Model Y Occasional 100 Percent charging

[William Taylor]

Hello,

A new and very happy owner of a MY Long range here in beautiful Anchorage Alaska!

To set up this question, I first have to say that I owned a 2022 Ioniq 5 SEL before purchasing the Model Y, and in the owners manual for the I5, It recommended charging it on AC level 2 power to 100 percent once a month or so to "Recalibrate the BMS system and allow for Cell balancing."

I combed through the Model Y owners manual and cannot seem to find something equivalent there. I know that Tesla has much more data than anyone else on battery management and maybe thats just Hyundai and their system being different.

With that being said, I am wondering, has anyone seen any information as to whether teslas need or would find utility in being charged to 100 percent on any kind of reoccurring basis, and does anyone do this?

 

[father_of_6]

Only LFP batteries seem to require an occasional 100% charge in order for the BMS to be able to keep track of the battery capacity, but Tesla hasn't yet produced a Model Y with an LFP battery (AFAIK).

 

[father_of_6]

Just want to add that for my Model 3, which has an NCA battery like yours, I charge it to 50% pretty much daily (sometimes if it's already close to 50% we don't bother plugging in). If I know tomorrow will be a heavy driving day, then I bump it up to something higher.

The reason for this is to minimize degradation. Not saying that charging higher will destroy your battery, just that if you want to absolutely baby the battery as much as possible, then setting it to 50% daily is the way to go. Of course, if that doesn't suite your driving needs then by all means set it to whatever you need.

Congratulations on the awesome vehicle!

 

[BitJam]

If you do charge to 100% (like at the start of a long road trip) it's best to leave it at 100% for as short a time as possible. The Scheduled Departure feature can help with this. Unfortunately, I think you need to let the car go to sleep for it to calibrate the battery so charging briefly to 100% won't help with calibration.

 

[Robocheme]

Only LFP batteries seem to require an occasional 100% charge in order for the BMS to be able to keep track of the battery capacity, but Tesla hasn't yet produced a Model Y with an LFP battery (AFAIK).

I remember reading somewhere that RWD MY's (made in China and Germany) had LFP batteries, but that AWD MY's did not. Interestingly, when I picked up my AWD MY last week the guy giving me the orientation said that I should charge the battery to 100% once a week. I was very surprised by this and I checked the details and my car definitely did not have a LFP battery. In other words, the guy may have assumed (incorrectly) that all MY's had LFP batteries or that even non-LFP batteries should be charged to 100% on a regular basis.

 

[father_of_6]

Interestingly, when I picked up my AWD MY last week the guy giving me the orientation said that I should charge the battery to 100% once a week.

Unsurprisingly, many of the sales employees don't know as much as the forum nerds. They'd have to really take an active interest in the cars, and I suspect most don't.

 

[father_of_6]

In other words, the guy may have assumed (incorrectly) that all MY's had LFP batteries or that even non-LFP batteries should be charged to 100% on a regular basis.

And really, I'm surprised this isn't already resolved in the software - e.g. a weekly'ish nagging reminder to charge to 100%.

Leaving it to employees to educate the consumer will definitely lead to misinformation.

One last thing perhaps worth mentioning for posterity (and just in case it wasn't already clear from @BitJam's post) is that it's still less healthy to charge an LFP battery to 100%, it's just needed in order for the battery management system to remain calibrated (and thus be able to accurately predict the remaining state of charge).

What's interesting is that the 2022 Ioniq 5 SEL appears to have an NMC, from a quick googling.

 

[kpanda17]

Battery Pack Rebalancing
I’m doing once a quarter
This is for Lithium Ion, MY, not LFP as they can be charged to 100% daily

Very good video explaining

 

[flixden]

Battery Pack Rebalancing
I’m doing once a quarter
This is for Lithium Ion, MY, not LFP as they can be charged to 100% daily

Very good video explaining

I am confused by the suggestion in the video to charge to 100%, then drive it down to 90% SOC, and then being done. Or does he let the car then sit at 90% for several hours?

 

[father_of_6]

I am confused by the suggestion in the video to charge to 100%, then drive it down to 90% SOC, and then being done. Or does he let the car then sit at 90% for several hours?

Pretty sure he's just saying "don't let the car sit at 100%"... but ideally you wouldn't let it sit at 90% either. This would be best done right before a LONG drive back down to 50%.

 

[Iron]

I am confused by the suggestion in the video to charge to 100%, then drive it down to 90% SOC, and then being done. Or does he let the car then sit at 90% for several hours?

Sorry to confuse things more, but I would let the car sleep for a few hours at 100% and 90 if normal charging is in the 50s or 60s percentage. This is specifically for recalibration purposes. Only occasionally, of course.

