Discrepancy between Charge Spent vs Charge needed to get back to same level

[animonj]

I have this interesting observation and I am not able to reconcile all the data

• I had a starting charge of 70%, drove 60+ miles, and came back with a 45% charge remaining.
• Tesla Trips screen showed that I drove 61 miles and used 17kWh, average 276Wh/mi
• Immediately after reaching back, I charged back to 70%, and the Tesla app showed that 70% charging was completed, and used 22kWh

Discrepancies

1. Per the stats shown Tesla Trips screen, I used 25% of the charge capacity (70%-45%), hence derived total capacity is 68 kWh (17 / (25/100) )
2. Per the Tesla app, it took 22kWh to go from 45% to 70%, and hence derived total capacity is 88 kWh (22 / (25/100) ). this doesn't match with the first calculation or the data available elsewhere (75kWh)
3. Why does it show a loss of 17kWh to go from 70% to 45% and require 22kWh to go from 45% to 70%?

 

[GtiMart]

A couple points to help you. First, the trips screen only shows the energy used while you are in Drive. You also consume energy while in Park sitting in the car, like the AC running for example. You also consume energy when you're not in the car, either using Sentry mode, cabin overheat protection, keep climate on etc. Even sleeping the consumption isn't quite zero. All of that consumption is not reflected anywhere in the trips screen but it's energy that was taken out of your battery.
Second, there are losses in charging. Not all the energy that the charger delivers ends up in the battery. The charging equipment isn't 100% in the conversion, and you are also running the car's computer and coolant pump as you charge which probably consumes 200-250w.

EDIT: Also, the kWh numbers are clearly rounded, maybe up or down, don't assume they are precise.

 

[animonj]

thanks, @GtiMart for the reply. to clarify some points

1. Sentry mode was not used.
2. the whole trip was about 2 hours, 80 minutes driving, and 40 mins waiting
3. I didn't receive any cabin overheat protection notification. The car was parked in a shaded area
4. The charge used was reported by Tesla app, it was charged at home, not at supercharger. so I have no idea how much energy was pushed, only that Tesla reported using 22Kwh, assuming this is being reported from the receiving end.
5. Air condition was used, temp was set to 72. the overall consumption 25% should include this. not sure if the 17kWh includes that,
6. I started charging immediately after reaching home. charged for 2 hours and 45 mins. so it took about 5 hours between when I started with 70% charge and finished with 70%. not much time to account for leakage while parked.
7. Tezlab reported that 20.9kWh energy was drawn to fill 20kWh (95% efficiency), these figures also differ from Tesla's reported figure of 22kWh

even after the rounding issues and parking were accounted for, the discrepancy is about 17-30% based on the 17kWh. I wish Tesla is more forthcoming with data and more honest and transparent with the range.

 

[GtiMart]

Your 40 minutes of waiting... Were you in the car sitting with ac on? That can take a good couple kwhs. Tesla isn't hiding anything. As with ice cars the trip reports what the trip consumed.

 

[animonj]

No one was in the car, it was locked and the AC was not working and as i said before no overheating protection notification was received. My issue is with numbers not adding up. For ICE cars, if the claim is 22mpg, over a period of time, may be 2000+miles, i will get 22 or above mpg. Not with Tesla, i don't get even 70% of the published mileage, on top of it, i see all kind of discrepancy in the charging numbers. 17 spent, 22 charged per Tesla, 20 per Tezlab. With 328 published range, i cannot travel more than 150 miles relying on supercharging stations. With the way supercharging prices have been increased, driving long distance in Tesla is not an option. Frequent stops, price similar to gas prices, and range anxiety. Overall, my Tesla honeymoon is over

 

[ucmndd]

17 spent, 22 charged per Tesla, 20 per Tezlab.

Yes. Expect about 15% loss between electricity coming out of the wall and ending up at the wheels for propulsion.

All of that AC-DC-AC conversion is not free. Your car’s wiring is not a super conductor so there are resistance losses too. Physics sucks that way.

 

[animonj]

Yes. Expect about 15% loss between electricity coming out of the wall and ending up at the wheels for propulsion.

All of that AC-DC-AC conversion is not free. Your car’s wiring is not a super conductor so there are resistance losses too. Physics sucks that way.

