I don't observe that at all. My consumption rate is constant from full charge down to 15%. I have never gone lower than that, but there is a lot of uncertainty when you get down that low.
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I think my car is lying to me...
- Thread starter supratachophobia
- Start date
I don't observe that at all. My consumption rate is constant from full charge down to 15%. I have never gone lower than that, but there is a lot of uncertainty when you get down that low.
I still think that even the batteries aren't created equal. I think the 70kw battery behaves differently than the 90kwh batteries.
I though so, I think @hiroshiy was referring to SOC % when they mentioned "Tesla dash percentage".
If SOC is based on Amp Hours (which it should be), then it will drop faster as the pack voltage drops and the current increases to maintain the same kW rate.
Fact is, when I drive exactly at the rated consumption, I will not get rated range. I will get noticeably less. I have tested this. The numbers from the CAN bus show the same.
Yes, I think anyone who has tested their own car would agree with you. I think it's because that rated consumption number is not taking into account the charge and discharge losses. You had said earlier that the charging losses were around 4%. How did you calculate that from the CAN bus data?
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This is why you are incorrect. If you can agree different driving styles would produce different inefficiencies (I think we can agree on that). Then take a look at the consumption since last charge. The ratio of EPA consumption/actual consumption, will *always* match the ratio of 100% miles remaining/actual miles driven. This is regardless of your driving 50% over/under EPA consumption which would produce very different efficiency loses/gains. Not sure if I explained that the right way.
It was hard to follow what you just said, but if I understand you correctly, then I disagree with your statement. Using my own car for exampe, if I drive at EPA consumption of 290 Wh/mi, then my actual driven miles are about 90% of my rated miles used. If I drive at 270 Wh/mi, then my actual driven miles are 100% of my rated miles consumed. If I drive at 320 Wh/mi, then my actual miles are 80% of my rated miles used. Is that what you mean?
First, rational two-way dialog between disagreeing parties is awesome.
Maybe we can come to a consensus on this. Using your car as an example, 270 watts per miles is your EPA consumption (or rather, the number that Tesla has assigned to your battery that matches with what's on your dashboard at 100% given the available energy available). I think what you are saying is that you can actually go the dash rate miles if you use that 270 consumption number, from 100% right down to zero, you'll hit it. And if you couldn't hit it, like myself, then you are suggesting that there are losses in the drive-train and the extraction of energy from the battery, weather through the DC to AC conversion, heat, friction, etc. The end result is that I come up short.
What I am suggesting is that your point about the conversion losses is very valid. And in your solution, depending on how much you exceeded your 270 number, the losses at the end of the battery would vary. Discharging the battery at higher rates is less efficient, isn't it? So by that logic, you would be off by not only the percentage loss, but an additional amount to account for the higher, less efficient discharge rate? In other words, the difference would be unpredictable because we don't know the efficiency losses at each discharge level.
But in my case, I'm saying that the ratios are the exact same, and therefore don't account or allow for any other corrections. If I exceed the consumption by 20%, I reduce the available miles driven by 20%. The ratios are locked. And at the end of a discharge cycle, the only number that fits both equations and both corrections (+/- EPA consumption) is the usable capacity of the battery, not the nominal.
I have a super fun fact to share. If I charge to 100% and then drive the car down to less than 15, I can repeat this every single time now.
Arrive to destination with 9.93% remaining (dash says 10%).
Nominal Full: 76.5
Nominal Remaining: 11.2
Usable Full: 72.5
Usable Remaining: 7.2
The *only* way to get 9.93 is to take Usable Remaining divided by Nominal Full.
**wait** one hour, no HVAC, app access, or use of any kind.
Walk up to car and read BMS; 4.82% remaining (dash says 5%). Where did that 5.11% go???
Nominal Full: 76.6
Nominal Remaining 7.5
Usable Full: 72.6
Usable Remaining: 3.5
The *only* way to get 4.82.... is to take Usable Remaining divided by Usable Full.
