Model 3 Charging Efficiency

[AlanSubie4Life]

The odometer reading in your Tesla reports 'Drive kWh' none of the other stuff is counted like radio, lights, heater, AC etc.

That is incorrect. All energy is counted as long as you are not in Park (very important!).

You don’t have to believe me, it is easy to verify.

 

[rejedejo]

Well, since we're kicking an old thread here...





I know both of you may not be on the forum anymore, but what both of you are seeing is probably not mostly explained by charging efficiency. It's more probably the "1% loss per day" that Tesla claims. According to the Stats app for iOS, this is actually about 1.33kWh/day (median from their fleet), which is roughly 1.8% on an LR pack and 2.6% on the SR+ pack. It's almost equivalent to a 60W incandescent bulb constantly burning, powered by your car. This is nearly 500kWh/year, or the equivalent of putting on about 2000 miles.

For @Dbregmam specifically, you have a 80kWh discrepancy over just two months so far. Extrapolated to a year that would be 480kWh, which is indeed nearly 500kWh/year that would be the median standby usage for Model 3.

Yep, the odometer only reports 'drive' kWh all the other stuff doesn't count toward that number. I use about 420 Watt hours / mile, long term average.

 

[rejedejo]

That is incorrect. All energy is counted as long as you are not in Park (very important!).

You don’t have to believe me, it is easy to verify.

How?

 

[AlanSubie4Life]

How?

Do an experiment with heat on max (you can and should leave windows open to prevent transient effects - need open loop operation). Drive a fixed course of 1-2 miles round trip. Log the data. Exit the vehicle.

Do the same course with HVAC turned off. Log the data. Exit the vehicle.

You can figure out how to devise an experiment for the park/no park scenario (it’s not too hard - just have a control scenario, and compare to that). For example you could stop halfway through your 2-mile course with heat on high and spend a significant fraction of time in park there. Then carry on and see how it compares. Can do the same stop for the same time, not putting the vehicle in park.

 

[AlanSubie4Life]

Tesla won't do this without being required because their numbers wouldn't look nearly as good.

It’s certainly true that the various sources of vampire and feature drain are not properly accounted for in the EPA test. That being said, it does seem that there have been improvements in the sleep behavior of Teslas and that has driven down those losses to perhaps 300kWh per year not including feature drain.

However, any use in the EPA test with the vehicle in park IS measured (even if it does not show on the meter). They charge up the vehicle the night before or something as I recall (don’t know the exact rules). In any case these losses would be small given the duration of the test, and are not representative of what those losses would typically be (since vehicles spend most of their time parked, unlike in the EPA test).

 

[miimura]

There was an EPA test that was repeated because there was abnormal drain overnight between charging and running the test. I believe there was some statement from Tesla about the logs that said the door wasn't properly closed or something while parked. EPA denied it, but ended up redoing the test and Tesla's position was validated. At least that's the way I remember it.

 

[AlanSubie4Life]

There was an EPA test that was repeated because there was abnormal drain overnight between charging and running the test. I believe there was some statement from Tesla about the logs that said the door wasn't properly closed or something while parked. EPA denied it, but ended up redoing the test and Tesla's position was validated. At least that's the way I remember it.

Yep. That’s how I remember the story too. Anyway, the point remains: some of the drain is counted in the test, it’s just not representative of normal use, due to the proportion of time spent in idle/sleep vs. driving, for the window of time used for the EPA test.

 

[AlanSubie4Life]

I use about 420 Watt hours / mile, long term average.

I assume this is your wall-to-wheels number counting everything. I’d guess with that value, your in-car trip meter over the period of ownership is reading about 280Wh/mi-300Wh/mi. Rule of thumb for a colder area like Ohio is something like 1.4 or 1.5 I think. Could be higher if you drive less, which many are these days.

The EPA factor used is around 1.14 (88% charging efficiency).

 

[rejedejo]

Do an experiment with heat on max (you can and should leave windows open to prevent transient effects - need open loop operation). Drive a fixed course of 1-2 miles round trip. Log the data. Exit the vehicle.

Do the same course with HVAC turned off. Log the data. Exit the vehicle.

