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Bolt EV DCFC charging test #6

10K views 38 replies 13 participants last post by  bro1999 
#1 · (Edited)
So I did another DCFC test with my Bolt. I tried to make sure the HV battery temp was up to where I thought it needed to be to max out the amperage right at the start of the session, but I couldn’t get it warmer than 60F before I got to the station.

Here are the numbers:
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

I noticed that the Bolt wouldn’t ramp up to the station’s max amp rating (125A) until the HV battery temp hit around 69/70F. I actually stopped the session for a few seconds and restarted it (when the battery temp was around 65), hoping when the session restarted I would hit the max 125A right out the gate, but the current stayed around 110-115A till the HV battery temp hit about 70F, which I then finally saw the 125A readings.

To summarize, I think the Bolt’s battery is pretty picky about temperature as far as unleashing the max charge rate of a charging station (at least 125A ones). In the spring/summer this likely isn’t an issue, but in the winter this is something one needs to keep in mind…especially if you are planning on fast charging after cold soaking overnight. I’m wondering if there is any way to make some hack so that we can gain access to the battery heater? Probably not. =/

I’m also curious if being at TOO low an SOC has any effect on max charging rates….anyone experienced 45+ kW rates when plugged in at a low <10% SOC?
 
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#2 ·
So I did the numbers in my head and it came out to an average charge rate of 40 kW. Not bad but not great. Is there any DCFC in the area that can charge at a advertised rate over 50 kW? I think the only one is in California, but I could be wrong. It will be very interesting to see what the Bolt can charge at if it is charging from a 75 kW charger, or better yet, a 100 kW charger. Maybe the latter would allow the charge rate to approach 80 kW.
I have to admit, though, that I am not fully up to speed on DCFC'ing. I just wish we could get real world charge rates up to 75 kW so that 30 minutes of charging would get you more than 2 hours of driving at 70 mph.

On edit: I find it interesting that BEV owners talk amp ratings and temps while amateurs like me talk kW charge rates.
 
#3 ·
Also, assuming the SOC-R values are accurate, I think we can conclude the bottom buffer of the Bolt's battery is 3-4%, and if that's true, the top buffer may also be 3-4%. So total overall capacity of the Bolt's battery is probably between 63-65 kWh.
 
#5 ·
Since the goal is to travel a distance, and how long you need to wait, miles per hour is probably a better litmus test than kW.
Doing the math in my head, that session was ~200 mph?
 
#8 ·
Here's a chart of my charge session.

View attachment 130545
Nice. So early posted mappings were just poor resolution by the system that provided the data hence the chunky curves. That's smooth, but appears that if it was allowed to exceed 125a, it would have continued to climb.

Do you know if the cooling fans were on yet? I assume that is °F.
 
#13 ·
Regarding battery temperature - didn't GM say they adopted a cell chemistry that "can" operate at higher temperatures than their earlier chemistries? Would that mean perhaps the cells' temperature/amp sweet-spot is higher than we are used to with the Volt and therefore really "need" to get warmer than GM's previous chemistries to optimize charge rate?
 
#32 ·
The charging power is being limited by the maximum 125a current of the existing CCS chargers at lower states of charge. You see the peak kw charge rate at 45-55% because the current can no longer rise but the charging voltage is gradually rising as the battery fills up. With future chargers that support more than 125a we will likely see the charging kW rate peak at a lower battery state of charge.
 
#33 ·
What you get from an 80 kW charger is a higher current limit. For today's charger's, the DCFC limits are 125 A and 500 V, there's some nuance around that, but practically speaking, I'm not aware of a station usable by the general public that exceeds those ratings, _yet_, as the future is tomorrow.

So there's a little bit of a ratings game - observe:
200 A * 400 V = 80 kW (near future)

125 A * 500 V = 62.5 kW (no common EV has a 500 V battery pack)
125 A * 400 V = 50 kW (Most EVs have charging voltages from 330 to 400 VDC depending on pack an SOC, some EV motorcycles have lower voltage packs - 200 V, etc.)

100 A * 500 V = 50 kW (Some chargers are rated like this, but it's practically a 40 kW charger, since EV packs are typically 400 V max.)

So the Bolt won't use the full 80 kW of an 80 kW rated as 200 A * 400 V charger. It will likely use the higher 200 A current limit for 5 to 20 minutes in the charge cycle depending on temperature as the pack warms up in the 30 to 50% SOC, then we should see it taper down from 200 A in the 50 to 65 % SOC region.

These are exciting times as we get the new products and discover what they can do. I just got my 2017 Bolt EV. My 2011 LEAF, when it was new was lucky to hit 42+ kW for more than a few minutes....
 
#34 ·
So the Bolt won't use the full 80 kW of an 80 kW rated as 200 A * 400 V charger. It will likely use the higher 200 A current limit for 5 to 20 minutes in the charge cycle depending on temperature as the pack warms up in the 30 to 50% SOC, then we should see it taper down from 200 A in the 50 to 65 % SOC region.
Can't wait until someone actually gets a chance to charge at a >125A charger to see how much power the Bolt will actually accept.

Are there even any >125A CCS chargers publicly available in North America yet? I read about a 150kW charger installed recently in Fremont, CA, but it's not open to the public -- only researchers.
 
#37 ·
What's interesting about this session is that it doesn't appear to be current limited. Most of the ones I've seen for the Bolt were, I think - power rising slowly as the pack voltage rises, until the car starts curtailing as the SoC rises. Yours appears to hit an initial high, then slowly fall - presumably meaning that something in the system is power limited - and the limit becomes more restrictive over time/heating?
 
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