Miles per KwH - DC Fast Charging vs Charging at Home?

[StrikesTwice]

Which has nothing to do with OP's issue, this time of year, dropping from 2.2 (which is not achievable at 70mph) to 1.7 which is exactly correct.

Which has nothing to do with OP's issue, this time of year, dropping from 2.2 (which is not achievable at 70mph) to 1.7 which is exactly correct.

Cool dude, I’m glad you can speak with absolute certainty. I’m
Sure it’s whatever you said.

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[Enginerd Josh]

I've seen the same thing qualitatively with my 24 Flash. The specific difference between charging at home (I'm assuming at around 7kW) and charging at a DCFC (where I regularly see 150 kW) is charging speed. This can highlight a phenomenon called 'surface charge'. Here's what the internet says: " Surface charge is a temporary layer of voltage that sits on a battery’s plates immediately after charging, making the battery appear more fully charged than it actually is." This implies that using a DCFC and charging to say 80% indicated might not actually be giving you the same 80% that you'd get charging more slowly. Then the decreased indicated mi/kWh efficiency might just follow from that. I think we need to experiment: next time I get the chance, I'm going to use a DCFC near home, take my charge from 20% up to 80%, disconnect the charger, then sit and read a book for a few hours, checking charge every 20 minutes or so to see if surface charge dissipating significantly reduces my indicated charge level.

On the efficiency front in general: you can't overstate the effect of higher speeds on efficiency. At 60 mph on a flat road in 60F weather, I see 2.4 mi/kWh. At 70 mph, it's more like 1.9 mi/kWh. I run a cab-height canopy.

Ok, here some real world numbers with my 24 Flash 131kWh battery. I DCFC'd from 18% to 80%. Charge rate varied between 114kW and 139kW. Outside air was 60F. The Ford app billed me for 82.5 kWh, which is about 63% of 131 kWh. This seems reasonable for a very efficient DCFC in moderate temps and allowing for some wiggle room for onboard state of charge measurement.
I didn't drive very much over the next few days. Here's what I saw at T+x hours and n miles after charging:
@T+1 hour and 1.5 miles since charge: 80%
@T+2 hours: 80%
@T+12 hours: 80%
@T+13 hours: and 3.2 miles since charge: 80%
@T+23 hours and 12.6 miles since charge: 78%
@T+48 hours and 19.6 miles since charge: 76%
End test
HIghest temps seen 75F, lowest temp 36F
This driving was in-town, stop and go. I'm not a grandpa, but I drive like one.

Analysis: This data goes against my "DCFC causes surface charge which leads to overestimating battery state of charge until you unplug and hit the highway" idea. The charge applied at the DCFC didn't sneak away somehow. It stayed until I used it up by driving around. Because I was driving mostly at 35 and below, I saw pretty a pretty healthy miles per % charge. I expect that at highway speeds, my miles/%charge would've come way down. For now I'll stick with my mental model of "go faster, lose range; go uphill, lose range; drive against a strong headwind, lose range; put canoes on the roof, lose range but have fun".

 

[Tony Burgh]

It‘s common knowledge that DC electrons are sluggish and lazy.
Or maybe that’s DC politicians. I get confused a lot in my old age.

 

[PreservedSwine]

Took our second long trip in our Lightning, and noticed something really strange.

We charged to 100% at home before we left (70 degrees), and we averaged 70MPH, and 2.2 Mi/KwH on the GOM.

After the first charge, and from that point on, I couldn't get better that 1.7 Mi/Kwh, no matter how slow or fast I drove, with the same 70 degrees, and same accessories running.

I realize the GOM isn't entirely accurate, but we did see range calculations slip also, and am curious if there is a technical reason why this would happen?

Extrapolate your battery percentage, to kilowatt hours on the battery, from there you can math out your actual kilowatt hours per mile.

EDIT:

Wanted to add, on my real world experience.

Just like fuel gauges are not accurate, I'm not entirely sure the battery percentage indicator is either.
When I charge a 100%, I get pretty ridiculous miles per kilowatt numbers for the start of any trip, and my battery percentage declines at a lower rate than if I start the same trip @ 50%.
In hindsight, I naively assumed all lightning showed the same behavior. In retrospect I have no clue how other lightings behave.

 

[hturnerfamily]

in over 68,000 miles over 3 1/2 years, and many of that towing a camper or trailer, I've never seen any difference between 'where' I charge, or 'how' I charge... whether DCFC, or at home, 240v 30amp at 7.2kwh, or 120v at 1.2kwh... the 'speed' is the only difference, in the end.

 

[Shmoe]

Residential vs commercial electrons

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