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2019 Bolt built June 10th. 66kWh battery?
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Discussion Starter #41
I have been meaning to post about the accuracy of using TorquePro to examine KWh used. I learned from the incomparable Sean Graham, the person mainly responsible for getting the Bolt to work with TorquePro, that kWh measurements in TorquePro are not very reliable.
KWh equals amps times volts. Because of the peculiar way that TorquePro reports data, kWh is calculated from a voltage measurement and an amperage measurement that are not simultaneous. In other words, the kWh value recorded in TorquePro could be an amperage from an event when you used a lot of juice to climb a hill times a voltage from an event that happened a second or two later when you were coasting downhill.
However, by recording data every half second, the form of the curves I presented in an earlier post are still good. The representation of how battery capacity changes over the range of SoC (from 100% charged to 15% or 20%), is sound, even though individual values for kWh may not be very accurate.
 

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Discussion Starter #43
kW equals amps times volts. But yes, if it is sampling these at different times the kW will be off, so the kWh will be also.
Picky, picky- but yes, I should be more precise. Someday I'll get it right the first time...

For those who may be curious about what GJetson means and why it matters...
Yes, kW is an instantaneous value, and the values for volts and amps used by TorquePro to calculate kW are also instantaneous. However, a kWh, the unit used to describe battery capacity, is how many kWs are available over a time period of one hour.

TorquePro records instantaneous values for amps and volts every half-second (the settings can be changed); unfortunately those values for volts and amps are not recorded at the identical half-second. TorquePro multiples those discordant volt and amp values to get instantaneous kW. However, some pairs of volt/amp values could have been recorded as much as 6 seconds apart. An amp times a volt six seconds later is not very meaningful if the power applied changes during those 6 seconds, for example, due to acceleration up a hill, regen braking, or a gust of wind.

I found it interesting that I always received a pretty substantial underestimate of kWh used in TorquePro- on the order of a couple-a-few kWh less compared to what the info screen told me at the end of a long trip. This is almost certainly because during deceleration not as many kWhs are regenerated as the amount of kWhs used during rapid acceleration. It's tough to see more than about 13 or 14 kW on the DIC while regen braking for very long. It is not so tough to see 30 or 60 or more kW over a few seconds or longer when accelerating and/or climbing a steep hill. When driving steadily, there is no bias. Therefore, the largest magnitude of bias occurs when accelerating. Before and during acceleration TorquePro ends up multiplying a large amp, for example, used when accelerating by a too small volt used a few seconds before speeding up. That small volt times the large amp produces an underestimate for kW for the instant that the amp was used. Therefore, the largest bias is that a large amp, say, should have been multiplied by a bigger volt (or vice-versa), leading to an accumulating underestimate of actual kWh used.

To obtain the kWh values on the State of Charge vs. kWh curves of an earlier post, I divided instantaneous kW calculated by TorquePro by 7200 (because there are 7200 half-seconds in one hour) and calculated a running total. Although the exact numbers for kWh used are an underestimate, the arched shape of the curve is almost surely the correct form of the relationship between state of charge and kWh used.

Comparatively, when you're charged-up and use a kWh, it looks like you could go forever. When you use a kWh when low on charge it looks like you'll run out of power yesterday! Therefore, the best estimates of overall capacity are made by subtracting kWh values at intermediate states of charge. The capacity value is more representative when state of charge is between 75% and 25%, or 80% and 30%, than when SoC is between 100%-50%, for example.
 

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I think the only way to know for sure is to do a discharge test. Any on the fly calculations are going to be off.

I ended my test at 23%. Long way to go, but I had a long drive coming up and needed some extra juice. At that point I was calculating right around 60 kWh, +/- 1 kWh.

I am now convinced that the Bolt makes inaccurate calculations that give false impressions of range and battery capacity at some SOCs. This is not any criticism of the Bolt as a whole. Battery discharge is not linear in terms of voltage, so car needs to calculate percentage and range in a round-about way and periodic errors are understandable.

The same goes for Torque Pro however. The calculation can only be based off of data the Bolt reports, so errors will occur. Depending on how the Bolt tracks and reports data, this could get worse over time without a full charge.

Tie in with "balancing" which is probably more to do with the car calibrating when fully charged and you get a picture of why some Tesla owners had issues with their cars losing range quickly when kept at mid charge for long periods of driving, or why some forum members here have reported strange behaviour when not charged to full on occasion. Some of this is speculation, but based off my knowledge of batteries and electronics it could be an explanation.

Lastly, I can't help myself:
1 kW = 1000W
1 W = 1 V * 1 A
Volts * Amps are not equal to a kW.
Only putting this here because I have seen the formula given repeatedly on this forum as kW = V * A which could be confusing to some.
 

