[thayden44]

The procedure that you’ll find many other places online for recalibrating your BMS mileage estimate requires you to bring the battery to a very low state of charge and then charge it to a very high state of charge so the BMS “sees” the full range of voltages throughout the entire state of charge of the battery.

This is commonly stated for many things that use Lion batteries, including cell phones. I wonder if it matters here for Tesla, or are they at such a higher plane of technology that this isn't necessary.

 

[aadams1278]

This is commonly stated for many things that use Lion batteries, including cell phones. I wonder if it matters here for Tesla, or are they at such a higher plane of technology that this isn't necessary.

Anecdotal evidence seems to support it making improvements. I’ve seen some notable improvement myself as well after 75,000 miles.

 

[GadgetX]

I am not an electrical engineer but I have an observation that baffled me. So I have a 2020 MSP. I have FUSC so I charge the car at a 20 mile away SC. Last time I charged to 90% from 4% (much lower than usual). After charging then I toggled the battery from % to miles it said I had 304 miles. We were going to visit my wife's sister the next day which uses approx 250 miles round trip. So when I got home the previous night I topped off with the Tesla V3 Wall connector. stopped at 90%. The next morning when I toggled from % to miles it said 321 miles. That is real close to what I was getting when the car was new at 90%.

Well here is my question from that observation. Could the cell BMS be triggered on low SOC or a combination of low and high SOC. One for the experts.

Just a data point.

M

 

[garsh]

Could the cell BMS be triggered on low SOC or a combination of low and high SOC.

The BMS can estimate the battery state better when it sees a larger range of charge states. This is orthogonal to the BMS balancing cells.

 

[Rub"Y"]

For others who were wondering about state of charge being higher than the preset value. Mine often has 2-3% higher state when I check it in the morning. Last night couldn't sleep so I checked after my RubY finished charging at 3:40 am, it stated 406Kms at 79%, I had set it to charge for 80%

Just now I checked. 407Km @ 80%

BMS doing it's thing, didn't change much but sometimes I've seen it stop @80% and by the time I get in it around 8 or nine it will read 83% I believe all of this to be normal. It seems to happen less when I charge at 32 amps than when I was charging at 21 amps. Probably battery temperature related. Maybe better managed at 32 amps. Dunno!

 

[Rub"Y"]

Again this morning, Charging stopped @ 1:20 am after a scheduled "start charging" @ 00:00. Was listing 80% - 407Kms, later this morning @ 6:39 it's showing 81% - 415Kms. So has to be normal. Last post on this subject promise!

 

[zroger73]

I, too, have noticed unexpected changes to displayed SOC a few times over ~6 months and ~7,900 miles. However, they usually occur almost immediately after charging or a drive. The first time I noticed it a few months ago, the SOC jumped to 73% almost immediately after charging stopped at 70%. I've also had it happen the other direction. Just a few weeks ago, I charged to 70%. Immediately after I disconnected the charging handle, the SOC fell to 68%. I've also seen the SOC change 2-3% in both directions just seconds or minutes after a drive.

I generally keep the SOC within a narrow range around 50%. I plan to keep doing what I've been doing because I've noticed no significant degradation. When the vehicle was new, a 70% SOC = 230 miles. Now, a 70% SOC = 229 miles. The only time the vehicle was charged above 80% was the day I took delivery when it was charged to 100%.

 

[Rub"Y"]

Stopped charging at 2:20 from midnight. SOC displayed was 80% set at 80%. This morning at 8:00 displaying 83%. 420Kms, 261 mi

 

[jim0266]

In the Model 3 and Y there are 96 series sets of 46 cells in parallel. So the loss of one cell in the 46 would reduce capacity in that set by 1/46 or about 2.2%. But because that set of 46 is in series with 95 other sets of 46, the whole pack possibly has reduced capacity depending on how the BMS works. If it can compensate for that cell loss then the pack loss is only about 0.023%.
The total number of cells in the pack is 46 X 96 = 4,416
There is a dongle you can buy so you can hook up a Bluetooth adaptor and read the CAN bus messages then use the 'Scan My Tesla' app to view battery voltages. Here is a screenshot from my 2018 Model 3 Performance. It is normally charged to 80% and has about 35,000 miles on it. You can see the high and low cell voltage differs by 4.012 - 4.006 = 0.006 Volts. I would not expect much more range from further balancing.

Thanks for this post @Feathermerchant. Interesting and helpful. If you can confirm a few things, 80% SOC might be good enough to keep the battery pack in decent BMS balance.

A few questions for you:

• How often do you charge beyond 90%?
• Do you let the car sleep for 4-6 hrs often at various SOC levels (especially if you charge to 90 or beyond)?
• Do you let the car sample various SOC levels?
• What's your low end SOC you try to hit for sampling?

