I think my car is lying to me...

[Brando]

Tip from an old gear head - at 25% in the tank, I starting think about the next fill up - running out of gas a real pain.
(8%? my gas gauge just not that accurate. Hate you electrics with computer/cell phone precision.)

 

[supratachophobia]

Tip from an old gear head - at 25% in the tank, I starting think about the next fill up - running out of gas a real pain.
(8%? my gas gauge just not that accurate. Hate you electrics with computer/cell phone precision.)

That's the beauty of technology. Got 10kw in the tank? That's 29 miles baby and zero means zero.

 

[supratachophobia]

More fun.... Car has announced that charging is complete at 94%

There only problem is that the slider is set to 100%, and it won't accept any more charge. The really interesting part though is that nominal remaining and usable full equal the same number at the moment.

 

[hiroshiy]

As I promised, here's the screenshot of 94% SOC.

So the numbers match. Tesla somehow reduces display SOC by 5% gradually if you continue driving, or suddenly if you park the car at low SOC. By watching these behaviors, IMHO this is by design, not by some bugs, and Tesla seems to allow us only use 95% of SOC to prevent something - possibly being stranded at <5% SOC? Just my guess.

But I think this is not a very good way to communicate the remaining battery energy to us drivers.

 

[supratachophobia]

As I promised, here's the screenshot of 94% SOC.
View attachment 365984
View attachment 365985
So the numbers match. Tesla somehow reduces display SOC by 5% gradually if you continue driving, or suddenly if you park the car at low SOC. By watching these behaviors, IMHO this is by design, not by some bugs, and Tesla seems to allow us only use 95% of SOC to prevent something - possibly being stranded at <5% SOC? Just my guess.

But I think this is not a very good way to communicate the remaining battery energy to us drivers.

Are you 90kwh battery? If so, what revision?

 

[ran349]

As I promised, here's the screenshot of 94% SOC.
View attachment 365984
View attachment 365985
So the numbers match. Tesla somehow reduces display SOC by 5% gradually if you continue driving, or suddenly if you park the car at low SOC. By watching these behaviors, IMHO this is by design, not by some bugs, and Tesla seems to allow us only use 95% of SOC to prevent something - possibly being stranded at <5% SOC? Just my guess.

But I think this is not a very good way to communicate the remaining battery energy to us drivers.

We've seen that there are two different SOC % values, one that is based on the nominal full pack value, and one that is based on the usable full pack value, which is 4 kWh less than the nominal full pack. The dash display shows the usable % value. Even though the nominal and usable will both read 100% at full charge, the usable will drop off to zero faster since it has 4 kWh less to begin with.

 

[hiroshiy]

Are you 90kwh battery? If so, what revision?

100kWh

 

[hiroshiy]

We've seen that there are two different SOC % values, one that is based on the nominal full pack value, and one that is based on the usable full pack value, which is 4 kWh less than the nominal full pack. The dash display shows the usable % value. Even though the nominal and usable will both read 100% at full charge, the usable will drop off to zero faster since it has 4 kWh less to begin with.

It seems you didn't compare 1% and 94%; TM-Spy reported value of 92.7 or 93.6kWh are both usable values, so SOC is also usable % I believe. If you think it is nominal, then I would only be able to use 88-89kWh with my 100kWh pack.

In summary:

At 1% dash SOC
Usable capacity 92.7
Remaining capacity 5.3 (5.7%)
TM-Spy SOC 6.1%

At 94% dash SOC
Usable capacity 93.6
Remaining capacity 88.6 (94.7%)
TM-Spy SOC 94%

At 1%, I assume 5.3kWh does NOT include 4kWh - this is pure usable capacity but my WAG is that Tesla wants to reserve the bottom 5% in a secret way, to prevent sudden loss of power in extreme low SOC conditions.

 

[ran349]

It seems you didn't compare 1% and 94%; TM-Spy reported value of 92.7 or 93.6kWh are both usable values, so SOC is also usable % I believe. If you think it is nominal, then I would only be able to use 88-89kWh with my 100kWh pack.