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I am now convinced that the Bolt makes inaccurate calculations that give false impressions of range and battery capacity at some SOCs. This is not any criticism of the Bolt as a whole. Battery discharge is not linear in terms of voltage, so car needs to calculate percentage and range in a round-about way and periodic errors are understandable.
The main culprit for the false impressions of range at certain SOC level is caused by the fact that the displayed SOC does not decrease in a straight line compared with raw SOC.

30343

This graph shows the displayed vs. raw SOC data that I recorded off the OBD-II port of my Bolt EV for more than two years. If look at the slope in 25% steps, you’ll see that the region between 25 and 75% has more or less "normal". Past 75%, the slope gets less steep. Conversely, the slope gets steeper if you have 25% or less.
 

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2019 Bolt built June 10th. 66kWh battery?
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Discussion Starter #47
The main culprit for the false impressions of range at certain SOC level is caused by the fact that the displayed SOC does not decrease in a straight line compared with raw SOC.

View attachment 30343
This graph shows the displayed vs. raw SOC data that I recorded off the OBD-II port of my Bolt EV for more than two years. If look at the slope in 25% steps, you’ll see that the region between 25 and 75% has more or less "normal". Past 75%, the slope gets less steep. Conversely, the slope gets steeper if you have 25% or less.
If only we knew what exactly "Raw SoC %" really is!
 

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If only we knew what exactly "Raw SoC %" really is!
Raw SoC value is what the BMS considers the actual (true) charge of the battery is. And based on my observations and many others, the PID #015B from the OBD-II port, which is generally referred to as "Hybrid battery pack remaining life", is indeed the raw SoC value for Bolt's propulsion battery.

I should note that GOM's range estimate is calculated with the displayed SoC value. Because of this, it feels like you get worse mileage (i.e. have the battery deplete faster) when you have less battery remaining. The raw SoC follows the kWh consumption relatively linearly, though.
 

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Generally speaking, it's true that the GOM shouldn't be used to calculate capacity. That said, in my example (details below), it seems there's no way I would have been able to drive even the minimum 27 miles shown if my pack was 60 kWh (and many claim we only have 57 kWh useable). At most, I'd get another 12 miles or so and maybe as little as 3 miles. That's a significant difference from the 34 miles the display was showing me. I concede that it's an estimate but that strikes me as dangerously inaccurate if you're on a long road trip.

"I drove 185.8 miles (starting at 100%) using 56.2 kWh. The display said I had 34 miles left (minimum 27) with the trip average being 3.3 mi/kWh. The battery level was at 15% - which could in theory be as low as 11% because of how it's displayed"
 

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Discussion Starter #51
To estimate capacity, the soundest method would be to use the division of kWh by one minus percent remaining. Doing that with the numbers you provided gives values between 62.4 - 66.1 kWh for the range of 10-15% remaining. Therefore, it seems possible that you have the larger pack. Keep measuring and notice also driving conditions. Among other factors, conditions closer to steady driving at moderate speed with constant temperatures near 75 degrees F will be kindest to battery capacity.
The range indicator could easily produce a rosy overestimate if you had been driving slowly downhill and/or regen braking a lot for example, over your last miles compared to your trip average.
 

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Keep in mind, Peukert's Law doesn't apply to lithium batteries, and in fact, the internal resistance of lithium batteries decreases as they get hotter. Higher loads under hotter temperatures should actually report higher capacity, while lower loads at colder temperatures should report lower capacity. That's likely what causes the ~1 kWh capacity difference that encounter from session to session.
 

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This is the problem with the GOM. The reported range can vary dramatically based on recent driving conditions. In my opinion it can't be used to calculate battery capacity. The best bet would be known kWh used, with remaining reported percentage in the app. The lower the SOC the better, as there are 600 Wh per percentage point. I know that using the reported range for me as a factor in the calculation gives bad and wildly varying results even when the efficiency appears to be constant.

I recommend more people try a 100% charge and discharge as far as comfortable to see where they end up.
 

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Discussion Starter #54
Keep in mind, Peukert's Law doesn't apply to lithium batteries, and in fact, the internal resistance of lithium batteries decreases as they get hotter. Higher loads under hotter temperatures should actually report higher capacity, while lower loads at colder temperatures should report lower capacity. That's likely what causes the ~1 kWh capacity difference that encounter from session to session.
Thanks, I am still learning. I knew that Li-ion batteries degraded more quickly at higher temperatures, but I did not realize that they actually gained (apparent) capacity. Of course that capacity gain is not permanent! I did learn, because of your comment, that the capacity will increase at higher temperatures- up to ~115 degrees F, but that cycling (discharging and charging) at these higher temperatures more rapidly decreases capacity over time (see the figure below). So, to carry the conversation a step further, it seems like yes and no? Yes: a higher capacity reported at a higher temperature, all else being equal, but overall no: more rapid degradation of capacity with repeated discharge/charge at higher temperatures.

