How I Recovered Half of my Battery's Lost Capacity

[Candleflame]

The BMS system is not only responsible for charging and monitoring of the battery, but computing the estimated range. The way it does this is to correlate the battery's terminal voltage (and the terminal voltage of each group of parallel cells) to the capacity. The BMS tries to constantly refine and calibrate that relationship between terminal voltage and capacity to display the remaining miles.

yes but not with 18% variability. Maybe 1% (if that)

 

[spiceagent11]

yes but not with 18% variability. Maybe 1% (if that)

Got it. Research a lot about it.

 

[phxcar12]

I've seen the service manual excerpt for the model 3 posted a few times. The BMS starts balancing at voltage above 4.0

What does that mean?

 

[Candleflame]

I find this balancing above 4.0 voltage very strange as many cars which get cycled below 4V have no trouble having the same tight balance as cars which regulary get charged to 85% (I think 85% is where most cells start to sit above 4V).

 

[WdstockWizard]

You could always try voice commands. They work well for this senior.

High tech is not for everyone but I, for one, love all the "goodies" on my Mdl S. Oh ya...I'm 78 but I don't dwell on it.

 

[awokeinthelbc]

Model 3 has this problem. My model x does not. Must be active cooling and heating elements of x that does the trick? Imagine heat pump of newer 3 and y address this misreading?

 

[Candleflame]

Model 3 has this problem. My model x does not. Must be active cooling and heating elements of x that does the trick? Imagine heat pump of newer 3 and y address this misreading?

Model 3 has by far more degradation than the Model X/S. Model X & S usually lose 5% and then maybe lose another 5% over the next few years and even old high milage cars often still only have 7-10% degradation (if that).

Model 3 degrades very quickly, with 7-10% being completely normal for a 2-3 year old car regardless of mileage.
Model 3 degradation seems also be more time based as opposed to the S/X which is more km based.

 

[CAM3RON]

I should have read this before reading the InsideEVs article that is the first to appear in a google search on this topic.

 

[scottf200]

1) No one liked the 'Scheduled Departure' idea for having more random times/durations for the OCV readings apparently.
Here is an example of someone I know and their charges that ended up below 50% over a couple of months (i.e. not consecutive days). All the rest started the SOC over 50%.
If they delayed their charging start times then they would have OCV readings 'randomly' over a couple of months.

You can automatically let it sit for X hours by just using the scheduled 'departure time'. It will calculate when to start charging based on your targeted SOC % (state of charge) and your charging speed (kW). This makes the 'sit for X hrs' automatic. And can add randomness to your array of lower SOC values if your miles uses all week and weekend changes.

I keep suggestion to folks to just do a scheduled departure time charge then the car will randomly start at different times (letting it have more idle time) to finish by say 6am at 80% SOC or whatever.

Re: If they delayed their charging start times then they would have OCV readings 'randomly' over a couple of months.

Tesla is now recommending to use 'scheduled departure' as I suggested back in April.

Bullet point 1 below -- recommendation from the OP
Bullet point 2 below -- use 'scheduled departure' to let car sit for OCV settled reasons.

 

[AlanSubie4Life]

Re: If they delayed their charging start times then they would have OCV readings 'randomly' over a couple of months.

Tesla is now recommending to use 'scheduled departure' as I suggested back in April.

Bullet point 1 below -- recommendation from the OP
Bullet point 2 below -- use 'scheduled departure' to let car sit for OCV settled reasons.

"Also we have found customers that switch their 'Energy Display' from distance to energy have reported a better experience as again the Distance displayed is only an estimate."

Lol.

 

[HelixSpiral]

^ Haha I LOLed at that too.

 

[Candleflame]

i mean.... i guess it is an estimate based on a highly accurate BMS reading +-3 or 4 km.

 

[beenmb]

Wow thank you so much SomeJoe7777 and other members for sharing this super helpful information. Have been loving my M3P for three years.
So glad I don't own a Chevy Bolt.

 

[scottf200]

A Facebook post supposedly from Tesla ... but it matches the main trains of thought in the thread AFAIK.

 

[Candleflame]

A Facebook post supposedly from Tesla ... but it matches the main trains of thought in the thread AFAIK.

this is not teslas writing style.

 

[Zoomit]

A Facebook post supposedly from Tesla ... but it matches the main trains of thought in the thread AFAIK.

Please provide a link to the actual FB post.

 

[scottf200]

this is not teslas writing style.

Please provide a link to the actual FB post.

Sorry, it was just in a thread that started out from a new owner that asked what is the best way to charge my car for longevity type of question. Then there was dozens of back and forth opinions. If I stumble across it I will update. It seems like a good summary that you could give new Tesla owners and not point them to this long thread!

