GMC HUMMER EV Forum | HummerChat.com banner
21 - 36 of 36 Posts

·
Registered
GMC Sierra, Bolt, Sky, Mach E
Joined
·
718 Posts
The heat in the cable and head are relative to the amps, not the kW going through them. TFL changed the EVGo screen a couple of times to show the volts/amps when it was at 300 kW and it showed only about 400 amps. We've seen EVGO chargers handle a full 500 amps for extended times with Rivians and other high-kWh 400 volt-based EVs. I think this is something within the EV throttling. As others noted, TFL left the EV "on" and the cabin cooling "on". If you are running the EV and have the HVAC in cooling mode and the EV thermal management prioritizes the cabin cooling, it will starve the glycol chiller and not provide full pack cooling capacity. I've seen Ioniq 5's get hit with both that situation when charging in other videos.
Others on the forum have seen the drop off without running the AC. I am not saying it is the charger, but simply not ignoring that.

The Hummer will be at the high currents longer than the other EVs due to the bigger battery. All the cars are less than half the battery of the Hummer and the Rivian is 60% of it. I have no idea what level of testing has been done on these chargers, in terms of output versus time. The chillers for the cable cooling have to work hard also, and those are fairly small.
 

·
Registered
GMC Sierra, Bolt, Sky, Mach E
Joined
·
718 Posts
I think I have found evidence that cell and pack voltage vs SOC while charging and after resting a bit may also be a factor about these variable and apparently unpredictable charging situations. I stumbled on a recent GM patent application for a charging control scheme that focuses on the cell voltages at various SOC's that can create dendrites. It creates multiple charging tables the BMS can use to regulate the charging amps, depending on the SOC at charge session start. Apparently, if you start from zero SOC at at a high charge rate, the cells hit that critical voltage earlier than if you start the charge session at higher SOC's. I have attached the charging curve chart included in the patent application that shows how the charge curves could vary depending on the SOC starting point. Note this is for a peak of 190-200 kW charging, which suggests the Lyriq pack was the example pack used.

I really need to dive into this further....it could be a gold mine of Ultium-based pack charging information. Stay tuned. View attachment 3125
My Mach E varies the curve based on starting SoC. With 50% or less, it will start at 150-160kw, then throttle back to 120 after a few minutes. But even when starting above 50%, it will start at higher kw than the curve when starting at low SoC. But it always limits to 45kw at 80%, no matter where it starts charging Or no matter the kw level at that point.
 

·
Registered
Volt, Polestar 2, R1T, Livewire One
Joined
·
946 Posts
Others on the forum have seen the drop off without running the AC. I am not saying it is the charger, but simply not ignoring that.

The Hummer will be at the high currents longer than the other EVs due to the bigger battery. All the cars are less than half the battery of the Hummer and the Rivian is 60% of it. I have no idea what level of testing has been done on these chargers, in terms of output versus time. The chillers for the cable cooling have to work hard also, and those are fairly small.
On a 95 degree day, I plugged into an EVGo station with my Rivian. It pulled 495A for ~5% increase in SoC before I got a message about the station throttling the charge rate. I didn't see what the station said current wise but the Rivian said it was taking in 59kW, so I'm guessing the station was throttled to 150A, which matches what they were seeing in the Hummer at that period of time, so it's a hell of a coincidence if it was the Hummer limiting the charge rate here.
 

·
Registered
GMC Sierra, Bolt, Sky, Mach E
Joined
·
718 Posts
On a 95 degree day, I plugged into an EVGo station with my Rivian. It pulled 495A for ~5% increase in SoC before I got a message about the station throttling the charge rate. I didn't see what the station said current wise but the Rivian said it was taking in 59kW, so I'm guessing the station was throttled to 150A, which matches what they were seeing in the Hummer at that period of time, so it's a hell of a coincidence if it was the Hummer limiting the charge rate here.
That is a clear indication the charger is not keeping the cable from over heating. The cable is a very small mass with that current going through it, but the battery is a much larger mass with that current distributed across many cells an modules. The battery will heat up much slower than the cable.

