Wh / Mile vs Actual electricity draw 50% discrepancy

[muncheroo]

Hi Everyone,

Just reached first 1000 miles so I checked my stats.

I'm averaging about 400Wh/mile so theoretically after 1000 miles, I should be at 400kWh of electricity used.

I have a meter attached to my charging outlet and it's at 601 kWh, about 50% more than expected.

Just wondering if anyone else ever studied their actual electricity draw and if this is within the realm of normal.

 

[muncheroo]

Hm seems like it’s just a case of bad vampire drain after doing some more reading.

 

[DCGOO]

Hi Everyone,

Just reached first 1000 miles so I checked my stats.
I'm averaging about 400Wh/mile so theoretically after 1000 miles, I should be at 400kWh of electricity used.
I have a meter attached to my charging outlet and it's at 601 kWh, about 50% more than expected.
Just wondering if anyone else ever studied their actual electricity draw and if this is within the realm of normal.

1,000 miles is not really enough to represent much, especially the first 1000. But it sounds pretty normal to me. The 400Wh/mile represents the rate at which energy is being consumed while driving. Energy consumed while parked or charging can be quite a bit more and is not counted in the 400 from the energy graph.

 

[mxnym]

Energy consumed while parked or charging can be quite a bit more and is not counted in the 400 from the energy graph.

There is also efficiency loss in ANY conversion, and conversion from AC to DC is necessary to charge.

 

[ajdelange]

The charger is not 100% efficient. I have seen charge efficiencies of from 87 - 100.8%. Yes, greater than 100% but that is clearly due to rounding error of something of the sort. That would explain a 10% discrepancy but not 50. I'd start with checking the power meter against a known load (like an electric heater).

Then I would look at the trip indicators. They show the total miles and the total kwHr consumed. Use that for your comparison i.e. compare what the trip indicator said you used to what the watt meter says. Obviously you will get the most meaningful result if you have not reset the trip accumulaors. Many people apparently never reset one of them over the life of the car. If you have reset one then in the past then reset it again, reset the watt meter at the same time and then compare over some period of time.

FWIW TeslaFi said I used 7.9 kWhr on the last charge and a watt hour meter connected to the line said I used 8.16. That's about a 3 % difference. OTOH when TeslaFi said I had 100.8 charging efficiency the difference between what it said I used and what the watt hour meter said were much more disparate than 3% so clearly what the car is reporting to TesliFi and/or how TesliFi interprets it can be prone to error.

 

[fbitz777]

To give you my experience on my X75D:

Takes 82kwh on my electrical meter to charge (0-100 percent)...

Drive and get about 200miles in ideal conditions and close to rated down to zero and Tesla shows I used 65kwh.

so YES there is a discrepancy....65/82 is more like 20 percent. It's much worse now in the cold though!

AND I am not counting the 2-3 kwh lost every day I leave he car idle...Vampire Drain.

 

[David99]

50% is a lot, but it can be explained. I have had access to the CAN bus of my car for about 3 years now and have been able to log detailed info.

First of all, the on board chargers are aprox 85-90% efficient. IOW you are losing about 10-15%. The wiring and cables from your electricity meter to the car also have some losses. Depending how long it is, it can be 5-10%.
The car's energy meter only counts energy used while the car is moving. Any energy used while it's parked is not accounted for. Any preconditioning, base load, HVAC during idling and 'vampire drain' and so on doesn't show up. The less a car gets used, the more it stands and the more are those idle losses that don't show up in the car's energy consumption display.
The battery itself also has some losses. In fact Tesla keeps track of the battery efficiency by counting energy going in separately from energy going out. In my car there is a total of aprox 7% loss.

All these things together can add up to 50%. Nothing wrong with your car.

 

[fbitz777]

Should you not say 33% discrepancy? you are still getting 66% of what you put in (not 50 percent).

Now if you were driving at 300wh/mi (close to the rated for X and easy in nice weather) your discrepancy would be 20% assuming you don't stop or overnight drains.

This is one one my biggest issue with how Tesla gets away with under reporting consumption unless you use a CAN bus reader. The Bolt EV does not have that problem. On the Bolt the under reporting is only 10 percent ..i.e the loss from the battery charger.

 

[ajdelange]

Any energy used while it's parked is not accounted for. Any preconditioning, base load, HVAC during idling and 'vampire drain' and so on doesn't show up.

Not so. Those loads do get counted. I verified that again just this evening.

 

[fbitz777]

Not so. Those loads do get counted. I verified that again just this evening.

He is talking about what's displayed on the Tesla screen and he is correct in that these loads are not shown..Try to park and sit in the car, the consumption does not go up on the screen
Maybe you are referring to Teslafi reporting all of these correctly and then you are right.

 

[David99]

Not so. Those loads do get counted. I verified that again just this evening.

Put your car in Park. Look at any trip numbers. Energy amount and or Wh/mile. Now turn on the heater full blast and let it run for a while. Look at the numbers. They do not change. The trip meters do not count energy used while the car is standing. The trip meters are the only way to look at the total energy consumption of the car. At least on the UI. You can look at the CAN bus data to see the actual energy usage while the car is parked as well.

PS: no the car does not 'catch up' once you start driving again. The range will correctly account for the used energy. The range number will drop down as energy is used even when the car is standing. But again, this is not reflected in any trip numbers.

