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Parked at 50% SOC... shows 54% SOC 30 mins later without being plugged in?
- Thread starter Mechsmoto
- Start date
E90alex
Active Member
The BMS can only guess at the charge level until it gets a chance to read the actual cell voltages. Eg when it’s at rest. Sometimes it goes up. Sometimes it can go down.
10/4 on that! I just wish I knew what the actual degradation is. If it's 150 miles at 50% it's minimal... 5% +/-. If it's genuinely 141 miles @ 50% SOC 282/315 is closer to 10%.
5-10 percent fine for now... but what happens when it's showing 15-30 percent degradation in its calculations.
Should it be swapped or not be swapped kinda thing if that makes sense.
5-10 percent fine for now... but what happens when it's showing 15-30 percent degradation in its calculations.
Should it be swapped or not be swapped kinda thing if that makes sense.
E90alex
Active Member
It’s not 150 at 50%. It was 150 at 54%. 50% was 141. The miles displayed is strictly a % of the 100% range.
But that’s not really an accurate way to gauge degradation anyways. There’s too much rounding error to make a fuss about a few miles difference.
It could have been 150.4 miles at 53.5%. Or it could have been be 149.5 miles at 54.4%. That comes out to a calculated 281.1 mi at 100% vs 274.8 mi.
Second, the BMS may be out of calibration and not showing accurate numbers.
But that’s not really an accurate way to gauge degradation anyways. There’s too much rounding error to make a fuss about a few miles difference.
It could have been 150.4 miles at 53.5%. Or it could have been be 149.5 miles at 54.4%. That comes out to a calculated 281.1 mi at 100% vs 274.8 mi.
Second, the BMS may be out of calibration and not showing accurate numbers.
I think you're too busy trying to shut me down to actually open your mind and think into what I'm saying.
I never plugged in the car. When I arrived home it showed 50% and 141 miles. Without any changes or the car being plugged in. The SOC changed to 54%.
The BMS originally estimated there was 141 miles at the same SOC... Again, the car was not plugged in. Simply by sitting and balancing itself out... the battery then had more available capacity than the BMS originally calculated.
Instead to raise the percentage to match it's estimation. It should be able to adjust it's estimation to match the actual capacity that is available.
This has to make sense! No energy was added. Yet, there were more available miles at a given SOC than the BMS thought!
The correct way to address that is to recalculate capacity... and understand that it actually has 150 miles available at that given SOC vs changing the SOC to incorrectly match it's miscalculated answer.
I never plugged in the car. When I arrived home it showed 50% and 141 miles. Without any changes or the car being plugged in. The SOC changed to 54%.
The BMS originally estimated there was 141 miles at the same SOC... Again, the car was not plugged in. Simply by sitting and balancing itself out... the battery then had more available capacity than the BMS originally calculated.
Instead to raise the percentage to match it's estimation. It should be able to adjust it's estimation to match the actual capacity that is available.
This has to make sense! No energy was added. Yet, there were more available miles at a given SOC than the BMS thought!
The correct way to address that is to recalculate capacity... and understand that it actually has 150 miles available at that given SOC vs changing the SOC to incorrectly match it's miscalculated answer.
E90alex
Active Member
No you’re not understanding. Stop thinking about it in terms of miles.
You’re correct that no energy was actually added. It mistakenly thought it had 50% of energy in the battery. Again, it cannot measure cell voltages while in use (charging/discharging) so it can only estimate it. After resting and remeasuring cell voltages, it found out it actually had 54%. It simply estimated wrong in the beginning to get 50%. It didn’t find more energy.
You’re correct that no energy was actually added. It mistakenly thought it had 50% of energy in the battery. Again, it cannot measure cell voltages while in use (charging/discharging) so it can only estimate it. After resting and remeasuring cell voltages, it found out it actually had 54%. It simply estimated wrong in the beginning to get 50%. It didn’t find more energy.
