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Maximum charge rate of 55 kW when conditions are right

36K views 20 replies 10 participants last post by  GJETSON  
#1 ·
I've seen a few posts claiming the best/fastest charge capacity at Level-3 DC chargers on a 2017-2022 Bolt is 55 kW. This is welcome information, but i tried over an hour to get such answers from Chevy's customer service departments. I'm glad to know what to expect as a best-case scenario maximum, so thank you everyone who posted that basic info, that figure.
I assume this max of 55 kW is true even with a new (post-recall install) battery that's placed in a 2020 Bolt during the calendar year of 2023? In other words, is it true that Chevy is ~not~ installing batteries or related infrastructure in vehicles to allow 100 kW of charging at a 150 kW or 350 kW public DC charging station?
 
#2 ·
I assume this max of 55 kW is true even with a new (post-recall install) battery that's placed in a 2020 Bolt during the calendar year of 2023? In other words, is it true that Chevy is ~not~ installing batteries or related infrastructure in vehicles to allow 100 kW of charging at a 150 kW or 350 kW public DC charging station?
Bolt so far isn't going above 55 kW DC FC rate. You want faster? Get a different vehicle. Other (w/newer designs) GM BEVs can DC FC faster.

I haven't watched most of
but he starts charging that vehicle at ~1:40.
 
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#3 ·
For all that the Bolt gets dinged for its slow “fast charge” rate, it is an old design, perhaps built without enough foresight. Heck, they didn’t even make DC fast charging a standard feature. Just out of curiosity I tried to find out what the DCFC structure looked like in 2017 and I ran across this: EVgo Opens its 1000th DC Fast Charger. The press release details how the charging stations are rated at 50 kilowatts. My how times have changed, and how the Bolt has not. I suppose if they hadn’t headed off toward Ultium, and there hadn’t been the recall debacle, maybe Bolts might have gotten some improvement, but I suspect that simply was not possible without a complete redesign. Still, for the money it is hard to beat. I’m not complaining.
 
#4 · (Edited)
FWIW, when Bolt came out in Dec 2016, it was probably the fastest non-Tesla BEV for DC FCing in the US. It is super unfortunate that GM did nothing to improve it over the years, but I'm unclear how much of the bottleneck is the cells themselves vs. the other parts (e.g. wiring, inlet, etc.) vs. GM and/or LG being (too?) conservative.

I know some folks have cited cooling as being a bottleneck, but I don't buy that as an explanation for the taper at ~50% SoC. If's not like the AC compressor sounds loudly when you reach that point. You can start at 55% with a not hot battery and it's not going to DC charge fast.

BTW, if you look at the 2016 US sales charts from Monthly Plug-In EV Sales Scorecard: Historical Charts, the non-Tesla DC FC-capable BEVs in shipping/shipped in the US at the time:
  • CHAdeMO - Leaf, Soul EV, i-MiEV
  • CCS1 - i3, Bolt EV, Spark EV, e-Golf, Focus Electric gen 2 might've gone on sale in late 2016 (gen 1 had no DC FC capability)

I don't know off-hand about gen 2 FFE, but the rest don't DC FC real fast either.
 
#5 ·
I assume this max of 55 kW is true even with a new (post-recall install) battery that's placed in a 2020 Bolt during the calendar year of 2023? In other words, is it true that Chevy is ~not~ installing batteries or related infrastructure in vehicles to allow 100 kW of charging at a 150 kW or 350 kW public DC charging station?
Correct. It's likely that the battery cells both old and new can take in more than 55kW charge rate, but GM decided to limit it anyway due to some reason - be it wiring, cooling, etc. - although the specifics were never officially disclosed. I say it's likely for two reasons - one, it can actually take in up to 70kW for a brief period of time during maximum regenerative braking with the regen paddle. Two, batteries of similar chemistry supplied by the same manufacturer to a competing EV - Hyundai Kona - can be charged up to 77kW.
 
#7 ·
Agreed, the cells should be fine. The chemistry is apparently ok with 1C charge/discharge rate, probably even a little higher. The C-rate on batteries is the average full charge/discharge rate over an hour. In my experience, charging from 20-98% takes around 2 hours on DCFC (I have had to do this on 3 occasions). That the 65kWh pack takes over 2 hours to charge 0-100% implies a charging C-rate of less than .5. As a reminder, a 1C charging rate would take just over 1 hour to charge the 65kWh pack to 100%.

From the 55kWh performance, and knowing pack voltage, it is clear 150A is the limiting factor. This is either wiring or DCFC port, and obviously could be improved given other EVs like Kona and Niro with apparently similar battery chemistry and pack size. However, as I understand, pack cooling is perhaps a limiting factor, that faster charging would generate more heat than the cooling system can mitigate. Heat is the factor that leads to cell damage, so OEMs have to consider pack reliability and lifetime when setting BMS parameters, and GM apparently went conservative here.