Focus on the issue here, not the non issue of charge efficiency. Per Tezlab, 20.9kwh was usedTo charge 20kwh. Tesla doesn't show details of the 22kwh figure. Even assuming this is the charge drawn, the charge reached should be 20.9 based on the Tezlab figures. The issue is the discrepancy between the charge used vs recharged quantity. They don't match

 

[ucmndd]

Focus on the issue here, not the non issue of charge efficiency. Per Tezlab, 20.9kwh was usedTo charge 20kwh. Tesla doesn't show details of the 22kwh figure. Even assuming this is the charge drawn, the charge reached should be 20.9 based on the Tezlab figures. The issue is the discrepancy between the charge used vs recharged quantity. They don't match

There is no issue. At least not one that you’re going to solve and arrive at a satisfactory answer. If you’re looking for to-the-fraction-of-a-kWh accuracy in the energy consumption meter, you’re going to be perpetually disappointed.

Analogy - the fuel economy meter in my ICE car is perpetually optimistic by about 10%. If it says I got 32.5 mpg to the tank, my measurement at the pump is more like 30mpg flat.

I can bang my head against the wall about this, or I can just drive.

 

[LoneStarEve]

Tezlab is incorrect.

If you add 20kWh to your battery you will get about 80% efficiency using the on-board charger at high L2 amperage.
So if for example, not your numbers, 20kWh was put into the battery then 25kWh was more like the figure pulled from the wall.
If you use L2 charging the efficiency is even worse.

The car says you used 17kWh to drive the 60 miles. i.e. you pulled 17kWh out of the battery to do it.
It says charging it back up consumed 22kWh.
80% of 22kWh is 17.6kWh.
Which is close to the 17kWh it says you used to do the trip.
No mystery.

 

[animonj]

Tezlab is incorrect.

If you add 20kWh to your battery you will get about 80% efficiency using the on-board charger at high L2 amperage.
So if for example, not your numbers, 20kWh was put into the battery then 25kWh was more like the figure pulled from the wall.
If you use L2 charging the efficiency is even worse.

The car says you used 17kWh to drive the 60 miles. i.e. you pulled 17kWh out of the battery to do it.
It says charging it back up consumed 22kWh.
80% of 22kWh is 17.6kWh.
Which is close to the 17kWh it says you used to do the trip.
No mystery.

this makes sense, but it would have been nice if the information was more clearly presented.
1. is 80% the published efficiency rate for at-home charging using Gen 2 NEMA Adapter 14-50 (240V)? It looks like a lot of people have reported 80% charging efficiency
2. calculating the charge consumed from the data shown for Average efficiency and total miles, 0.276 * 61 =16.84 kWh. so the efficiency I am getting is lower than 80% (16.86/22=76.64%)

 

[Empiro]

Question: what was the battery percentage when you got back in your car? I've found that if the car adjusts the battery level, it shows up as extra or lower energy added. I've had several times where after charging, the battery increases or decreases by several percent, and it always causes the energy added to change.

Working strictly off battery percentage and the battery size of the Y (around 80kwh) 25% comes out to 20 kWh added, which tracks with your app that reported 20.9 kWh added. Then if the battery was adjusted up 3%, it would come out to 22 kWh added.

The above scenario tracks best with what you reported:

Your drive consumed about 17 kWh as reported by the car. It didn't use much energy past that since you had sentry turned off and the car was kept cool. However, for whatever reason, the BMS thought you had a lower battery percentage, accounting for the 3 kWh or so "missing". You then charged for 20 kWh, which brought you above what you started off your trip with. After a time, your car notices that the battery level is higher and adjusts it upwards.

 

[animonj]

Question: what was the battery percentage when you got back in your car? I've found that if the car adjusts the battery level, it shows up as extra or lower energy added. I've had several times where after charging, the battery increases or decreases by several percent, and it always causes the energy added to change.

Working strictly off battery percentage and the battery size of the Y (around 80kwh) 25% comes out to 20 kWh added, which tracks with your app that reported 20.9 kWh added. Then if the battery was adjusted up 3%, it would come out to 22 kWh added.

The above scenario tracks best with what you reported:

Your drive consumed about 17 kWh as reported by the car. It didn't use much energy past that since you had sentry turned off and the car was kept cool. However, for whatever reason, the BMS thought you had a lower battery percentage, accounting for the 3 kWh or so "missing". You then charged for 20 kWh, which brought you above what you started off your trip with. After a time, your car notices that the battery level is higher and adjusts it upwards.

I will keep an eye on this, i don't think I took a screenshot when i started the car next time, it is possible that the car charged 2-3% more than it needed to reach 70% though the screenshot from the app showed that after charging the SOC is 70%.

the recent charging did not show this issue. taking the 80% charging efficiency rule, I came back with 37% SOC, trip meter showing 81 miles using 23kWh and charging shows 26kWh used for charging. 23/26 is around 88% efficiency. so, the issue could be as you described, car understimated and overshot the 70% threshold set.