It is also interesting to me because I am comparing the capacity estimates I calculate at the very moderate summer temperatures of Alaska near the coast- the record high temperature for my town is 81 degrees F- to folks presumably calculating their capacities in warmer climates. Since the main point of this thread is really to figure out whether or not other pre-2020 Bolt owners also received 66 kWh batteries, that tidbit of temperature/capacity comparison further makes me think that I really must have a 66 kWh pack in my 2019 car. Using Raw SoC % over the range from 100% to 10-15%, I'll get estimates over 68.5 kWh. Using a more limited portion of the SoC range, between 80 and 30%, I can get over 70 kWh. I'll collect data for two more 230+ mile trips early next week.

This has real consequences, because if I ever sell the car, it would be nice to prove to a prospective buyer that it has the bigger battery of later model years. Especially the increased range that should go along with the larger battery, which is what most buyers would probably focus on.

This plot for a Sony Prismatic LCO battery may or may not directly relate to the LiMM CF chemistry of the Bolt battery:
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from: Ma et al. 2018. Temperature effects and thermal impact on Li-ion batteries: a review. Progress in Natural Science: Materials International. https://doi.org/10.1016/j.pnsc.2018.11.002/pii/S1002007118307536#f0025 (open source)

It would be more interesting if the authors showed the capacity at 25 degrees of the batteries that were cycled at 35 or 45 degrees.
 

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Discussion Starter #55
This is the problem with the GOM. The reported range can vary dramatically based on recent driving conditions. In my opinion it can't be used to calculate battery capacity. The best bet would be known kWh used, with remaining reported percentage in the app. The lower the SOC the better, as there are 600 Wh per percentage point. I know that using the reported range for me as a factor in the calculation gives bad and wildly varying results even when the efficiency appears to be constant.

I recommend more people try a 100% charge and discharge as far as comfortable to see where they end up.
Yeah, I agree that the gold standard is really a full discharge. However, let's also test the accuracy of comparing the capacity calculated from those full discharge cycles with estimates of capacity from kWh used between 80% and 25% charge, since they are so much easier to obtain.
 

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Yeah, I agree that the gold standard is really a full discharge. However, let's also test the accuracy of comparing the capacity calculated from those full discharge cycles with estimates of capacity from kWh used between 80% and 25% charge, since they are so much easier to obtain.
Yeah that is worthwhile as well. I haven't tested that specifically, but I know that 60% and above works out to 65 or 66 kWh repeatedly, very high capacity is unusable due to that initial undetected 3% loss, 50% worked out to around 60-61, 45 down to around 30% was showing higher again: around 62kWh.

The problem with starting below 100% is that you need to make some assumptions about what happened in that first 20%
 

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Discussion Starter #57
Yeah, I agree that the gold standard is really a full discharge. However, let's also test the accuracy of comparing the capacity calculated from those full discharge cycles with estimates of capacity from kWh used between 80% and 25% charge, since they are so much easier to obtain.
Yeah- probably best if only charging to 75-80%. Easier that way too- you only need to look at one value- kWh used at 50, 30 or 25%
 

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Discussion Starter #58
Yeah- probably best if only charging to 75-80%. Easier that way too- you only need to look at one value- kWh used at 50, 30 or 25%
However, I realize that with Hilltop Reserve pre-2019 that's not so easy- in 2019 and beyond drivers can set the "Target Charge Level" in 5% increments. This thread needs to explore theory and methods of estimating capacity, but it is really about who as a 66 kWh pack prior to 2020?
 

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Keep in mind, Peukert's Law doesn't apply to lithium batteries, and in fact, the internal resistance of lithium batteries decreases as they get hotter. Higher loads under hotter temperatures should actually report higher capacity, while lower loads at colder temperatures should report lower capacity. That's likely what causes the ~1 kWh capacity difference that encounter from session to session.
Is that why I get crazy mileage right after completing a charge? The other day I ran an errand right after charging. It was a round trip of 7.4 miles. Energy used was 0.2 kWh. That's 37 mi/kWh. This morning I did a 4 mile round trip to drop off the kid. Energy used: 0 kWh. I guess I could have driven forever! I only see these kinds of numbers coming right off a charge.
 

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Is that why I get crazy mileage right after completing a charge? The other day I ran an errand right after charging. It was a round trip of 7.4 miles. Energy used was 0.2 kWh. That's 37 mi/kWh. This morning I did a 4 mile round trip to drop off the kid. Energy used: 0 kWh. I guess I could have driven forever! I only see these kinds of numbers coming right off a charge.
I suppose that could also indicate some sort of hidden upper buffer/capacity. Basically, you could have an additional .5 to 1 kWh of available energy at the top of the charge that the BMS isn't reporting/accounting for.
 
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