Charging Beyond the Charge Limit

[hmp10]

On a recent road trip we had two episodes when the charging limit was set to 80% but the car charged beyond that limit. The first time was at a ChargePoint Level 2 charger at a hotel, when the car charged up to 85%. The second time was when we got home and plugged into our home plug, when the car charged to 83%.

Both the Atlanta Service Center (which we called about the first incident) and Lucid Customer Service told us they have never seen this problem. Has anyone on the forum seen this issue?

 

[Tâm]

I've owned an 3 different EVs since 2012 prior to the current Lucid so I do see this happen in the previous brand and I wouldn't be surprised to see the same in Lucid.

I assumption is the BMS Battery Management System at work.

It calibrates and recalibrates to reflect the most accurate State of Charge.

It could stop charging at 80% and recalibrate that oops, the new calibration no longer says 80 but actually 83%.

 

[hmp10]

I've owned an 3 different EVs since 2012 prior to the current Lucid so I do see this happen in the previous brand and I wouldn't be surprised to see the same in Lucid.

I assumption is the BMS Battery Management System at work.

It calibrates and recalibrates to reflect the most accurate State of Charge.

It could stop charging at 80% and recalibrate that oops, the new calibration no longer says 80 but actually 83%.

In an incident last Sunday the car went 5% over the charge limit.

I have owned two Lucids over the past two and a half years. Neither ever did this before this week.

Lucid Customer Service have never heard of it happening. A mobile tech in Charlotte and a Service Center Manager in Atlanta have never heard of it happening.

I do not believe this is simply the BMS doing its job, nor does anyone to whom I've talked at Lucid. They are taking the car in next week for examination.

 

[hmp10]

I've owned an 3 different EVs since 2012 prior to the current Lucid so I do see this happen in the previous brand and I wouldn't be surprised to see the same in Lucid.

I assumption is the BMS Battery Management System at work.

It calibrates and recalibrates to reflect the most accurate State of Charge.

It could stop charging at 80% and recalibrate that oops, the new calibration no longer says 80 but actually 83%.

Seems you were right. This is the report I got back from the Miami Service Center:

"Battery management system recalculates State of Charge constantly as cells balance and voltage moderates. Sometimes it will recalculate a few percentage points higher/lower and sometimes it will be on what you set it to. This means the Battery Management System is doing it's job."

However, I still don't understand why I had never seen this in over two and a half years of driving a Lucid and then suddenly had it happen twice in one week.

 

[DeaneG]

Seems that something in the battery assembly is acting in a way that the BMS software didn't anticipate.

 

[hmp10]

Seems that something in the battery assembly is acting in a way that the BMS software didn't anticipate.

Our HV battery pack, Wunderbox, and rear drive unit were replaced several months ago. I'm wondering if that had anything to do with this, although it only happened a week ago.

 

[Tâm]

However, I still don't understand why I had never seen this in over two and a half years of driving a Lucid and then suddenly had it happen twice in one week.

Some factors could be: It's a guessing formula so it may take some time to correct the drift in battery gauge accuracy. Firmware updates might have made the calculations more robust...

 

[Tâm]

Our HV battery pack, Wunderbox, and rear drive unit were replaced several months ago. I'm wondering if that had anything to do with this, although it only happened a week ago.

Could be because all those components affect the state of charge. Each has its own individual variations even when they are within the specs.

 

[terrycs]

I've never seen my car go over during L1 charging at home. I've never left my car plugged in overnight using L2. I can see it overshooting a little since the car is recalculating SOC and trickle charges as long as cable is connected.

 

[Adnillien]

Keep in mind how the SOC estimated. If a battery pack is resting without charging or discharging for a few hours the SOC can be determined from the cell voltage and temperture. When driving or charging this method does not work so most BMS systems also count Coulombs or electrons. Counting Coulombs is not 100% accurate and the errors accumulate over time. Hence, the SOC estimate becomes less accurate the longer that you drive. After a day of driving, charging, driving and then overnight charging the errors are at their highest. When level 2 charging stops, the battery rests and then the BMS system can accurately determine SOC from cell voltage/temperature so it re-calibrates.

I not not seen errors as high as @hmp10 reports though but some error is understandable.

 

[hmp10]

Keep in mind how the SOC estimated. If a battery pack is resting without charging or discharging for a few hours the SOC can be determined from the cell voltage and temperture. When driving or charging this method does not work so most BMS systems also count Coulombs or electrons. Counting Coulombs is not 100% accurate and the errors accumulate over time. Hence, the SOC estimate becomes less accurate the longer that you drive. After a day of driving, charging, driving and then overnight charging the errors are at their highest. When level 2 charging stops, the battery rests and then the BMS system can accurately determine SOC from cell voltage/temperature so it re-calibrates.

I not not seen errors as high as @hmp10 reports though but some error is understandable.

The car fairly often shows 79% charge after overnight charging with the limit set to 80%, and I thought little of it. But I had never seen it go over. I'm a real stickler about not letting the battery sit at high charge for long periods, and the 85% reading of the first incident really alarmed me. I was already doing DCFC up to 95% on this trip because of the charging issues we were having and wanting to leave enough margin if we arrived at a station and had to look for an alternative, and I didn't want to push my luck.

 

[Adnillien]

The car fairly often shows 79% charge after overnight charging with the limit set to 80%, and I thought little of it. But I had never seen it go over. I'm a real stickler about not letting the battery sit at high charge for long periods, and the 85% reading of the first incident really alarmed me. I was already doing DCFC up to 95% on this trip because of the charging issues we were having and wanting to leave enough margin if we arrived at a station and had to look for an alternative, and I didn't want to push my luck.

While I understand why there are errors in the estimated SOC, a 5% error is much more than I would expect. Tom Moloughney reported a fairly large error when he drove his F150 Lightning from new Jersey to Florida but that was a lot longer drive with no overnight stops. I hope that customer care forwarded your concern to the battery team because Lucid may need to do some tweaking on the BMS software to reduce the error.

 

[EVCar]

My limit is set at 80%.
In the last 2 months, I have noticed that within 1-2 hours, the SOC would go down to 79% and remain there until I drive the car.
Is this normal?

 

[Worldwide Beagle]

My limit is set at 80%.
In the last 2 months, I have noticed that within 1-2 hours, the SOC would go down to 79% and remain there until I drive the car.
Is this normal?

Very normal. Someone on the forum explained months ago and it's a hoot. Your car stops charging at 80.0000% SOC. With any tiny tiny power use, the SOC on your car goes down to 79.9999%. And, your app and dash will then read 79%. No rounding up....

 

[EVCar]

Very normal. Someone on the forum explained months ago and it's a hoot. Your car stops charging at 80.0000% SOC. With any tiny tiny power use, the SOC on your car goes down to 79.9999%. And, your app and dash will then read 79%. No rounding up....

Ok, I won't lose any sleep over this then. Thanks.

 

[borski]

Very normal. Someone on the forum explained months ago and it's a hoot. Your car stops charging at 80.0000% SOC. With any tiny tiny power use, the SOC on your car goes down to 79.9999%. And, your app and dash will then read 79%. No rounding up....

It truncates, but I actually prefer that. I’d rather be on the safe side, since it’s an estimate anyway, than overconfident.

 

[EVCar]

It truncates, but I actually prefer that. I’d rather be on the safe side, since it’s an estimate anyway, than overconfident.

Just curious when to truncate vs. round up or down according to convention.
I don’t remember learning about truncating when I took physics in the same class room with Sir Newton