Data from "State of Charge" and "Out of Spec" channels

[Smorgasbord]

State of Charge has a new video out on their perspective of the Eastern Edge race. I grabbed this screenshot from a 400kW EA charger:

He did it cumulatively, but I was more interested in incremental, so:

Starting SOC (approx.)	Time to add 50 EPA Miles	Avg Time Per Mile
0%	168 seconds	3.36 seconds/mile
11.1%	144 seconds	2.88 seconds/mile
22.2%	150 seconds	3.0 seconds/mile
33.3%	174 seconds	3.48 seconds/mile
44.4%	222 seconds	4.44 seconds/mile
55.6%	282 seconds	5.64 seconds/mile
66.7%	342 seconds	6.84 seconds/mile
77.8%	540 seconds	10.8 seconds/mile

I was interested in finding the optimum point to stop charging and go to the next charger. Obviously, while the charging rate slows down (as much as a factor of 3.75!), the time from off-ramp to on-ramp also matters (time to get to charger, park, get out of car, plug, get the handshake going until actual start, then the small ramp-up time as the charger modules kick-on), then un-plug, get back in car, and drive to the on-ramp (including traffic lights both ways).

Let's say the ideal starting charge is below 10%, but above 0% (you can go lower due to the buffer), and choose a 2.9 seconds/mile number. At 56% (Tom's ideal stopping charge), you need 5.64 seconds to get a mile. That's 2.74 additional seconds/mile to keep charging instead. If we want to go from 11 stops on the Eastern Edge Race to 10 stops, well, let's look at the data:

First charge doesn't count for on-road charging, so they added 624.8 kWh on each of 11 stops. If we wanted to do 10 stops instead, that would mean adding, on average, 62.4kWh per stop instead of the about 57kWh per stop they actually did. That's a difference of about 5.4 kWh additional. At 2.7 miles/kWh, that's 14.6 additional miles needed.

Tom shows a chart and decided that 57% SOC was the ideal stopping point - and they came close to averaging that. At 57% SOC, staying on for 5.4kWh would add (14.6miles*5.64seconds/mile) 82.3 seconds per stop. Times 10 stops and that's 13.725 minutes. So, if they could do their stops with an average down time of less than 13.725 minutes, then Tom was right.

But, especially since his team was restricted to 225kW chargers (Tesla SCs), maybe the stopping SOC was even earlier. Look at how well Model X did with lots and lots of stops. It would be interesting to run this calculation the other way and see if SC Gravity maybe should have done even more stops to save some time.

 

[Smorgasbord]

I missed the 10minute edit window, and there's at least one mistake in my math. The delta time isn't just the 5.63 seconds/mile at 57%, it's the delta time at 57% minus the time at a under 10% SOC. So the above should be:

Tom shows a chart and decided that 57% SOC was the ideal stopping point - and they came close to averaging that. At 57% SOC, staying on for 5.4kWh would add (14.6miles*(5.64seconds/mile-2.9seconds/mile)) = 40 seconds per stop. Times 10 stops and that's 6.7 additional minutes. So, if they could do their stops with an average down time of less than 6.7 minutes, then Tom was right.

That makes it closer, but again this is with 400kW chargers, not the Tesla chargers his team was restricted to.

 

[XTesla]

I was thinking about it a different way...
I looked at Google Maps for some of the stops and it was a 5-7 minute detour (not counting handshake time, payment time, or rampup time etc)
Once I added in 7 minutes to the charging stops they had the average charging speed for the stop dropped down to 140kW or so.
Looking at a different chart he showed, they were stopping charge well above that rate... so my conclusion was that if they were able to keep charging and skip a charging station then it would be worthwhile if they can keep the charging speed above 140kW.
I haven't looked at the exact instances of where the charging stations were located, but if they were able to get a bit extra (and go a bit deeper into the reserve) then I expect taking fewer stops would be better (for the supercharger restricted car).

The X was in quite a different situation... it was driving 10% more efficient, so naturally could spend 10% less time charging (when both cars are locked to the same kW) but with range/charging curve had the downside of needing to make more stops to keep up the charging rate.

The other Gravity (not needing to use superchargers) needs further study as to why it didn't do much better. In theory it should have saved 5 minutes per charging session (when it can get a fast charge) and had the choice of more charging stations closer to the route. We know there were charging issues, which then leads to the question of whether picking slower superchargers is ultimately the better roadtripping experience simply due to higher reliability of charging, or if other factors were involved.

 

[Smorgasbord]

For the Model X, what do you think the average driving overhead time per stop was? With so many stops, they had to have been choosing only very close stops. I remember one moment where the Model X team was complaining about 3 traffic lights to get to a stop and that they had to find future stops with 1 or 0 traffic lights.

I don't think it's fair/accurate to say that the any-charger team had a choice of "more charging stations closer to the route," since it was looking for the higher than 250kW power stations, which I suspect are fewer than the 250kW Tesla stations along that route. The 150kW EA stations, for instance, were probably way more plentiful than the EA 350 stations, but the Mercedes and Ionna 400kW stations are probably way way fewer.

At losing by only 21 minutes for the Tesla chargers over 11 stops, that's just under 2 minutes per stop. We know some of why that was due to the any-charger Gravity having charging issues later in the race, apparently due to some combination of vehicle BMS issues (no AC charging nor idel time for the BMS to recalibrate), and overheating at high charge rates due to rising temps, but we'd need the kind of data Tom collected for Kyle's team to really compare, which we don't (yet) have.

It is interesting to see that even at the start of the race we knew that the results would not necessarily translate to real-world family vacation style road trips. That's because Kyle had spoken to Lucid engineers and found out that their design, as I just stated, was that the BMS recalibrates during either AC charging or just sitting idle. Since neither of those was possible once the race started, the side effects of that means a different result than for a typical multi-day 2100 mile trip (say 3 days minimum with 2 overnight idles and probably at least 1 AC overnight charge stop). We saw bugs requiring a car reset in both the Gravitys, the Model X, and the ID Buzz at least (I don't recall if the other vehicles had similar issues or not). And at this point, we can only speculate whether those were all/mostly/partially caused by the stress of back to back to back fast charging with no down-time, or just bugs in general that would have appeared in a multi-day equivalent trip.

My original point in posting was to move beyond Tom's assertion that 57% (or thereabouts) was the right point at which to stop charging. IIRC, he based that on this chart:

Where his vehicle was restricted to the black line, in which charging ramps quickly to 225kW (0-2%SOC), and then stays there until 45% SOC, and even at 57% SOC is still pulling 200kW, but then starts slowing down more rapidly. My goal was to figure out if they had held out until 75% SOC, which is another inflection point of charge rate (but still pulling 150kW) is that additional 23% of additional SOC (27kWh?) per charge would have resulted in them being able to remove a stop or two, and then whether that slowing of 50kW for that last bit was worse or better than the per stop downtime.

From what he says, I think Tom chose based on the graph's inflection points, and not on the actual time difference calculations, but I could be wrong. I do think the real math is more complicated, but worthwhile for the goals of this race.