Once the car has a chance to catch it's breath, it changes it's algorithm. And I can see it happen in the hard data.
Arrive to destination with 9.93% remaining (dash says 10%).
Nominal Full: 76.5
Nominal Remaining: 11.2
Usable Full: 72.5
Usable Remaining: 7.2
The *only* way to get 9.93 is to take Usable Remaining divided by Nominal Full.
**wait** one hour, no HVAC, app access, or use of any kind.
Walk up to car and read BMS; 4.82% remaining (dash says 5%). Where did that 5.11% go???
Nominal Full: 76.6
Nominal Remaining 7.5
Usable Full: 72.6
Usable Remaining: 3.5
The *only* way to get 4.82.... is to take Usable Remaining divided by Usable Full.
Once the car has a chance to catch it's breath, it changes it's algorithm. And I can see it happen in the hard data.
If that was the case the discrepancy would be different for different conditions. The charge and discharge inefficiency varies (based on my measurements). The missing part is not changing though. It is very consistent. Also it makes no sense as the range that is shown to the driver is clearly calculated based on the nominal capacity in the battery. That means charge inefficiencies cannot be part of the equation. It is very consistent and always exactly comes down to the difference of the buffer.
The CAN bus shows 'nominal capacity' which is the total amount of energy in the battery. Take that number and divide it by the rated consumption and you end up exactly what the car shows as rated range when fully charged. But since 'usable capacity' = 'nominal capacity' - 4 kWh the range you are getting is less. It is always exactly 4 kWh less. The numbers are so clear. The rated range display gradually shifts from nominal capacity to usable capacity as the battery is discharged.
My car definitely doesn't show a jump down, rather it shifts gradually (as I drive) from using the entire capacity as the basis to using the buffer point as a basis. That seems to be the exact same behavior that Jason described in one of his posts.
I know what you are saying now, and we are not on the same page yet, but maybe we can get there.
First minor point- my EPA consumption number is 290, not 270. But I have to drive 270 Wh/mi to get rated miles equal to driven miles, which is similar to what others report. I never get rated range at 290 Wh/mi, even though the energy graph tells me that I should.
The losses I am referring to are the internal battery losses that are not directly measured by the BMS from the battery when discharging, or to the battery when charging. Some are resistive losses but some are related to the battery chemical reactions during charging and discharging.( I am not a battery expert so I'll stop there). I don't think these discharge losses are changing too much under typical variations of normal driving conditions, say from 270 to 330 Wh/mi, so the percent differences you are talking about due to different discharge rates would be relatively minor. My charging efficiencies are extremely consistent at 287 Wh/mi +/- 1 Wh/mi.
The *only* way to get 9.93 is to take Usable Remaining divided by Nominal Full.- Incorrect
Usable remaining divided by Usable Full = 7.2/72.5 = 9.93%
Usable remaining divided by Nominal Full = 7.2/76.5 = 9.41 %.
The *only* way to get 4.82.... is to take Usable Remaining divided by Usable Full.-Correct
Could you provide actual or estimated CAN bus numbers from your own car to look at?
What I would like to see is based on assumption that you had driven your car down to 0% on the dash:
1) After fully charging back to 100%, what would your nominal full pack value be?
2) What would your full rated range be in miles?
3) How many kWh would the CAN bus report you had added back to the battery? I am assuming this is the same as the value that the dash reports after charging but without any decimal place precision. Is that correct?
I can probably dig up those numbers for you.
1. 76.5
2. 269
3. Just did this last week, 72kw*
I'll get you the CSV file though.
*Not sure how accurate this is, my car won't charge to 100% sometimes. This was 95% according to the bms.
You are totally correct on this. I might be troubleshooting two problems here now.
Hi, I'm not talking about consumption rate - I was talking about SOC % being decremented non-linear... it reduces faster as the battery is getting discharged.
I don't think the dash is displaying amp hours; then why does SOC% deeply correlates to the consumption rate, which is denominated in watt hours, not amp hours?
As you already know the battery voltage changes from 400 to approx 330 which is a big change.