Awesome discussion! Thanks so much for being willing to bounce ideas back and forth.
I hear what you're saying, and in theory... it should be what youre describing.
Thing is, I'm super OCD on the miles thing. I can assure you that once the BMS decides for example... 282 is full charge. 50 percent of that will always be 141.
The BMS makes its adjustments based on many things I'm sure. But it is directly related to the miles.
Point being, when I arrived home it saw 141 and showed 50% SOC because that is exactly half of what it's expecting the total capacity to be.
Please keep following me here. Once it settled, it realizes it doesn't have 141 miles worth of energy available. It actually has 150 miles worth of energy available.
Instead to just stay at 50% SOC and allow the miles to change. It stays stuck on there can only be 141 at 50% SOC and increases that number instead.
I hear what you're saying, and in theory... it should be what youre describing.
Thing is, I'm super OCD on the miles thing. I can assure you that once the BMS decides for example... 282 is full charge. 50 percent of that will always be 141.
The BMS makes its adjustments based on many things I'm sure. But it is directly related to the miles.
Point being, when I arrived home it saw 141 and showed 50% SOC because that is exactly half of what it's expecting the total capacity to be.
Please keep following me here. Once it settled, it realizes it doesn't have 141 miles worth of energy available. It actually has 150 miles worth of energy available.
Instead to just stay at 50% SOC and allow the miles to change. It stays stuck on there can only be 141 at 50% SOC and increases that number instead.
E90alex
Active Member
We’re just going I circles here. The miles displayed is just a calculated number from SOC %. There is no way to increase the miles without increasing the SOC unless the 100% charge mileage has changed.
Yes it recalculated that it had “150 miles” of energy available. Which translates to 54%.
Yes it recalculated that it had “150 miles” of energy available. Which translates to 54%.
E90alex
Active Member
Think of an 8 oz cup of water. If you simply look at it and estimate it’s 50% full, that means it should have 4 oz of water in it.
But now you actually go and measure the volume of water and it’s actually 4.32 oz of water. It does not mean that now 4.32 oz of water is 50% full. It means that the cup was actually 54% full and not 50%.
But now you actually go and measure the volume of water and it’s actually 4.32 oz of water. It does not mean that now 4.32 oz of water is 50% full. It means that the cup was actually 54% full and not 50%.
You're still not getting where I'm coming from.
You're example of 8oz would work.... iffff our capacity wasn't always decreasing.
4 oz was 50% on day one. But 50% is no longer 4 oz at 50,000 miles. Again, this has to make sense.
The BMS estimates there is 50% SOC based on its idea that 282 is the actual full charge capacity. But that isn't a given... It's an estimation.
So it estimated wrong, and instead to correct that.... it just changes the percentage in the screen instead to actually recalculate capacity.
I'm not writing in circles. I'm trying to get you to visualize what I'm explaining.
The 50% capacity it showed, wasn't based on 50% at all. It was directly based on there being 141 miles available.
When it saw there were more miles available, instead to understand there is actually more capacity than it thought.... it just changes the percentage.
Im fairly confident I'm explaining this in a way that can be understood.
You're example of 8oz would work.... iffff our capacity wasn't always decreasing.
4 oz was 50% on day one. But 50% is no longer 4 oz at 50,000 miles. Again, this has to make sense.
The BMS estimates there is 50% SOC based on its idea that 282 is the actual full charge capacity. But that isn't a given... It's an estimation.
So it estimated wrong, and instead to correct that.... it just changes the percentage in the screen instead to actually recalculate capacity.
I'm not writing in circles. I'm trying to get you to visualize what I'm explaining.
The 50% capacity it showed, wasn't based on 50% at all. It was directly based on there being 141 miles available.
When it saw there were more miles available, instead to understand there is actually more capacity than it thought.... it just changes the percentage.
Im fairly confident I'm explaining this in a way that can be understood.
I mean it's fairly safe to say the BMS is already very conservative in its estimation because it doesn't want to leave us stranded.