 

[father_of_6]

Sorry to confuse things more, but I would let the car sleep for a few hours at 100% and 90 if normal charging is in the 50s or 60s percentage. This is specifically for recalibration purposes. Only occasionally, of course.

At least in that video, it's recommended not to leave it at 100%.

My understanding is that just getting the SoC close to 100% gives the BMS the cell voltages it needs in order to detect and rectify any cell imbalances... it shouldn't need to stay at 100% for the actual "bleed off" to happen.

 

[IceMan8247]

At least in that video, it's recommended not to leave it at 100%.

My understanding is that just getting the SoC close to 100% gives the BMS the cell voltages it needs in order to detect and rectify any cell imbalances... it shouldn't need to stay at 100% for the actual "bleed off" to happen.

You are absolutely correct.

The video posted in this thread is mine and I would like to provide some additional detail below:

First off - I posted a slightly different version of this video onto this form a few months back, but it was quickly pointed out that I made several mistakes in explaining the BMS balancing process. I quickly removed the video from youtube because I didn't want to further confuse the topic. I finally got around to re-editing the video to fix the mistakes (based on feedback from some super smart dudes on this form).

There is an important point that I feel doesn't come across clearly in the video:
The BMS will be triggered to balance the bricks at states of charge under 100% (I couldn't find agreement on what exact SOC triggers balancing). This means for the vast majority of owners, their BMS will keep their bricks balanced, and their pack likely does not suffer from misalignment.
However, some owners with nickel cobalt cells use ultra-conservative daily charge limits (50% for example) which may not be high enough to ever trigger the BMS to balance their bricks. These packs may suffer from brick imbalance, and forcing their BMS to balance can bring their pack into alignment which may give back some lost range.

Bringing the pack up to 85%, or 90%, or 93%, or 95% is likely high enough to trigger the BMS to balance. As I say in the video, when I want to force my BMS to balance, I simply use the 100% setpoint because I know for a fact this will trigger balancing (somewhat lower setpoints may achieve the same result).
After bringing the pack up to 100%, I drive the car to bring the SOC down below 90%. Then over the next several hours (or days if the pack is very unbalanced), the bricks with the highest voltage will slowly bleed off just enough energy to bring the pack back into alignment. So to be clear, the balancing is not finished after reaching 100% or after driving down to 90%. The balancing has only just begun at that point.

And finally, I often hear that bringing the pack up to 100% does more harm than good. But for my car at least, this doesn't seem to be true. I've forced my pack to balance by using the 100% charge point several times, and I only have about 1.7% degradation (granted, at only 13K miles).

After making that video, I learned this is a sensitive topic with lots of different opinions. Hopefully that explanation helps clear it up.

 

[flixden]

You are absolutely correct.

The video posted in this thread is mine and I would like to provide some additional detail below:

First off - I posted a slightly different version of this video onto this form a few months back, but it was quickly pointed out that I made several mistakes in explaining the BMS balancing process. I quickly removed the video from youtube because I didn't want to further confuse the topic. I finally got around to re-editing the video to fix the mistakes (based on feedback from some super smart dudes on this form).

There is an important point that I feel doesn't come across clearly in the video:
The BMS will be triggered to balance the bricks at states of charge under 100% (I couldn't find agreement on what exact SOC triggers balancing). This means for the vast majority of owners, their BMS will keep their bricks balanced, and their pack likely does not suffer from misalignment.
However, some owners with nickel cobalt cells use ultra-conservative daily charge limits (50% for example) which may not be high enough to ever trigger the BMS to balance their bricks. These packs may suffer from brick imbalance, and forcing their BMS to balance can bring their pack into alignment which may give back some lost range.

Bringing the pack up to 85%, or 90%, or 93%, or 95% is likely high enough to trigger the BMS to balance. As I say in the video, when I want to force my BMS to balance, I simply use the 100% setpoint because I know for a fact this will trigger balancing (somewhat lower setpoints may achieve the same result).
After bringing the pack up to 100%, I drive the car to bring the SOC down below 90%. Then over the next several hours (or days if the pack is very unbalanced), the bricks with the highest voltage will slowly bleed off just enough energy to bring the pack back into alignment. So to be clear, the balancing is not finished after reaching 100% or after driving down to 90%. The balancing has only just begun at that point.

And finally, I often hear that bringing the pack up to 100% does more harm than good. But for my car at least, this doesn't seem to be true. I've forced my pack to balance by using the 100% charge point several times, and I only have about 1.7% degradation (granted, at only 13K miles).

After making that video, I learned this is a sensitive topic with lots of different opinions. Hopefully that explanation helps clear it up.

First of all: thanks! Lots of good info!

Now to my follow up question: how about charging to 100%, then immediately driving it down to 50% and letting it sit. Will it still do the balancing based on the data it has gathered when it was at 100%?
Nobody may know for sure, but I thought I'd ask ....