I ask because my 2019 LR Model 3 is not too far behind yours at 28K miles. Reference SMT screenshots are attached. First one is the current car readings. Then 2nd is when I hit 6mV difference recently after a low SOC sleep. I'd say we have similar nominal full pack readings considering your car is a year older with 7k more miles.

6.00mV seems adequate to me as well if you are only charging to 80%. I'm more conservative than you. I've still never charged to 100% and only charged to 90% a few times. Each time I've gone to 90% I've Iet the car deep sleep 4-6 hours. The last time I charged "high" was to 91% was on Dec 25, 2022. My car sits between drives from 30-50%, usually on the lower end. Most of the charging cycles are between 70-30%, even on long road trips. Sometimes I'll shoot for a 15% SOC level when arriving home to sample the low end.

No doubt a few higher charges would bring down my cell imbalance, which is usually around 14mV these days, but I've seen it as low as 6mV recently when I let the car sleep at a low SOC. Looking back on old SMT screenshots I saw a 2mV difference with the car around 6k miles, a lot of 4mV reading and then 6mV becoming more common.

Based on your observations maybe 80% is "good enough?"

 

[Feathermerchant]

Thanks for this post @Feathermerchant. Interesting and helpful. If you can confirm a few things, 80% SOC might be good enough to keep the battery pack in decent BMS balance.

A few questions for you:

• How often do you charge beyond 90%? Almost never. Sometimes on road trips.
• Do you let the car sleep for 4-6 hrs often at various SOC levels (especially if you charge to 90 or beyond)? We only charge past 90% and let it sit the night before a road trip.
• Do you let the car sample various SOC levels? ? Sometimes the car sits at various charge levels at or below 80%
• What's your low end SOC you try to hit for sampling? I have not engaged in sampling.

 

[jgt1942]

Hey everyone,
I finally got around to updating the balancing video - thanks for being patient.
Check out the corrected version below that describes the use of "bleed resistors" to balance the pack.

The concepts are similar to my previous video. Previously, I incorrectly suggested the pack is balanced while still connected to the charger.
In reality, a sufficiently high state of charge only triggers the BMS to begin balancing. But the balancing process will very slowly continue long after you've left the charger.

Thanks for a GREAT video!!!
At the end of Aug I picked up my used 2020 M3 Long Range AWD Dual motors and drove it home from the Raleigh NC Tesla store to my home in Oak Island NC (about 138 miles) when I arrived home I only had 7 miles of range left. At this time, being new to a Tesla. I did not question the range. Recently I charged to 100%, and planned a trip from Oak Island, to Pinehurst NC, then to Raleigh NC. Per the range estimate, I should arrive in Raleigh with 40-50 miles of range left. However, about 2/3 of the way a warning popped up informing me that I could not make it to my destination. I stopped at a supercharger (Sandford NC) and charged to 80% and continued my trip to Raleigh. The next day I left Raleigh and drove back to Pinehurst and then started the drive back to Oak Island. I was informed that I did not have enough battery to make it to a supercharger in Laurinburg. I reduced my speed to a max of 45 miles and made it to the charger with 3% remaining on the battery. I charged to 80% (stated that I had a range of 231 miles), went to a restaurant in the same area (about 200 feet) ate dinner, and continued the trip to Oak Island (about 95 miles away). I should have arrived with approximately 136 miles remaining. However, when I arrived home the range left was only 48 miles remaining.

On another local trip I left my house with an 80% charged battery. I drove to Wilmington NC and returned home, this was a total of 79 miles.
However, the car stated that I only had 43% charge remaining. This means that 37% of the battery was required to drive 79 miles.

I've gone in huge circles with Tesla on this issue with zero results. They claim that with the remote test, all is OK.

Suggestions??? BTW, I just set the charge to 100% and tomorrow I will drive to Myrtle Beach SC (total about 108 miles). Hopefully I will see an improvement in the actual range.

 

[BillLin]

@jgt1942 , you have provided nothing that can help evaluate your efficiency or lack thereof. Speed, temperature, cabin heating? What does the energy screen indicate for Watts per mile? If you haven't reset any of the trips, seeing what they currently indicate would be useful.

Edit: tire pressure?

 

[Rub"Y"]

Driving at night uses more battery life especially with high beams on. If it's cool where you are. Precondition before you leave this helps me a lot at least for the beginning of the trip.

 

[zroger73]

LED headlights use less than 50 watts.

Just the vehicle sitting there awake without being driven uses about 500 watts.

Driving at 65 MPH uses about 20,000 watts.

 

[Feathermerchant]

On vacation in Utah, I ran into a guy that said the car's range estimate was always way off. After quizzing him, I found out that he likes to drive considerably over the speed limit. I reminded him that the car's trip planning software assumes a speed slightly over the speed limit but not grossly over the speed limit. I think he understood after I explained it but was clueless before. I told him to use the estimated arrival charge on the display and set his speed accordingly. It's a great game to play.

We generally drive 5 over or so and always seem to arrive at our destination with plenty left.