The other clue is that the rate drops fast and then actually ramps back up, the BMS would not normally react that fast because of the thermal time constant of the battery mass.
 

·
Registered
Volt, Polestar 2, R1T, Livewire One
Joined
·
946 Posts
Wow, 343 miles, hard to believe, way over predictions. I doubt that preconditioning the battery would even make that much difference, at least not in summer weather.
Sounds like he had optimal temps. No energy used for heating or cooling. The wind direction probably helped on the return trip significantly.
 

·
Registered
GMC Sierra, Bolt, Sky, Mach E
Joined
·
718 Posts
Tom M posted the charge curve on today's IEVs podcast. He had major problems that appeared to be vehicle-related. He has reached out to GM for a response.

Start around 1:10:00 on the video.

IEV Video podcast
I am going to speculate here, but it looks like this truck may be switching from 800V to 400V when this occurs. Could be some bad contactors in the switching circuits. It would be at about 400A in either case, if you look the power, it basically gets cut in half. If he was at an EVGO station, this could be confirmed.

This does not necessarily match what TFL or others on this forum have seen, although the dip is similar, this one is occurring much sooner in the charge.
 

·
Registered
Volt, Polestar 2, R1T, Livewire One
Joined
·
946 Posts
I am going to speculate here, but it looks like this truck may be switching from 800V to 400V when this occurs. Could be some bad contactors in the switching circuits. It would be at about 400A in either case, if you look the power, it basically gets cut in half. If he was at an EVGO station, this could be confirmed.

This does not necessarily match what TFL or others on this forum have seen, although the dip is similar, this one is occurring much sooner in the charge.
GDS2 shows what the voltage split is between the pack halves. It looks like the special charging circuit is capable of balancing the two halves of the packs without dropping out of the "800V" mode, but if it goes too far out of balance, who knows.
 

·
Registered
GMC Sierra, Bolt, Sky, Mach E
Joined
·
718 Posts
GDS2 shows what the voltage split is between the pack halves. It looks like the special charging circuit is capable of balancing the two halves of the packs without dropping out of the "800V" mode, but if it goes too far out of balance, who knows.
I looked back at the TFL video, and the station did indicate 766V after the dip, there was one point where he switched back to that display. But the power dropped all the way to 12kw at that switch point, which is really strange. That low of power seems to indicate it actually stopped the charge for a short period, then it started up again.
 

·
Registered
Volt, Polestar 2, R1T, Livewire One
Joined
·
946 Posts
I looked back at the TFL video, and the station did indicate 766V after the dip, there was one point where he switched back to that display. But the power dropped all the way to 12kw at that switch point, which is really strange. That low of power seems to indicate it actually stopped the charge for a short period, then it started up again.
It's probably pretty important to maintain balance between the split. I would have liked to spend more time datalogging and researching exactly how the process works but I sure as hell wouldn't be dropping the battery out and opening it up to investigate up close.
 

·
Registered
GMC Sierra, Bolt, Sky, Mach E
Joined
·
718 Posts
GDS2 shows what the voltage split is between the pack halves. It looks like the special charging circuit is capable of balancing the two halves of the packs without dropping out of the "800V" mode, but if it goes too far out of balance, who knows.
The pack gets split into two halves and then put in series, I do not think they are dynamically balancing them. When they switch back to parallel, there may be a small transfer of power from one "half" to the other to balance the overall voltage, but it should not be significant, and would have a resistor in between to balance them, then switch the regular contactors. They have to do this for the initial charging as well, it cannot be a hard switch, it is called a "pre-charge" circuit that is used even in charging of batteries that are just 400V without any switching.

I think GM has a software bug or software design issue causing this, maybe a sensor input issue/glitch. That steep dip in kw that the TFL guys saw sure indicates charging stopped for a moment. I am then guessing what Tom M saw was it completely stopped and did not turn back on, sicne he said he had to restart the charge.
 
21 - 36 of 36 Posts
Top