What determines the charging curve? The car or the charger?

[Buffalo Bob]

Say I plug in at a public charging station at a fairly low SOC, and I set a reasonable daily limit. Now, assume I'm the only car there, it's a temperate day, I'm fully preconditioned, the station is not being throttled down, and the electrical supply to the station remains constant. My charging rate initially runs up to XXX kWh, and of course I watch that number steadily decline over time as the SOC goes up. I understand that the initial rate itself could be higher or lower depending on the specs of the car, but once that initial rate is established, is the rate of decline determined by the car's software, the station's software or some combination of both? (Remember I'm assuming that no other factors change at the station, such as a brown out or another car pulling up to charge next to me.) Whatever the source, is the rate of decline determined based simply on elapsed time, the SOC, the battery temperature (if it's the car setting the curve), or some other specific performance monitoring? So many questions! Thanks!

 

[Steveinarizona]

Great questions. While my usage does not make me use these chargers (as of yet), I am curious as to the answers.

 

[DeaneG]

The car controls the charging current at all times, possibly limited by the station's capability.

The car's BMS monitors the current condition and design limitations of the battery and adjusts charging current for safe operation during the course of the charge.

The station may limit charging current to a lower value than the car asks for, but this station limit is usually a fixed value unless the station's charging connector gets too hot during charging.

 

[Buffalo Bob]

Thanks. For my purposes, let's leave changes at the charger, such as hot cables, out of the equation. Is Lucid is gathering data on how the car is charging? If so, I would think that they would be adjusting the performance curve specs via OTA from time to time. Has that happened?

 

[DeaneG]

Thanks. For my purposes, let's leave changes at the charger, such as hot cables, out of the equation. Is Lucid is gathering data on how the car is charging? If so, I would think that they would be adjusting the performance curve specs via OTA from time to time. Has that happened?

To my knowledge the charging curve hasn't changed since the cars were shipped. The curve is determined mainly by battery chemistry and the engineering/marketing trade-off of battery thermal management design (cost and volume in the car) and battery longevity vs charging speed bragging rights.

 

[Buffalo Bob]

To my knowledge the charging curve hasn't changed since the cars were shipped. The curve is determined mainly by battery chemistry and the engineering/marketing trade-off of battery thermal management design (cost and volume in the car) and battery longevity vs charging speed bragging rights

Very interesting. I figured it had to be the car, but the variability in the drop-off rate seemed to be inconsistent in fairly similar situations, and I often charge very early when I'm the only car there, and under fairly consistent weather conditions. Perhaps it's more just perception on my part. Thanks, @DeaneG!

 

[scal_air]

DeaneG gives an excellent answer but my short reply is both. In my case I rarely reach the car's potential charging speed because the EA's around me are almost always busy and the speed is throttled by the station. And as you well know, there is a curve depending on SOC. I have learned to practice patience - Thanks EA!

 

[Buffalo Bob]

DeaneG gives an excellent answer but my short reply is both. In my case I rarely reach the car's potential charging speed because the EA's around me are almost always busy and the speed is throttled by the station. And as you well know, there is a curve depending on SOC. I have learned to practice patience - Thanks EA!

You're absolutely right about there being many factors like throttling and other cars affecting the EA side of the equation, and also non-EA things like the outside temperature. I was deliberately trying to factor out all those exogenous factors, in order to better understand how the process works independent of those variables.

I think the biggest mistake I make when only considering the Lucid side of the charging curve is that I tend to charge to an 80% SOC when I am around a 40% SOC, and I could just as easily wait until I'm at around 20%. I'll wager the curve would look much better from that starting point.

 

[coma24]

I'll wager the curve would look much better from that starting point.

The curve has been reasonably well-documented, numerically and graphically. You will, without question, be able to charge at a faster rate in the window from 20% to 40% SOC as compared to, say the 60-80% portion, here's one such thread if you haven't seen it already: https://lucidowners.com/threads/charging-curve-logs-post-2-1-52.8093/

The specific numbers will vary between models, presumably, however, the trend in undeniable, once you're above 10%, there is a inverse relationship between the SOC and the rate requested by the car.

 

[Steveinarizona]

I think the biggest mistake I make when only considering the Lucid side of the charging curve is that I tend to charge to an 80% SOC when I am around a 40% SOC, and I could just as easily wait until I'm at around 20%. I'll wager the curve would look much better from that starting point.

Looking at the charge curve it would also probably make sense to charge to 70% instead unless you really needed the extra 10%:

Watch World's First Lucid Air 0-100% DC Fast Charge Test

The very first DC fast charge recording of the Lucid Air. We find out how fast does the Lucid Air charge in our Lucid Air EV charging review.

insideevs.com

 

[Rogue]

The curve has been reasonably well-documented, numerically and graphically. You will, without question, be able to charge at a faster rate in the window from 20% to 40% SOC as compared to, say the 60-80% portion, here's one such thread if you haven't seen it already: https://lucidowners.com/threads/charging-curve-logs-post-2-1-52.8093/

The specific numbers will vary between models, presumably, however, the trend in undeniable, once you're above 10%, there is a inverse relationship between the SOC and the rate requested by the car.

This thread is THE thread with charging curves for most trims and/or equivalent trims via graphs and lists. There is a new thread awaiting data on the 24' GT models.

 

[SM_NCarolina]

The answer to your question has two parts, one the basic science and other how our engineers try to optimize battery performance. Most of the answers above address the second aspect.

The first part is basic science constraint that you might have observed for many years in rechargeable AA batteries, phone charging and other rechargeable devices. This limitation comes from the batteries themselves, as the batteries charge the rate of charge decreases proportionally to the SOC. The phenomenon observed in rechargeable batteries, where the charging rate decreases as the state of charge (SOC) increases, is a well-established principle in battery science. This behavior is attributed to the intrinsic properties of the battery itself. During charging, as the SOC rises, the battery progressively presents a higher impedance to the current flow, resulting in a gradual decrease in the charging rate.
"