[bro1999]

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?

 

[Ziv]

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.

 

[bro1999]

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.

 

[Neromanceres]

Keep in mind at very low SOC the charge voltage will be lower. So even if you were drawing 125A your charge rate likely wouldn't be much more than 40KW.

 

[Qinsp]

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?

 

[Ziv]

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?

I get around 4.2-4.6 miles per kWh at highway speeds of 63-67 mph, so I would figure about 180. But I drive a Volt (and I tend to drive slower than some) which is a bit slicker than a Bolt. Not sure what miles per kWh is for a Bolt.

 

[bro1999]

Here's a chart of my charge session.

 

[Qinsp]

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.

 

[bro1999]

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.

Nope, TMS didn't come on at all. And yes, temps are F.

The spikes in the amperage in the first part of the charge session were me turning on and off the HVAC system. It seems if the amperage is under 110 or so and you turn the HVAC on, the Bolt will request the station pump out more power to use for HVAC systems. Charge rate initially dips, but then recovers to what it was (or even goes higher!) once the extra power is routed to the HVAC.

 

[Ziv]

Interesting. It took 23 minutes to get up to 125 amps, or, probably more accurately, about 20 minutes if you subtract the time it was shut down. GM's engineers seem to have programmed the Bolt to really treat the pack gently.
And I think Q is right. If they install a higher amperage charger, say a 75 kW DCFC'er near you Bro, I would bet that the Bolt will charge at a faster rate than it has so far. So the Bolt is not limited by its own charging limitations right now, but by the limitations of the DCFC'ers that are available. That makes me think that the GM engineers have done a good job, again, by future proofing the Bolt so that it will be able to charge at state of the art chargers for the near future. And I think 75 kW DCFC chargers may be as good as it gets for 3 or 4 more years, if not longer.

Here's a chart of my charge session.

View attachment 130545

 

[bro1999]

Interesting. It took 23 minutes to get up to 125 amps, or, probably more accurately, about 20 minutes if you subtract the time it was shut down. GM's engineers seem to have programmed the Bolt to really treat the pack gently.
And I think Q is right. If they install a higher amperage charger, say a 75 kW DCFC'er near you Bro, I would bet that the Bolt will charge at a faster rate than it has so far. So the Bolt is not limited by its own charging limitations right now, but by the limitations of the DCFC'ers that are available. That makes me think that the GM engineers have done a good job, again, by future proofing the Bolt so that it will be able to charge at state of the art chargers for the near future. And I think 75 kW DCFC chargers may be as good as it gets for 3 or 4 more years, if not longer.

That's what I think too! And if it is true (Bolt can charge higher than 125A), a guy I know owes me $100.

I still think the slow ramp up had to due with the battery temp....it seems 70F may be the magic temperature where max charging is unleashed.

 

[Qinsp]

That's what I think too! And if it is true (Bolt can charge higher than 125A), a guy I know owes me $100.

I still think the slow ramp up had to due with the battery temp....it seems 70F may be the magic temperature where max charging is unleashed.

No basis for the following, but here goes:

The slow ramp could also be on the charger end. These were engineered for cars with ~20kWh batteries some air-cooled. They might have come up slow to make sure the car had plenty of time to respond to temperature climbing.

 

[hvacman]

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?

 

[jsmay311]

That's what I think too! And if it is true (Bolt can charge higher than 125A), a guy I know owes me $100.

I still think the slow ramp up had to due with the battery temp....it seems 70F may be the magic temperature where max charging is unleashed.

Even if the Bolt is capable of accepting 200A, the slow temperature-limited ramp-up, combined with the aggressive tapering over 50-55% SOC, suggests that that might not actually help speed things up that much.

Seems like a more powerful battery heater could've/should've been employed to accelerate the ramp-up. The amp limits in this instance aren't too bad (starting with a moderate-warm battery), but they're more severe when starting with a colder battery.

 

[jsmay311]

No basis for the following, but here goes:

The slow ramp could also be on the charger end. These were engineered for cars with ~20kWh batteries some air-cooled. They might have come up slow to make sure the car had plenty of time to respond to temperature climbing.

That's not how it works. The car tells the charger how much power it wants, and the charger delivers it (up to its maximum current rating).

Absent malfunction, there should be no self-limiting from the charger.

 

[phil0909]

Also, assuming the SOC-R values are accurate, I think we can conclude the bottom buffer of the Bolt's battery is 3-4%

Hello bro -

1. How did you arrive at this conclusion?
2. Does the SOC-R match what's reported in the Onstar app or myChevrolet? Or do the apps show SOC similar to what the station reports? Or perhaps a third SOC value?

Thanks for the info,

 

[Ziv]

I don't know jsmay. It took 20 minutes to get up to 125 amps and 40-42 kW charge rate, but if the increase in charge rate had continued up to 60-62 kW charge rate, the final 15 minutes would have delivered around 15 kWh instead of 10 kWh, plus an extra kWh or two during the 5 minutes between 40-42 kWh rate and when the charge rate tops out. So the 5 transitional minutes plus an extra 15 minutes at the higher rate would net you an additional 24-26 miles of highway speed range, which is nothing to sneeze at.
That presupposes that the Bolt will top out at a little over 80% of the nominal rating of the charger, or 40-42 for a 50 kW charger and 60-62 for a 75 kW charger.

Even if the Bolt is capable of accepting 200A, the slow temperature-limited ramp-up, combined with the aggressive tapering over 50-55% SOC, suggests that that might not actually help speed things up that much.

.

 

[Ladogaboy]

Even if the Bolt is capable of accepting 200A, the slow temperature-limited ramp-up, combined with the aggressive tapering over 50-55% SOC, suggests that that might not actually help speed things up that much.

Seems like a more powerful battery heater could've/should've been employed to accelerate the ramp-up. The amp limits in this instance aren't too bad (starting with a moderate-warm battery), but they're more severe when starting with a colder battery.

I still can't figure out why bro's Bolt EV ramps up so slowly. My Bolt EV immediately ramps up to the maximum amperage rating of the station. Now, it could be that bro's battery is conditioning, and if that is the case, what you are seeing is not a "ramping up" of current. You are seeing the battery's conditioning taking amperage away from the charge. I doubt that the Bolt EV will charge at 200 A (150 A is more likely), but I do believe the Bolt EV would take advantage of a 175-200 A station because it would redirect current beyond what the battery can accept to battery conditioning system.

By the way, Brian, what PIDs are you using to capture voltage and amperage? My Torque Pro doesn't seem to be picking up the DCFC charge rates.

 

[gpsman]

My car today.

Outdoor temp, about 60F.
Battery temp (no reading but must have been close or a little more).

Starting SOC 40%
Ending SOC 87%

60 minutes uniterrupted DCFC

 

[Ladogaboy]

My car today.

Outdoor temp, about 60F.
Battery temp (no reading but must have been close or a little more).

Starting SOC 40%
Ending SOC 87%

60 minutes uniterrupted DCFC

What station was that where you got one hour uninterrupted?

I just got ~ 40 kWh in 50 minutes starting at 8% SOC and ending at 64% SOC, but I had to restart after 30 minutes. That was on a 125 A charger.