it goes over 32C the cooling circulation kicks in.

If I'm charging with about 10 to 20% battery left, this threshold is reached around 50 to 60% SoC, and as many of you know this is where the first taper to 100A occurs. Due to the lowered charging speed, the temperature plateaus for a while, but on a moderately warm day it eventually leads to the cooling being activated for a short time until the charging speed drops to 65A at around 67%.

Had the Bolt been allowed to charge faster, to, say, 175A like Kona/Niro or even 200A, I could see the cooling system being activated earlier and much more frequently. Also, the faster charging speed might not be sustainable for a reasonable duration due to the limits of the cooling capacity. It would be reasonable to assume, then, that the GM engineers struck a balance between what little gain the faster charging speed might provide against the design constraints of the vehicle.
 

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Charging from 10% to 80% takes 50 minutes in the Kona and 55 minutes in the Bolt based on these videos:


The Kona has a slightly larger battery at 64 kWh compared to 60 kWh for the 2017-2019 Bolt but given that the 2020 Bolt has a 66 kWh battery and charges a bit faster from 10-80%, it looks to me like the charging times of the Kona and 2020 Bolt are about the same.

Mike
 

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extrapolating the video's data for a 10% to 70% more typical charge:
2017-2019 Bolt = 46-47 minutes <— edit, bad math, ignore this post
2019 Kona = 38-39 minutes

8 minutes per charging stop. That's significant enough IMO on road trips. 1/2 hour (ish) on a 500 mile trip?
Not a deal breaker, but definitely nice.
 

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The thermal design of Bolt has been optimized for 150A maximum charging speed.

***

Had the Bolt been allowed to charge faster, to, say, 175A like Kona/Niro or even 200A, I could see the cooling system being activated earlier and much more frequently. Also, the faster charging speed might not be sustainable for a reasonable duration due to the limits of the cooling capacity. It would be reasonable to assume, then, that the GM engineers struck a balance between what little gain the faster charging speed might provide against the design constraints of the vehicle.
First, I think it's important to distinguish between the Bolt EV's "thermal design" and its battery conditioning system's software parameters. The software parameters certainly are optimized for a 150 A maximum charging speed because the Bolt EV cannot or will not draw additional power beyond that 150 A threshold from the charger for battery conditioning. That means that any battery conditioning that takes place reduces the amount of energy going into the battery. The Bolt EV does its best to not reduce charging speed in order to condition the battery, but it will do so after certain thresholds have been reached (as you noted, after the battery reaches 32 C).

Second, my point in calling out the 150 A cap on the power draw is not only that additional power might be available for charging (likely a true 1 C charging rate of ~170 A in the 2017-2019 MY Bolt EVs and ~190 A in the 2020 MY Bolt EV) but also that additional power would be available to run battery conditioning throughout the entire charging curve. That means that the Bolt EV's battery conditioning software parameters could be much more aggressive without ever affecting the charging rate. In essence, the Bolt EV's thermal management would be better able to cool with 170 A charging because the AC system could be cooling the battery the entire time without impacting the 60 kW maximum charging speed.
 

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He is saying that the theoretical max charge is. The Bolt's battery should be able to charge at 1c, which would be 60 and 66 kW for 2019 and older and 2020 respectively. Of course, 1c max charging is starting to become less a rule, but the Bolt battery is unlikely to be able to be safely pushed much past 1c charge rate.

So if there were a 200 amp charging port and wiring, in theory you could charge at 60-66 kW, run the battery cooler as fast as needed to have a more aggressive charge curve (higher charge longer), and run the cabin HVAC without decreasing the charge rate of the battery.
 

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Yes, so you shouldn't just look at the charging speed increase because there are additional benefits. I agree that a simple 5 kW increase to the charging speed wouldn't be worth much, but there are more benefits to be had.
 

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extrapolating the video's data for a 10% to 70% more typical charge:
2017-2019 Bolt = 46-47 minutes
2019 Kona = 38-39 minutes

8 minutes per charging stop. That's significant enough IMO on road trips. 1/2 hour (ish) on a 500 mile trip?
Not a deal breaker, but definitely nice.
I get 38 minutes from 10-70% for both. The Kona video shows 38 minutes so that part is easy. For the Bolt, it takes 28 minutes to charge from 0-56% so to charge from 10-56% should take about 28*(46/56) or 23 minutes. Then another 15 minutes to charge from 56% to 70%. 23+15=38%.

Mike
 

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extrapolating the video's data for a 10% to 70% more typical charge:
2017-2019 Bolt = 46-47 minutes
2019 Kona = 38-39 minutes

8 minutes per charging stop. That's significant enough IMO on road trips. 1/2 hour (ish) on a 500 mile trip?
Not a deal breaker, but definitely nice.
There has to be at least one typo above (or I just don't understand.

The most confusing is "8 minutes per charging stop" What?

Then : "1/2 hour (ish) on a 500 mile trip". The Bolt has a 240-250 EPA range, and that is less on the freeway. So that is a minimum of two stops. And, unless you are Evel Knievel (yup, I am that old) you aren't going to want to arrive with only 10 miles of range. So, full battery at start, 180-200 miles to first DCFC (charge to 75%, adding about 40 kWh so about 60-70 minutes), 120-150 miles to next DCFC (charge to 75%, another hour), drive 120-150 miles, almost there but you want a safety buffer so ... third DCFC (charge to whatever floats your boat, also depends on overnight charging situation at destination). That is over 2 hours of charge.
 

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I get 38 minutes from 10-70% for both. The Kona video shows 38 minutes so that part is easy. For the Bolt, it takes 28 minutes to charge from 0-56% so to charge from 10-56% should take about 28*(46/56) or 23 minutes. Then another 15 minutes to charge from 56% to 70%. 23+15=38%.

Mike
I obviously screwed up my math. Sorry about that guys, just disregard my first post. No idea what I was looking at. Since it shows it takes 43 minutes to go from 0-70%, how did I get 46 minutes for 10-70%. doh! (n)
 
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