 

[ajdelange]

Err, yes they are. I saw it with my own eyes tonight. Well, let me be precise. They appeared on the little screen above the steering wheel. I also believe they appear on the main screen as whenever I start out after sitting in the car with heater on the intial Wh/mi shows a huge spike.

 

[ajdelange]

Put your car in Park. Look at any trip numbers. Energy amount and or Wh/mile. Now turn on the heater full blast and let it run for a while. Look at the numbers. They do not change.

That's exactly what I did. True the numbers will not change until you put the car in drive and start to move. As soon as you have moved some distance less than 0.1 miles the trip meters jump by much more than it takes to drive the distance required to start reporting. I went a couple of hundred feet and the kWhr jumped 300. The whr/mi number jumped to over 6000.

The trip meters do not count energy used while the car is standing. The trip meters are the only way to look at the total energy consumption of the car.

I'm pretty confused. It seems to me those two sentences contradict one another. Looks as if the second one is true and the first false.

PS: no the car does not 'catch up' once you start driving again. The range will correctly account for the used energy. The range number will drop down as energy is used even when the car is standing. But again, this is not reflected in any trip numbers.

Again, that conflicts with what I saw tonight ipse oculis meis.

There is uncertainty in my mind about when the "Since hh:mm" trip meter starts accumulating but it would be very misleading for the "Since Last Charge" meter to list kWhr when that is not what the display is actually showing. Again, the display does not update until the vehicle starts moving but from what I can see it does accumulate.

 

[ajdelange]

Another observation from tonight and one I had forgotten to mention: while sitting in park with the heater on I noticed that the kW meter is reading slightly above 0 as, of course it should but I had never noticed that it did before.

Could this and the other discrepancies with what everyone seems to accept be due to different firmware? I have 2018.48.12.1 d6999f5. According to a message from TelaFi 50.6 is out there. Or am I not seeing what I think I'm seeing?

 

[David99]

Trust me when I say the trip meters stop counting when the car is not moving. I have looked at the CAN bus data parallel to what the car shows in any of the trip meters. Every time I stop I can see the car's trip meters stop counting energy while on the CAN bus I can see exactly how much energy is used. Park your car for several days and your car will use a lot of energy. Aprox 2-3 kWh a day. It will not show up in any trip meter. If will show up as lost range, though.

The range, how many miles you have left, will always update. It might sound contradicting, but that's just how the car works. Not saying it makes sense but that's how it works. The range always has to be based on the remaining energy in the battery. So the car has to count any energy taken out or added to be able to accurately calculate remaining range. The trip meters work like many trip meters in many other cars do. They stop counting when you stop driving.

So going back to the OP, what we have to look at in terms of how much energy we have used is any of the trip counters. As the OP said, he looked at the total energy the trip meter showed. That number is only energy used while driving. Any energy used while parked or stopped is not counted in the trip numbers.

 

[David99]

Should you not say 33% discrepancy? you are still getting 66% of what you put in (not 50 percent).

Now if you were driving at 300wh/mi (close to the rated for X and easy in nice weather) your discrepancy would be 20% assuming you don't stop or overnight drains.

This is one one my biggest issue with how Tesla gets away with under reporting consumption unless you use a CAN bus reader. The Bolt EV does not have that problem. On the Bolt the under reporting is only 10 percent ..i.e the loss from the battery charger.

The EPA test method actually measured energy consumption at the grid. So all energy used by the car and charge inefficiencies are included in the EPA test cycles. The EPA only tests 15% of all cars themselves, though. 85% is done by the car manufacturer and then just reported to the EPA. So there is some wiggle room LOL

 

[mswlogo]

Trust me when I say the trip meters stop counting when the car is not moving. I have looked at the CAN bus data parallel to what the car shows in any of the trip meters. Every time I stop I can see the car's trip meters stop counting energy while on the CAN bus I can see exactly how much energy is used. Park your car for several days and your car will use a lot of energy. Aprox 2-3 kWh a day. It will not show up in any trip meter. If will show up as lost range, though.

The range, how many miles you have left, will always update. It might sound contradicting, but that's just how the car works. Not saying it makes sense but that's how it works. The range always has to be based on the remaining energy in the battery. So the car has to count any energy taken out or added to be able to accurately calculate remaining range. The trip meters work like many trip meters in many other cars do. They stop counting when you stop driving.

So going back to the OP, what we have to look at in terms of how much energy we have used is any of the trip counters. As the OP said, he looked at the total energy the trip meter showed. That number is only energy used while driving. Any energy used while parked or stopped is not counted in the trip numbers.

The meters are running when it’s stopped. But they stop running when it’s in park.

All pre heating is not accounted for.

 

[ajdelange]

Trust me when I say the trip meters stop counting when the car is not moving.

So then how do we explain the jump of 0.3 kw over a distance of 300' at 10 mph? Is something broken? Do I need to take the car in for service?

 

[David99]

So then how do we explain the jump of 0.3 kw over a distance of 300' at 10 mph? Is something broken? Do I need to take the car in for service?

Sample intervals are creating completely useless results for anything less than a minute or a mile. For the numbers to have any meaning you need to drive a few miles.

 

[Kant.Ing]

That Wh/mi shows only the energy consumption of moving the car.