Help me understand battery consumption

[AlanSubie4Life]

And to correct my post rated range is (approximately!):

75kWh/242Wh/mi * battery % = x miles.

The formula I gave was for 100% capacity.

Anyway I think the OP must have lost some range when sitting and not driving. It's conceivable that it could have been entirely vampire drain if the car was looking for an update. My car "drove" for at least 20 miles just sitting in the garage this weekend (partly because I was harassing it, and partly because it woke up early on Sunday morning to do some navel contemplation and consult with the Tesla psychologist in the cloud (based on WiFi traffic)).

 

[zanary]

For Model S and Model X, the usable capacity of the battery pack is never the actual size of the battery pack. I think WK056 discovered this and published his findings here. It's just a guess, but the same might be true with the Model 3.

Source = Tesla, please stop making up specifications... | wk057's SkieNET...
Source = Pics and Info: Inside the Tesla 100kWh Battery Pack | wk057's SkieNET

 

[jjrandorin]

@AlanSubie4Life

I know you have been tracking down vampire drain (from reading various threads here). Just as a data point for you in your quest to continue to track it down, in my specific case, I am losing about 1-2 miles a day, parked in my finished garage in Temecula.

Average temps in my garage is likely high40s overnight to low 60s during the day right now. I specifically do not have any monitoring apps installed other than the Tesla one. I originally (first couple days) installed status for tesla, and noticed I went from 1-2 miles per day 1 mile every 3-4 hours or so, and decided I didnt need the data that bad.

I only had the app installed for about 24 hours. Since uninstalling the app and changing my password on my tesla account to invalidate the token, I am back to 1-2 miles per 24 hours.

Since this thread is about mileage and drain, hopefully this is not too much off topic

 

[jjrandorin]

For Model S and Model X, the usable capacity of the battery pack is never the actual size of the battery pack. I think WK056 discovered this and published his findings here. It's just a guess, but the same might be true with the Model 3.

Source = Tesla, please stop making up specifications... | wk057's SkieNET...
Source = Pics and Info: Inside the Tesla 100kWh Battery Pack | wk057's SkieNET

I think this is one reason tesla did not want to name the model 3s like they did the S and X. We dont have a "Model 3 60d" or a Model 3 P75D+".

They just state miles, not battery pack capacity and I wondered why. This explains perfectly why, so thanks for posting it.

 

[AlanSubie4Life]

On Friday I left work with battery showing 278 miles @ 90%. 90% of 75kWh is 67.5 kWh. I drove around quite a bit all weekend and arrived at work today Monday with battery showing 30 miles left. My trip meter shows that I have driven 201.3 miles @ 248 Wh/mi 50kWh total since last charge.

@Redrick00
(278mi-30mi)/(310mi) * 75kWh = 60kWh

And you used 50kWh according to trip meter.

So yes you're missing 10kWh (about - it depends on the correctness of the 310mi and 75kWh constants above (equivalent to 242Wh/mi) - but they would have to be off by a LOT - and they're not).

I don't do long trips so I can't accurately check the constant, but the idea for the "experiment" would be:

Charge to a %, as high as possible, 90% is fine, check your miles.
Immediately drive for a long time to relatively low %, being careful to not do any sitting in park. Make sure trip meter is properly reset (should be).
Immediately check your miles. Immediately record all your trip meter info.
Fit data into the formulas above. The higher the number of miles driven the better the accuracy.

This experiment really just obtains the "true" Wh/mi constant and doesn't directly tell you the true full battery capacity. But you actually don't care about the true battery capacity - you were concerned about the discrepancy between the stated usage on the "since last charge" meter (50kWh), and the energy actually taken out of the pack (appeared to be close to 60kWh).
("Rated Wh/mi" = kWh on trip / (Initial miles - Final miles) )

Like I said I can't easily do this, so I assume this would end up with a number pretty close to 242Wh/mi, but I don't know.