In summary:

At 1% dash SOC
Usable capacity 92.7
Remaining capacity 5.3 (5.7%)
TM-Spy SOC 6.1%

At 94% dash SOC
Usable capacity 93.6
Remaining capacity 88.6 (94.7%)
TM-Spy SOC 94%

At 1%, I assume 5.3kWh does NOT include 4kWh - this is pure usable capacity but my WAG is that Tesla wants to reserve the bottom 5% in a secret way, to prevent sudden loss of power in extreme low SOC conditions.

You should show the TM-Spy data in table form. It gives values for nominal, usable, and SOC %. That will help with the understanding of what's going on.

 

[Nietschy]

View attachment 365667
View attachment 365668
Let's look at this issue @supratachophobia is pointing out, with just two screenshots. I had a chance to go to 1 percent in my car and the first one is TM-Spy showing 6.1% SOC. The next one is my dash showing 1%. This means there's a discrepancy between TM-Spy report and the dash, which we usually see.

Guess what will happen if you charge above 80%? These numbers match. I will post it once I have a chance to make it above 80%, possibly tomorrow.

What was your dotted power limit before you put it into OFF state?
I get dotted lines at 250kW at about 12% left and less than 100kW at about 3%. Power limit below 80kW means the car may shut down at any time after that. (Tesla Bjorn)

 

[David99]

I did a few more tests and it seems the discharge efficiency varies quite a bit. Between 0.5% to 2.5%.

 

[supratachophobia]

I did a few more tests and it seems the discharge efficiency varies quite a bit. Between 0.5% to 2.5%.

I've noticed it closer to 5-8% off at low states of charge. For example. Under 15%, using 270 watts per mile (or less) instead of the 290 EPA is closer to what I've observed the range remaining using at low states of charge. Not sure if that's what you were trying to say though.

 

[David99]

I've noticed it closer to 5-8% off at low states of charge. For example. Under 15%, using 270 watts per mile (or less) instead of the 290 EPA is closer to what I've observed the range remaining using at low states of charge. Not sure if that's what you were trying to say though.

I'm definitely seeing the same thing that you described overall. The car counts rared miles down faster than the numbers add up to. That's definitely happening. The discrepancy between energy in the battery and energy taken out at the end of a trip is just expected inefficiency in the discharge process. I don't know where and how much it plays into the problem. It seems Tesla doesn't account for it when showing you rated range when the battery is fully charged.

 

[ran349]

I'm definitely seeing the same thing that you described overall. The car counts rared miles down faster than the numbers add up to. That's definitely happening. The discrepancy between energy in the battery and energy taken out at the end of a trip is just expected inefficiency in the discharge process. I don't know where and how much it plays into the problem. It seems Tesla doesn't account for it when showing you rated range when the battery is fully charged.

I think that is the main takeaway from all the discussions here. For example, my car consumes rated miles at 270 Wh/mi when I am driving. It is the same regardless of the charge percentage of my battery. But I recharge my battery at 287 Wh/mi, as I have confirmed with a lot of data I have taken. That amounts to a charge/discharge efficiency of 270/287 = 94%. This is not accounted for in the rated range calculation, as you said.

 

[David99]

I think that is the main takeaway from all the discussions here. For example, my car consumes rated miles at 270 Wh/mi when I am driving. It is the same regardless of the charge percentage of my battery. But I recharge my battery at 287 Wh/mi, as I have confirmed with a lot of data I have taken. That amounts to a charge/discharge efficiency of 270/287 = 94%. This is not accounted for in the rated range calculation, as you said.

Yes the car actually keeps track of this. On the CAN bus data you can see the lifetime total energy charged and discharged. There is about a 6-7% difference. As far as I can tell the discharge efficiency is a little better. 2 % losses when discharging, 4% losses when charging. I don't think the charging losses inside the battery are contributing to the range difference we are seeing. The BMS reports how much energy the battery can store, not how much needs to be charged. The capacity is what's the basis for the rated range calculation. Based on my (admittedly limited tests) I see quite a difference in how high the losses are. Probably caused by temperature, state of charge, charge/discharge rate and possibly other factors. The BMS can't predict ahead of time what the conditions will be.