My conclusion is the system was designed around what was state of the art in 2014 when engineering was finishing design work on the Bolt. At 55kW, the cooling is probably adequate, but would be unable to keep temps tolerable at faster charge rates. By that late in the dev cycle, it was probably too late to redesign the pack cooling so they stuck with what they had. I also suspect Ultium design work started shortly after the 2017 Bolt went to market, and the decision was made by then that the BEV2 platform the Bolt is based on would be discontinued. With no funding to improve the pack design, any effort to improve wiring was off the table.

I haven't seen much on the charging curves of Lyriq or Hummer. We do know peak charging speeds of ~350kW (Hummer) and ~190kW (Lyriq) are being observed. But Hummer's 800V pack requires 800V DCFC units to achieve peak charging speeds.

As I understand, Lyriq's pack is ~100kWh, so a 1C charge rate would mean about 100 minutes 0-100%. LR Blazer and Equinox will probably share this pack size. I suspect it is a little better, the few references I have seen suggest 30-90% in 45 minutes. Most references I have seen suggest the tapering starts a bit later, 65% instead of 50% on the Bolt, and holds a respectable charge rate up to 80% or higher.

OK, now for a little speculation... We do know, thermal management was a big effort in Ultium development. GM has shared that they are engineering heat pumps and heat recovery systems into the platform. I think it is probably safe to guess they will be somewhat conservative though, maybe boosting charging speeds after some time to learn how real world experience relates to pack health? Most likely, any tweaks would be in the form of charging curves, the peak charge rates are probably set by architecture, but the curve might be allowed to tolerate higher amps longer into the session if heat isn't a problem in real world experience.
 
#6 ·
It's the maximum power the car will request from the charger. The earlier-generation batteries in the Bolt probably aren't rated for more than a 1C charge rate. The native capacity is probably about 70kWh with 65kWh usable - which is probably why regenerative braking is limited to 70kW.

The new Ultium platform uses high-rate cells that can be charged or discharged at a much higher rate.
 
#11 ·
A C-rate of 1 is simply the rate equaling the capacity in Amp-hours. For a 200 Amp-hour battery, the 1C rate is 200 Amps. That will discharge the battery in less than one hour, and it will take more than one hour to charge. C rate is not determined by charge or discharge time.

The capacity is usually given at a fractional discharge rate... so a "200 Amp Hour" battery will be given that specification at a lower discharge rate, such as C/10 or C/20. C/20 was common for lead acid and Nickel chemistries. So you only get the 200 amp hour capacity if you discharge at C/20 or 10 Amps.

Battery marketing is deliberately confusing :D
 
#13 ·
I was asked a question about the new battery DC charge rate yesterday.


The high today was 72 F here. The last time it was this warm was the 12th of November. The car was down to 30% SoC by the time shopping, and recycling were done, so I figured I'd try to warm the battery up by flooring it from 40 mph to 55 mph, and regening back to 40 mph. It would still pull 140 kW at this low SoC, and hit 70 kW on regen. This, and getting on the interstate up to the Sheetz, warmed the battery up a degree or so.

I pulled in at 25.1% SoC to the EA "150 kW" charger. The pack was at 66.2 F. The charge started at 43.9 kW, per Torque Pro. The battery heater started up, and gradually raised the battery temperature.

I turned the car on, and ran the HVAC on Hi/90F. The charger jumped to 49.2 kw, but the amperage into the battery actually dropped from 126.4 A to 118.2 A. The rest going to the heater, AC, and 12 volt charger. I turned the car off, and charge rate dropped again. The highest I saw during the rest of the charge to 51% SoC, was 44.7 kw.

The battery reached 77 F before the heater turned off. The pump kept running, and the battery reached 80 F, by the time I quit. Clearly, our Bolt won't reach 55 kW charging now, unless the battery is 80 F when we arrive, if then. That will have to wait for warmer weather to test.

.
 
#14 ·
Your result is interesting, but as a counter to it, I charged last May in Flagstaff, AZ with my new battery. High temp that day was ~70F. I had driven 160 miles from Phoenix (75mph up a 6000ft climb) and ate lunch for about 90 minutes before heading to the charger. This was the charge curve I recorded then. Car was off the whole time I charged.
Image
 
#20 · (Edited)
I am a bit puzzled about the specs on the Bolt for charging. If the Bolt is truly limited to 150 amps, and 55 kW, for charging, then the charge curve doesn't make sense. The charge curve is supposed to start dropping by 50% SoC, yet the pack is at ~350 volts at 50% SoC.



55 kW = 55,000 watts

55,000 watts ÷ 150 amps = 366.666 volts

I am almost certain the charger isn't putting out 366 volts at 50% SoC.

[edit] I went back through some of my old Torque Pro screen shots, and see that the charge voltage could indeed be 16 volts above the resting pack voltage.