It matched the OPs ideas of leaving the car at diff/lower SOC: "So, when does the BMS take OCV readings? ..."

Probably something like a Tesla owner got back from some person at tesla with their generalize response ... like the screen shot I posted here:

How I Recovered Half of my Battery's Lost Capacity

The BMS system is not only responsible for charging and monitoring of the battery, but computing the estimated range. The way it does this is to correlate the battery's terminal voltage (and the terminal voltage of each group of parallel cells) to the capacity. The BMS tries to constantly refine...

teslamotorsclub.com

 

[KenC]

A Facebook post supposedly from Tesla ... but it matches the main trains of thought in the thread AFAIK.

I doubt that's from "Tesla", but it could be from an employee at a Service Center. Of course, we've seen lots of those comments, and they're all over the place.

In regards to the actual advice, I don't do the first 3. the 4th and 5th are not applicable to me.

 

[Martimus]

Thank you for this. Very helpful!

So, knowing all of this, here's what I did:

1. I made it a habit to make sure that the BMS got to take OCV readings whenever possible. I turned off Sentry mode at work so that OCV readings could be taken there. I made sure that TeslaFi was set to allow the car to sleep, because if it isn't asleep, OCV readings can't get taken.

2. I quit charging every day. Round-trip to work and back for me is about 20% of the battery's capacity, and I used to normally charge to 90%. I changed my standard charge to 80%, and then I began charging the car at night only every 3 days. So day 1 gets OCV readings at 80% (after the charge is complete), day 2 at about 60% (after 1 work trip), and day 3 at about 40% (2 work trips). I arrive back home from work with about 20% charge on that last day, and if the next day isn't Saturday, then I charge. If the next day is Saturday (I normally don't go anywhere far on Saturday), then I delay the charge for a 4th day, allowing the BMS to get OCV readings at 20%. So now my BMS is getting data from various states of charge throughout the range of the battery.

3. I periodically (once a month or so) charge to 95%, then let the car sleep for 6 hours, getting OCV readings at 95%. Don't do this at 100%, as it's not good for the battery to sit with 100% charge.

4. If I'm going to take a long drive i.e. road trip, then I charge to 100% to balance the battery, then drive. I also try to time it so that I get back home with around 10% charge, and if I can do that, then I don't charge at that time. Instead, let the car sleep 6 hours so it gets OCV readings at 10%.

These steps allowed the BMS to get many OCV readings that span the entire state of charge of the battery. This gets it good data to run an accurate calibration computation.

So what's the results?

On 1/20/2020 at 30,700 miles, I was down to 270 miles full range, which is 40.8 miles lost (15.1 %). The first good, accurate recalibration occurred 4/16/2020 at 35,600 miles and brought the full range up to 286 miles. Then another one occurred on 8/23/2020 at 41,400 miles and brought the range up to 290 miles, now only a 20 mile loss (6.9 %).

Note that to get just two accurate calibration computations by the BMS took 7 months and 11,000 miles.

So, to summarize:

1. This issue is primarily an indication/estimation problem, not real battery capacity loss.
2. Constant Sentry mode use contributes to this problem, because the car never sleeps, so no OCV readings get taken.
3. Long voltage stabilization times in the Model 3 prevent OCV readings from getting taken frequently, contributing to BMS estimation drift.
4. Constantly charging every day means that those OCV readings that do get taken are always at the same charge level, which makes the BMS calibration inaccurate.
5. Multiple accurate calibration cycles may need to happen before the BMS accuracy improves.
6. It takes a long time (a lot of OCV readings) to cause the BMS to run a calibration computation, and therefore the procedure can take months.

I would love if someone else can perform this procedure and confirm that it works for you, especially if your Model 3 is one that has a lot of apparent degradation. It will take months, but I think we can prove that this procedure will work.

Thank you for this, very helpful!

 

[AAKEE]

I find this balancing above 4.0 voltage very strange as many cars which get cycled below 4V have no trouble having the same tight balance as cars which regulary get charged to 85% (I think 85% is where most cells start to sit above 4V).

I did progressively increase the SOC, and kept an eye on the cell imbalance. 60-70-80-90. There was no balancing until 90%. The imbalance stayed the same each time a few hours after reaching the SOC, except when reaching 90%, then the imbalance decreased quite quick to 2mV. (Was higher before).
Id say that is a clear indiocation that balancing doesnt occur below (about) 90%.

[Edit]Post about the balancing: MASTER THREAD: 2021 Model 3 - Charge data, battery discussion etc