 

[Redrick00]

Just want to say...this is not true. The rated range has nothing to do with "stuff". It is the capacity of the battery (whatever it decides that is, but for a "new" battery it appears to be about 75kWh (there is debate on this number, but it's close to this) divided by a constant which is about 242Wh/mi (so 75kWh/242Wh/mi = 310miles). These are somewhat approximate numbers, but the point is that the rated range is not given by an algorithm (with respect to driving style) and does not change unless battery capacity is determined to be lower or higher for some reason (VERY cold temperatures, age, etc. yes that's an algorithm but a little different than what was implied).


I think he meant in park, before you start driving, when he said "idling". The key point is that that "since last charge" data does not include losses when you're not in the car (which to some extent you already knew - but it's more than just the vampire/phantom losses, depending on exactly how you used the car). It probably doesn't include losses when you get into the car, before you put it in drive, either. When it "stops" and "starts" counting EXACTLY, I don't know. Anyway I think that's likely the reason for your 10kWh discrepancy, can you think of situations where you might have been sitting in park for any period of time? It's definitely high for 3 days of vampire drain but that could also happen under certain scenarios where the car decides not to sleep.

Ok, it’s possible that my wife might of sat idling somewhere as she drives my car any chance she gets. The trip meter for “since last charge” would be more helpful if it accounted for all power consumption not just while driving. Something like electrical meters do when you add CT transformers on conductors to record power consumption.

 

[Redrick00]

@Redrick00
(278mi-30mi)/(310mi) * 75kWh = 60kWh

And you used 50kWh according to trip meter.

So yes you're missing 10kWh (about - it depends on the correctness of the 310mi and 75kWh constants above (equivalent to 242Wh/mi) - but they would have to be off by a LOT - and they're not).

I don't do long trips so I can't accurately check the constant, but the idea for the "experiment" would be:

Charge to a %, as high as possible, 90% is fine, check your miles.
Immediately drive for a long time to relatively low %, being careful to not do any sitting in park. Make sure trip meter is properly reset (should be).
Immediately check your miles. Immediately record all your trip meter info.
Fit data into the formulas above. The higher the number of miles driven the better the accuracy.

This experiment really just obtains the "true" Wh/mi constant and doesn't directly tell you the true full battery capacity. But you actually don't care about the true battery capacity - you were concerned about the discrepancy between the stated usage on the "since last charge" meter (50kWh), and the energy actually taken out of the pack (appeared to be close to 60kWh).
("Rated Wh/mi" = kWh on trip / (Initial miles - Final miles) )

Like I said I can't easily do this, so I assume this would end up with a number pretty close to 242Wh/mi, but I don't know.

Thanks for reply, you really understood my question. My question was not a complain as to where are the missing kWh or why I’m getting less than rated miles, it is more of trying to understand how the car works. I enjoy this car and don’t baby it at all as I come from driving a Chrysler 300c with 340hp and I wanted something comparable in power and acceleration. I will try your recommendation on my next long trip, most of my driving composes of short drives around Southern California.

 

[docdeb27]

Ok. Please help explain thia to me. I charged to 99% last night appx 304 miles and drove appx 150 miles. When I got home it said I used over 200. Do I drive that fast (LIE 70s at times)?. 30 degrees outside, used seat warmer on low, heat 68, radio.

 

[animorph]

This is my best explanation of why the kWh measurements never match up (taking into account all the other things mentioned so far):

Car’s energy consumption (lack of) accuracy

So yes, the battery may have been charged with 75 kWh (by the way, the charging kWh added may be more accurate towards the 75 kWh total than the consumption numbers.) If you drive continuously and carefully at 25 MPH you might be able to pull out 75 kWh from the battery. If you accelerate harder and drive 70 MPH you will get less than 75 kWh out of the battery. That's just because you're using more current and seeing higher losses in the battery, which the trip meter kWh values don't see.