So, if it sees it's been too conservative... I.E. showing 141 miles worth of energy available... when there was actually 150 miles worth of energy available.
It should adjust it's estimation to match the newly calculated capacity vs just showing an inflated SOC to match it's already miscalculated estimation.
So, if it sees it's been too conservative... I.E. showing 141 miles worth of energy available... when there was actually 150 miles worth of energy available.
It should adjust it's estimation to match the newly calculated capacity vs just showing an inflated SOC to match it's already miscalculated estimation.
E90alex
Active Member
I understand your train of thought. But the way you’re thinking about it is incorrect.
First of all, you are still hung up on the car “finding more miles”. The range is miles is calculated FROM the SOC %. Not the other way around. So it’s not that the car thinks it’s at 50% because it has 141 miles left. It showed 141 miles left because it was at 50%. Minor but important difference in cause and effect.
The total battery capacity is not changing in this scenario. Yes the total capacity can change over time due to degradation but that is not why the range/SOC is jumping.
My car SOC% has done that since brand new and would often show higher after parking at work on a hot day. The battery didn’t magically gain capacity over 100%.
So in your example of 141 miles at 50%, the BMS still thinks 100% is 282 miles when it’s showing 150 miles. Hence why it’s showing 54% now.
It does not think 100% is 300 miles now and therefore does not show 150 miles remaining as 50%.
Estimated miles = % SOC * EPA Range * Estimated degradation
The BMS is only really in charge of estimating % SOC. Actually the estimated miles is pretty meaningless because how many actual miles you get will differ wildly based on driving conditions: flat vs hills, highway vs city etc.
The BMS is only really in charge of estimating % SOC. Actually the estimated miles is pretty meaningless because how many actual miles you get will differ wildly based on driving conditions: flat vs hills, highway vs city etc.
Let's use this example in the attached pic. I just got home now. Forget about miles. Let's use capacity.
265x53/.20= 70.225 KWH of capacity.
I won't plug it in, and I'll let it sit. When I come back out in an hour... I'm confident there will be more capacity available.
Instead for the BMS to show it as additional capacity available, it will adjust the percentage to match it's calculations.
Temperature is 82°. It will not get hotter as the sun goes down. So the additional capacity it finds isn't related to temp.
I'm trying to help us all get a grasp on what is actually happening. Thanks so much for engaging!
265x53/.20= 70.225 KWH of capacity.
I won't plug it in, and I'll let it sit. When I come back out in an hour... I'm confident there will be more capacity available.
Instead for the BMS to show it as additional capacity available, it will adjust the percentage to match it's calculations.
Temperature is 82°. It will not get hotter as the sun goes down. So the additional capacity it finds isn't related to temp.
I'm trying to help us all get a grasp on what is actually happening. Thanks so much for engaging!
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That's what I would think as well. However, it's been consistently showing 2-3-4% more after settling though... even with the temperature decreasing.
I was also seeing a solid 73kwh in capacity prior to the last update. I'm having a really hard time believing I've lost 3kwh of capacity in a week with nothing changing other than the update.
I'm sure you're unicorn is still showing 82kwh though Ken!!!
I was also seeing a solid 73kwh in capacity prior to the last update. I'm having a really hard time believing I've lost 3kwh of capacity in a week with nothing changing other than the update.
I'm sure you're unicorn is still showing 82kwh though Ken!!!
ucmndd
Well-Known Member
It’s almost like estimating the energy available in a few thousand individual chemical cells based on observing their voltage is an inexact process.
Crazy.
Crazy.
E90alex
Active Member
Keep in mind these calculations are only just a ballpark estimate and you can’t take the exact number at face value. The car doesn’t show any decimals and rounding errors can cause a significant change in the results.
For example
264.5 x 52.5 / 0.204 = 68.070 kW
Or
265.4 x 53.4 / 0.195 = 72.679 kW
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