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

[telrod11]

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?

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[hturnerfamily]

the GOM is only using 'recent' driving data when you begin a day, a trip, etc., and has no way of knowing where you are going, how fast you'll be driving, or the conditions during the trip.

the second leg of your trip, it now knows a different story - 70 mph, etc.

there is no difference in 'slow charging' at home, and 'fast charging' on the road - power is power, and neither has any difference in 'effect' on the GOM...

the GOM is exactly that - a guesstimation. The real numbers are your Miles Traveled divided by KWH used.

I've noticed on mine whether I've had a good KWH usage day, or not, the GOM still uses a base 2.1mi/KWH for the balance of the 'Range Estimate' it provides.

 

[hturnerfamily]

1.7mi/KWH sounds about 'right' if traveling 70mph

2.2mi/KWH would be VERY GOOD, down hill, at 50mph... and after the past many miles were 'around town' at 40mph average...

 

[RickLightning]

This Trip is where your miles per kWh is displayed before you power off. GOM doesn't display it... It is accurate.

 

[StrikesTwice]

My efficiency takes a bit of a hit after DC fast charging as well. Once I finish a session, I notice my battery is a bit warmer. I believe I’m losing efficiency because the truck is using more energy to cool the battery.

 

[Firn]

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?

The GOM is the miles to empty, not the efficiency. I don't think many have reported seeing inaccuracy in the mi/kwh although yours is a pretty extreme difference.

We really don't know well at all how the gom and the efficiency works. We know there must be some historical weighting to it, likely just the last few minutes, but we cannot be sure.

I will say that 2.2 is very high for 70mph, and 1.7 is low. I would be more likely to believe the 1.7 than the 2.2.

No good answer for you other than potentially the "extra" charge going to 100% gives (not really extra, just bms calibration), or maybe there was more surface roads at the beginning of the trip. That's my thoughts

 

[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.

 

[RickLightning]

My efficiency takes a bit of a hit after DC fast charging as well. Once I finish a session, I notice my battery is a bit warmer. I believe I’m losing efficiency because the truck is using more energy to cool the battery.

After fast charging, the battery is mid 90s or higher. And no, you're not losing efficiency from cooling to the extent that is mentioned in the original post.

 

[K6CCC]

On my 1000+ mile trip a few weeks ago, I also noticed my miles / KWH was lower that normal, but it was entirely due to very high heat and high speed. For a good part of the trip, the speed limit was 75, so lots of driving at close to 80. Because it was so hot, if I got out of the truck for almost any stop except overnight, I left the truck On to keep the AC running.

https://www.f150lightningforum.com/...rt-glendora-ca-to-tucson-az-and-return.35747/

 

[hajalie24]

Something interesting I notice sometimes when charging to 100% is sometimes it legit seems like the truck decided to use the extra 7kwh of reserve battery. It then takes like 15 miles of driving before the battery percentage goes to 99%, and I believe the efficiency shows a higher than usual number too.

 

[chl]

I'd suspect two things:

1) a re-calibration of the guessing by the truck compooter based on (a) your first leg driving, and
(b) based on the fact that the truck used energy during the fast charging for thermal management so that extra energy usage is factored into the calculation;

2) a rise in battery temperature lingering after a fast charge, compared to the first leg.

Another factor could be the preconditioning of the battery as you approach the next DCFC station, if that was going on for your next leg of the journey?

This seems to be something that has been reported before by F-150 Lightning owners after charging, e.g,

https://www.f150lightningforum.com/forum/threads/bad-mi-kwh-after-charging.21004/

 

[StrikesTwice]

After fast charging, the battery is mid 90s or higher. And no, you're not losing efficiency from cooling to the extent that is mentioned in the original post.

I would disagree. The ambient temperatures are already in the mid 90’s on the Florida turnpike in the summer. After a charging session, I can see the increased temperature on my gauge. And my efficiency is down until that battery cools off to its normal temperature.

 

[RickLightning]

I would disagree. The ambient temperatures are already in the mid 90’s on the Florida turnpike in the summer. After a charging session, I can see the increased temperature on my gauge. And my efficiency is down until that battery cools off to its normal temperature.

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.

 

[Zprime29]

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.

Disagree about the achievable numbers. I've hit 2.2 several times on my trips between Tucson and El Paso in those temps @ 70mph. It's largely dependent on winds. I've never gotten as low as 1.7 @ 70mph unless on a steep incline. Even with a 10-15mph head wind I usually see 1.8-1.9. (Trailing a semi that's cruising at 70mph helps too)

2.1 is what @tommolog got on his 70mph test and even the Consumer Reports article reported 270 miles of range which is 2.06. So 2.2 with a slight tail wind or decrease in elevation is very much achievable. My commute from home to work only drops 500ft and yet I get 3.1 vs 2.4 going home, so it doesn't take much change to make an impact.

My best guess is that the wind picked up/changed direction after the OP's charging stop and possibly started driving uphill more. I've never charged to 100% on a DCFC, so I don't have any first hand experience that's directly comparable. Most I think I've waited on is to 90%.

 

[telrod11]

Thanks for all the replies guys.

I'm on a short trip right now after charging to 70% last night (home charging)

I've attached a photo of 65mph and the 2.2 that I get regularly.

I'm really not sure why that last trip lost .5 after DC fast charging.

Not trying to cause any arguments here, just truly curious.

Thanks

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