 

[AlanSubie4Life]

Ok. Please help explain thia to me. I charged to 99% last night appx 304 miles and drove appx 150 miles. When I got home it said I used over 200. Do I drive that fast (LIE 70s at times)?. 30 degrees outside, used seat warmer on low, heat 68, radio.

200 what? It said your efficiency was 200+ Wh/mi? Or your remaining range was ~100 miles (used over 200 miles)? The efficiency it gives you (your actual efficiency) is different than the rated efficiency. However, there is a direct relationship between the Wh used "since last charge" and the miles that are removed from your rated miles - with the exception of idle losses & vampire losses as mentioned above.

150 miles for 200 miles of rated range seems reasonable at 68 degrees with outside temp at 30. The heater was probably using at least 3kW over the ~3+ hours of driving - which would be 9kWh which would be at least 9kWh/242Wh/mi = 37 miles of rated range use only for heating the cabin.

EDIT: fixed my typo...

 

[docdeb27]

200 what? It said your efficiency was 200+ Wh/mi? Or your remaining range was ~100 miles (used over 200 miles)? The efficiency it gives you (your actual efficiency) is different than the rated efficiency. However, there is a direct relationship between the Wh used "since last charge" and the miles that are removed from your rated miles - with the exception of idle losses & vampire losses as mentioned above.

150 miles for 200 miles of rated range seems reasonable at 68 degrees with outside temp at 30. The heater was probably using at least 3kW over the ~3+ hours of driving - which would be 9kWh which would be at least 9kWh/242Wh/mi = 37 miles of rated range use only for heating the cabin.

EDIT: fixed my typo...

It said I used over 200 miles worth of elec range. I drove 150 miles. That's a big difference no?

 

[AlanSubie4Life]

It said I used over 200 miles worth of elec range. I drove 150 miles. That's a big difference no?

No, it seems about right. Look at the approximate calculation of heater consumption. That's what is getting you. That number is actually pretty easy to measure yourself if you have a 48A charger at home and can park the car outside in the ambient. Just crack a door slightly, plug in the car, set charging limit to lower than current battery %, crank up the heat on the app, and see what's on the screen from outside the car. Volts * Amps = Watts. It'll go as high as 10kW, or more. Then it will settle down to a few kW as the cabin comes to temperature - but you'll also be able to see the steady state. The on-board charger isn't 100% efficient so the actual heater use is a little lower than this; the charger waste heat presumably goes outside the cabin, though knowing Tesla maybe they scavenge it...but it gives an idea.

 

[docdeb27]

No, it seems about right. Look at the approximate calculation of heater consumption. That's what is getting you. That number is actually pretty easy to measure yourself if you have a 48A charger at home and can park the car outside in the ambient. Just crack a door slightly, plug in the car, set charging limit to lower than current battery %, crank up the heat on the app, and see what's on the screen from outside the car. Volts * Amps = Watts. It'll go as high as 10kW, or more. Then it will settle down to a few kW as the cabin comes to temperature - but you'll also be able to see the steady state. The on-board charger isn't 100% efficient so the actual heater use is a little lower than this, but it gives an idea.

Ok. So I need to plan on getting much less than 310 miles using either AC or heat. I'm happy As long as nothing is wrong with the car or my driving.

 

[AlanSubie4Life]

Ok. So I need to plan on getting much less than 310 miles using either AC or heat. As long as nothing is wrong.

Yeah, AC isn't nearly as bad though, since it's a reverse heat pump and is inherently more efficient (about 2-3 times better) than what is essentially resistive heating. You can check that using the method above when the summer comes. The exact numbers depend on the temperatures of course.

 

[docdeb27]

Yeah, AC isn't nearly as bad though, since it's a reverse heat pump and is inherently more efficient (about 2-3 times better) than what is essentially resistive heating. You can check that using the method above when the summer comes. The exact numbers depend on the temperatures of course.

Thanks. This is my first total EV and I do have a lead foot with this car. It's fun.

