Inaccurate meter

[leshore]

Curious...how accurate is the power consumption readout on the Trip Meter? How accurate is SCE's Meter? As illustrated below, since I took delivery of my Model S on April 19, the car has consumed 270.6 kWh. My ev-dedicated SCE meter shows that I have drawn 316 kWh. A difference of 45.4 kWh. Why such a difference? Where is the discrepancy? At first I thought last night's charge, which has not yet been used. However I drove fewer than 30 miles yesterday, and the 45.4 kWh translates to approx. 139 miles. SCE says to check next month's bill, and if it still is off substantially, they will check the meter. Has anyone else experienced this?

 

[snooper77]

Charging losses obviously, about 15%, that's to be expected.

 

[Cottonwood]

Curious...how accurate is the power consumption readout on the Trip Meter? How accurate is SCE's Meter? As illustrated below, since I took delivery of my Model S on April 19, the car has consumed 270.6 kWh. My ev-dedicated SCE meter shows that I have drawn 316 kWh. A difference of 45.4 kWh. Why such a difference? Where is the discrepancy? At first I thought last night's charge, which has not yet been used. However I drove fewer than 30 miles yesterday, and the 45.4 kWh translates to approx. 139 miles. SCE says to check next month's bill, and if it still is off substantially, they will check the meter. Has anyone else experienced this?

It's actually remarkably consistent. The power used, as reported in the car, only shows battery power used when the car is "On." The AC charger in the car is about 90% efficient; 270 kWh/90% is 300 kWh. The rest is power used when the car is off, "vampire load." This also includes turning on climate control with the App while the car is "Off." 16 kWh in 18 days to feed the vampire is very plausible.

Welcome to Tesla energy accounting...

 

[bonnie]

(mod note - fixed typo in thread name)

 

[leshore]

It's actually remarkably consistent. The power used, as reported in the car, only shows battery power used when the car is "On." The AC charger in the car is about 90% efficient; 270 kWh/90% is 300 kWh. The rest is power used when the car is off, "vampire load." This also includes turning on climate control with the App while the car is "Off." 16 kWh in 18 days to feed the vampire is very plausible.

Welcome to Tesla energy accounting...

That explains it. I didn't realize that the trip meter only displays energy used while the car is on. Thank you, Cottonwood.

- - - Updated - - -

(mod note - fixed typo in thread name)

Thank you, Bonnie, for fixing the typo.

 

[ThosEM]

It is pretty well documented that the rectifiers on board the Model S have about 85% efficiency, though I can't point to specifics off the top of my head. Your numbers are consistent with that. All the internal reporting is with respect to the actual power transferred from the battery.

 

[miimura]

That explains it. I didn't realize that the trip meter only displays energy used while the car is on. Thank you, Cottonwood.

In addition, the car is showing the energy taken out of the battery. Your electric meter shows the energy required to fill the battery. The two figures you showed are in exactly the expected ratio.