You can figure out how to devise an experiment for the park/no park scenario (it’s not too hard - just have a control scenario, and compare to that). For example you could stop halfway through your 2-mile course with heat on high and spend a significant fraction of time in park there. Then carry on and see how it compares. Can do the same stop for the same time, not putting the vehicle in park.

Log the data. Exit the vehicle.

Where are you getting data?

 

[rejedejo]

I assume this is your wall-to-wheels number counting everything. I’d guess with that value, your in-car trip meter over the period of ownership is reading about 280Wh/mi-300Wh/mi. Rule of thumb for a colder area like Ohio is something like 1.4 or 1.5 I think. Could be higher if you drive less, which many are these days.

The EPA factor used is around 1.14 (88% charging efficiency).

Exactly! Wall-to-wheels. Thank you for that simple way of saying what I mean. I think that main "Wall" number should be published, right below your odometer. Seems like a reasonable requirement. And, you can pay your friend right when you charge at their house. Gasoline pumps log to .001 gallons, so you know exactly how much energy goes in. My car knows it exactly too, just won't tell me.

 

[AlanSubie4Life]

Where are you getting data?

The trip meter. Read it right after you put the car in park, for each experiment (this forces it to update).

 

[AlanSubie4Life]

My car knows it exactly too, just won't tell me.

That’s correct, it does, to a high degree of accuracy. I agree it would be nice if Tesla just tracked this data, and broke it out for you. It seems silly that the car doesn’t tell you how much feature and vampire drain you have (and unlike the third-party apps, they could discriminate between BMS re-estimation and actual rated mile energy use - sometimes miles go up by 2-10 miles when you are just sitting, and Tesla could keep track of all this sort of shift separately), and what your charging losses are.

If this were presented, people could actually make smart decisions on whether to upgrade their charging setup, etc.

As it is, people rely on third-party apps to approximate the numbers, instead.

Wall-to-wheels. Thank you for that simple way of saying what I mean

Again, for the record, the EPA numbers are wall-to-wheels efficiency. However, they miss various usage as mentioned above.

 

[rexki]

The API are supplying this data to my understanding, so I get the charge efficiency data on my teslafi.com page for my S.

View attachment 293390

You can get the two first week for free or you are welcome to use my referral code for a free month, which is Veritas (case sensitive).

72 amps !! - where does this person live?

 

[rrolsbe]

That’s correct, it does, to a high degree of accuracy. I agree it would be nice if Tesla just tracked this data, and broke it out for you. It seems silly that the car doesn’t tell you how much feature and vampire drain you have (and unlike the third-party apps, they could discriminate between BMS re-estimation and actual rated mile energy use - sometimes miles go up by 2-10 miles when you are just sitting, and Tesla could keep track of all this sort of shift separately), and what your charging losses are.

If this were presented, people could actually make smart decisions on whether to upgrade their charging setup, etc.

As it is, people rely on third-party apps to approximate the numbers, instead.

Again, for the record, the EPA numbers are wall-to-wheels efficiency. However, they miss various usage as mentioned above.

I think the internet connected Gen 3 Tesla Wall Connector could get VERY close to the actual amount of energy used by the vehicle. Since the car and the Wall Connector are connected to the local Wifi they should be able communicate with each other. I think they might also be able to communicate over the charging cable? The Wall Connector knows what the open circuit voltage is before charging begins so it can measure what you are actually paying for fairly accurately during a charging session. Open circuit voltage X charging current X time = "KWH you are paying for" (not what the car reports or the power delivered to the cars charge port connector), this would even take into account the energy lost heating the house wiring (ie. voltage drop) and the charging inefficiencies/overhead. The Wall Connector should be able to read the odometer in the car along with the "KWH you are paying for" to determine the actual Watt hours per mile used. A fairly detailed monthly report could be generated that could help the owner understand the actual charging costs. If the Gen 3 Wall Connector had these features, that would be a very BIG value added proposition. As it stands now the Gen 3 Wall Connector has very few features.

 

[SageBrush]

A fairly detailed monthly report could be generated that could help the owner understand the actual charging costs. If the Gen 3 Wall Connector had these features, that would be a very BIG value added proposition. As it stands now the Gen 3 Wall Connector has very few features.

If this is important to you, it is trivial to slap on a wi-fi enabled CT inside your panel. They are cheap these days. What you are calling BIG is a $20 add-on.