 

[RuiP]

This is my best explanation of why the kWh measurements never match up (taking into account all the other things mentioned so far):

Car’s energy consumption (lack of) accuracy

So yes, the battery may have been charged with 75 kWh (by the way, the charging kWh added may be more accurate towards the 75 kWh total than the consumption numbers.) If you drive continuously and carefully at 25 MPH you might be able to pull out 75 kWh from the battery. If you accelerate harder and drive 70 MPH you will get less than 75 kWh out of the battery. That's just because you're using more current and seeing higher losses in the battery, which the trip meter kWh values don't see.

Redrick00, this - and the linked thread - is the correct answer to your (correct) findings.

Summing it up: because of discharge losses (not accounted for in Tesla's energy consumption meter) you'll never, ever, ever be able to see the car report a +70kWh "energy consumption since last charge", even though the battery pack is ~75kWh.

 

[AlanSubie4Life]

Redrick00, this - and the linked thread - is the correct answer to your (correct) findings.

Summing it up: because of discharge losses (not accounted for in Tesla's energy consumption meter) you'll never, ever, ever be able to see the car report a +70kWh "energy consumption since last charge", even though the battery pack is ~75kWh.

Interesting. Like I said, I haven't had a chance to tabulate over a long haul. Do you know what the actual difference (difference: I guess extrapolated difference for a full discharge vs. 75kWh (which is allegedly the approximate capacity)) is for a long drive (as described in the experiment above)? I'm actually a little surprised that it would be off by very much for modest driving. Of course, the amount of energy you put into a battery when charging is going to be higher than what you get out of it, as it is not perfectly efficient (see the comments in the other thread) - but that's not the issue here. There are definitely a lot of factors to consider here! I still find it kind of doubtful that it would be off by as much as 10kWh...but wouldn't be surprised by 1-2kWh discrepancy, after eliminating vampire losses.

 

[Polly Wog]

I don’t agree on your second point because yesterday after charging I drove for 19 miles for a total time of 45 minutes. There was a lot of time stopped idling at red lights. My trip meter since last charge showed 19 miles 4kWh @ 209 Wh/mi. My trip meter since time I started driving also shows 19miles 45 minutes at the same 209 Wh/mi which tells me the calculation included the time spent idling.

View attachment 361930

Sorry, but I should clearly have said "idling while not in Drive/Reverse". Idling in the sense I was referring to is not the same as idling in a ICE, but time the car is sitting, while not in Drive or Reverse, but not sleeping. For exampe, if I get into my car in the morning and turn on the A/C, but don't put it in drive for say, 5 minutes, the energy used to cool down the car is NOT INCLUDED in the energy meter. However, if I put the car into Drive and sit that 5 minutes, most of the energy used to cool the car down IS INCLUDED in the energy meter.

 

[AlanSubie4Life]

Sorry, but I should clearly have said "idling while not in Drive/Reverse". Idling in the sense I was referring to is not the same as idling in a ICE, but time the car is sitting, while not in Drive or Reverse, but not sleeping. For exampe, if I get into my car in the morning and turn on the A/C, but don't put it in drive for say, 5 minutes, the energy used to cool down the car is NOT INCLUDED in the energy meter. However, if I put the car into Drive and sit that 5 minutes, most of the energy used to cool the car down IS INCLUDED in the energy meter.

Thanks for the confirmation. I think this factor is much more likely to explain most of the discrepancy the OP sees (in addition to vampire losses), rather than inaccuracy in the reported kWh draw referenced by @RuiP . They're probably all factors to some extent but probably Idle Losses > Vampire > Inaccuracy.

 

[Olds442]

Thanks. This is my first total EV and I do have a lead foot with this car. It's fun.

well just like an ICE car, a lead foot is less efficient. i'm lucky to get below 300 wh/mi in the P85, i have to try hard to do that. the model 3 seems like it's way more efficient in comparison so you have that going for you.

we can lose 30% of range because we're heat hogs as well as lead footed. the only time i'd worry is on a long trip, where you have to pay a little attention to it. (not much though.)