 

[IceMan8247]

First of all: thanks! Lots of good info!

Now to my follow up question: how about charging to 100%, then immediately driving it down to 50% and letting it sit. Will it still do the balancing based on the data it has gathered when it was at 100%?
Nobody may know for sure, but I thought I'd ask ....

Yeah that would work just fine.

Another nuanced detail that I thought was cool (again, from the smart reverse-engineer guys on this forum), is the bleed resistor control method is not closed-loop on brick voltage (I would have assumed the bleed resistors stay on until a particular brick voltage is reached). Instead, at the point of triggering the bleed resistors, the BMS looks at all of the voltages and determines the TIME each bleed resistor needs to be turned on to dump just enough energy to bring the bricks into alignment. Then the BMS keeps each bleed resistor on for that predetermined amount of time (time based rather than voltage based).

This is a super smart way to run the bleed resistors, because it means you can be driving the car with the pack under load (and the brick voltages swinging all over the place) while its balancing. If the BMS engaged the bleed resistors based on matching voltages, the car would have to be parked with no load on the pack for balancing to take place. But since the BMS runs each bleed resistor based on an amount of time that was determined at a no-load condition during charging, it doesn't matter if the car is driven or parked while the balancing takes place. I thought that was a pretty neat and nuanced detail.

It also means it doesn't matter which state-of-charge you decide to park your car at. By the time you get to 50%, the balancing may even be finished (assuming your pack wasn't very unbalanced to begin with).

 

[flixden]

Yeah that would work just fine.

Another nuanced detail that I thought was cool (again, from the smart reverse-engineer guys on this forum), is the bleed resistor control method is not closed-loop on brick voltage (I would have assumed the bleed resistors stay on until a particular brick voltage is reached). Instead, at the point of triggering the bleed resistors, the BMS looks at all of the voltages and determines the TIME each bleed resistor needs to be turned on to dump just enough energy to bring the bricks into alignment. Then the BMS keeps each bleed resistor on for that predetermined amount of time (time based rather than voltage based).

This is a super smart way to run the bleed resistors, because it means you can be driving the car with the pack under load (and the brick voltages swinging all over the place) while its balancing. If the BMS engaged the bleed resistors based on matching voltages, the car would have to be parked with no load on the pack for balancing to take place. But since the BMS runs each bleed resistor based on an amount of time that was determined at a no-load condition during charging, it doesn't matter if the car is driven or parked while the balancing takes place. I thought that was a pretty neat and nuanced detail.

It also means it doesn't matter which state-of-charge you decide to park your car at. By the time you get to 50%, the balancing may even be finished (assuming your pack wasn't very unbalanced to begin with).

Interesting!

If I understand this correctly, then all it would take for a balancing to be completed is a charge to 100% SOC (or close to it) every now and then, with no requirement of the car sitting at a certain SOC for some time.
Basically: have a longer trip planned? Charge to 100% shortly before you leave, then drive down the SOC. The cell balancing will be a welcome side effect.

 

[father_of_6]

Also, since the curve is only flat in the middle-ish, couldn't this rebalancing take place at the bottom end as well?

To me, this begs the question... if the curve is flat towards the middle, how does the BMS know the state of charge at all?

 

[IceMan8247]

Interesting!

If I understand this correctly, then all it would take for a balancing to be completed is a charge to 100% SOC (or close to it) every now and then, with no requirement of the car sitting at a certain SOC for some time.
Basically: have a longer trip planned? Charge to 100% shortly before you leave, then drive down the SOC. The cell balancing will be a welcome side effect.

Correct - you got it!

 

[IceMan8247]

Also, since the curve is only flat in the middle-ish, couldn't this rebalancing take place at the bottom end as well?

To me, this begs the question... if the curve is flat towards the middle, how does the BMS know the state of charge at all?

Good questions.....I drew that curve in excel, and exaggerated the flatness in an attempt to make the point clear.

If you look up actual lithium ion battery curves, you'll see they're not quite as flat as I drew it. So the BMS can still make a good guess at SOC in the mid-range, but the tolerance will always be much tighter near the top...and accuracy is paramount when balancing.

And yes, balancing at the bottom is called "bottom balancing" and can be done in certain battery pack applications. But it is my understanding that Tesla only does "top balancing."

 

[Tom Sagrak]

While reading this topic yesterday, I've charged my car to 100% and left about one hour later on a 450km trip (had to charge about 20% at a SUC) and now, I'm on 14% SoC. Should I leave the car overnight to let it (?) balance at this level, or charge it at my Wallbox to 50%?
And how can I see the results?

BTW - As far as I know if the SoC is less than 20% the car will not do any unnecessary energy spending (i.e. colling or heating the battery, etc.)