I still believe that the major factor that causes the range to be less than what the car tells us is due to the protecting buffer at the bottom. The BMS takes the entire capacity and then gradually counts faster to arrive at the point where it's at 0% usable.

 

[ran349]

Yes the car actually keeps track of this. On the CAN bus data you can see the lifetime total energy charged and discharged. There is about a 6-7% difference. As far as I can tell the discharge efficiency is a little better. 2 % losses when discharging, 4% losses when charging. I don't think the charging losses inside the battery are contributing to the range difference we are seeing. The BMS reports how much energy the battery can store, not how much needs to be charged. The capacity is what's the basis for the rated range calculation. Based on my (admittedly limited tests) I see quite a difference in how high the losses are. Probably caused by temperature, state of charge, charge/discharge rate and possibly other factors. The BMS can't predict ahead of time what the conditions will be.

I still believe that the major factor that causes the range to be less than what the car tells us is due to the protecting buffer at the bottom. The BMS takes the entire capacity and then gradually counts faster to arrive at the point where it's at 0% usable.

The 6-7% difference you show between charging and discharging is the amount I see in my actual driving Wh/mi for rated range vs. the calculated Wh/mi for rated range. So your data is consistent with what I have observed.
I don't think the protection buffer is the cause of the difference because that buffer is never used (if it really is for protection). I have a feeling Tesla doesn't show that protection buffer in the BMS data, but we don't know for sure.

 

[David99]

The 6-7% difference you show between charging and discharging is the amount I see in my actual driving Wh/mi for rated range vs. the calculated Wh/mi for rated range. So your data is consistent with what I have observed.
I don't think the protection buffer is the cause of the difference because that buffer is never used (if it really is for protection). I have a feeling Tesla doesn't show that protection buffer in the BMS data, but we don't know for sure.

The buffer is in the BMS data. It shows a 4 kWh buffer. It shows total capacity and usable capacity. I posted about it here: This is why you can't get 'rated range'

The numbers show that Tesla is using the entire battery capacity to calculate range, but then count down rated miles 'faster' to arrive at zero just when the buffer is reached. To hide it, it does so gradually over the entire discharge.

 

[ran349]

The buffer is in the BMS data. It shows a 4 kWh buffer. It shows total capacity and usable capacity. I posted about it here: This is why you can't get 'rated range'

The numbers show that Tesla is using the entire battery capacity to calculate range, but then count down rated miles 'faster' to arrive at zero just when the buffer is reached. To hide it, it does so gradually over the entire discharge.

But the problem is, the EPA test determines what the rated range is, which is actual miles driven on a full charge, and that doesn't include the buffer.

 

[ChadFeldheimer]

Thanks to all the contributors to this thread. Interesting findings.

Regarding battery discharge inefficiency: Does the degree of inefficiency vary? For example, depending on rate of discharge or perhaps the temperature of the cells during discharge. On the face of it, it seems a bit lame to advertise battery capacity that can never be utilized. But maybe it is acceptable if the energy available is not known until (some of) it has been used.

On the other hand, rated range ought to be range that you can achieve at the given rated efficiency. Anything else is, at best, incompetent - whether it arises from discharge inefficiency or advertising the use of an unusable reserve.

Follow up question: should we expect discharge inefficiency to change with battery health / aging?

 

[hiroshiy]

What was your dotted power limit before you put it into OFF state?
I get dotted lines at 250kW at about 12% left and less than 100kW at about 3%. Power limit below 80kW means the car may shut down at any time after that. (Tesla Bjorn)

I don't think it's relevant but the second screenshot was in OFF state (you can at least read OFF text there) with completely warmed battery. So no dotted lines.