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Range Loss Over Time, What Can Be Expected, Efficiency, How to Maintain Battery Health
- Thread starter KK_RedM3
- Start date
Candleflame
Active Member
yap, like i said, not displeased at all about it - even though the battery has been behaving quite well over the last 18 months. Worse for my colleague whos on 409km (gradual decline) without that error.
Now, given how my car was already a legacy car back in 2019 I do wonder if they put another 78.8kwh NCA battery in or maybe even a 82kwh NCM.
Wasnt there something that Tesla doesnt have access to 2170 cells anymore and only has 2170L cells available now and even old refurbished packs arent available anymore?
Candleflame
Active Member
Candleflame
Active Member
oh so there are no NMC packs which are 2170L?
edit: also spoke to my collegue and turns out he actually has the battery error too, he just thought he was out of warranty... :O
edit: also spoke to my collegue and turns out he actually has the battery error too, he just thought he was out of warranty... :O
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The L behind 2170 is only refering to the capacity.
Tesla/Panasonic designation for that new cell with 5% more capacity. The actual cell is the same size but bigger capacity.
The LG 2170 cells is called M48 and M50. ( no L)
In the EU certification the variant code for the car is:
3 = Panasonic
5 = LG
C = older smaller capacity (classic?)
L = newer larger ( Large?)
No designation= can be smaller or larger as both used the same desig initially.
3 in E3D is panasonic (can be either)
3L = panasonic 2170L (82.1 kWh)
3C = old panasonic 2170 (77.8 kWh)
5 in E5D is LG
5L = LG M50, 78.8 kWh
5C = LG M48 74.5kWh (not approved in a performance).
5 = could be any of them, probably = 5C
Candleflame
Active Member
i guess we are gonna find out in like 3 months. not sure how long itll take them to order one in or if they wanna keep me at bay with stupid charging routines for a while. that said i charged to 90% this morning and range dropped even further so i reckon only a matter of time before that cell kills the whole pack coz it cant be charged up.
IceMan8247
Member
Hey guys,
We've seen a lot of confusion regarding battery balancing vs. recalibration.
There are several cases recently where ultra-conservative daily charge limits (50-60%) caused pack imbalance on relatively new cars with Nickel cells, and 90% daily charge limits and pack balancing every 3-4 months are being recommended to keep the pack balanced.
We decided to make a video that goes deep into the science behind pack balancing and why its important.
Note:
- The car in the video is an early 2022 M3LR. Degradation improved from 2.5% to 1.7% after balancing (+3 miles)
We've seen a lot of confusion regarding battery balancing vs. recalibration.
There are several cases recently where ultra-conservative daily charge limits (50-60%) caused pack imbalance on relatively new cars with Nickel cells, and 90% daily charge limits and pack balancing every 3-4 months are being recommended to keep the pack balanced.
We decided to make a video that goes deep into the science behind pack balancing and why its important.
Note:
- The car in the video is an early 2022 M3LR. Degradation improved from 2.5% to 1.7% after balancing (+3 miles)
Candleflame
Active Member
No kidding, and your video leaves me more confused.
Has there been a change to the balancing logic as stated in the Model 3 service doc shown below? Does it actually balance while charging or only discharging via bleed resistors? Here’s a screen clip from a few years ago from @ord3r.
IceMan8247
Member
Thanks for sharing. I didn’t mean to add to the confusion….I was trying to help sort it out.No kidding, and your video leaves me more confused.
Has there been a change to the balancing logic as stated in the Model 3 service doc shown below? Does it actually balance while charging or only discharging via bleed resistors? Here’s a screen clip from a few years ago from @ord3r.
We used the article below as one of the sources for the video:
Tesla battery management system (BMS) calibration
Tesla battery management system (BMS) calibration instructions
tesla-info.com
Below is a snip from the article from April 2023:
Cell balancing
While the battery cells will sort themselves out up to a point if the car is simply left, there can still be some residual imbalance in the cells. To address this, the battery benefits from a 100% charge.- Plug the car in to charge, preferably on a AC charging point although you can also do this on a rapid chargerbut it may block it for others for some time.
- Set the charge limit to 100% and leave the car to charge.
- When the car reaches what appears to be 100% it may well say it has finished charging but it is drawing current. Leave the car charging until it indicates no energy is being added to the battery. This can take some time (an hour or so) after the car appears to have reached 100%. The charge rate may drop to under 10A which is fine. Let the car do what it needs to do.
- Eventually the battery will stop taking on current. Be mindful if you have the heating on, the car will still be taking current, but not for the purposes of charging the battery.
I have seen this same procedure recommended elsewhere to help fix an unbalanced pack. I believe it’s described in this video as well:
EDIT: Perhaps, based on the text you provided, charging up to 100% and waiting for current to stop (which may be long after the car says “charging complete”) allows more of the bricks to reach their absolute peak voltage. Then the bleed resistors are better able to perfectly balance the pack because a larger number of bricks had been fully topped off, allowing a high percentage of the pack’s bricks to be brought into alignment.
I suspect that using bleed resistors to bring the bricks into alignment will become increasingly more accurate as the SOC is increased due to the natural shape of the voltage vs. SOC curve (shown in the video). Balancing higher up on the “knee” of the curve where the voltage changes rapidly will result in brick’s SOC being better matched to each other. Trying to match individual bricks to a target SOC using their voltage will be less accurate lower on the curve in the flat region because the rate of change is so small.
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I’ve seen both of those but question their source material. There is a lot of advice and guidance available, but it is hard to discern what is accurate. Some is generic and not specific to the Tesla BMS. Others are for different vehicle configurations or are outdated based on hardware or software revisions. Other advice is provided by Tesla service techs with questionable interpretation or translation from documentation.
There are only a few people on this forum that have the credentials (@wk057), usually gained from deep testing or reverse engineering, that I’d trust beyond Tesla documentation. And Tesla documentation is not infallible either as it may refer to out-of-date configurations.
Bottomline, I didn’t think the Model 3 2170 battery pack had a means of applying selective current to specific bricks to null pack imbalance via charging. I thought it could only use the bleed resistors to remove charge from individual bricks. I’d love to learn more if someone has firsthand knowledge.
IceMan8247
Member
Well said. I bet you’re right - applying current to individual bricks would require a ton of hardware (isolated supplies for each brick for example). Using bleed resistors to drop bricks with the highest voltages back down into alignment would require considerably less hardware. Thanks for the feedback.
IceMan8247
Member
I just spoke with a colleague of mine with a lot of experience designing battery management systems. He said the “bleed resistors” referenced in that previous post are likely also used by the BMS as “shunt resistors” which can be switched across the highest voltage bricks during charging, bypassing charge current, which effectively charges up the lower voltage bricks to match the higher voltage bricks that are being shunted.
This is how they charge up selective low bricks to null pack imbalance during charging.
He was surprised to hear those resistors would be used to bleed down battery voltage while not charging, as it would be a waste of stored battery energy. Pretty much every BMS he has designed shunts current around high cells during charging, rather than bleeding off stored energy after charging.
It would certainly be interesting to hear from one of those guys you mentioned with first hand experience!
I would be surprised if he was charging large packs at 250kW... The resistors in the Tesla packs are nowhere near large enough to bypass charging current. And if they were they would need to have significant cooling added to them. It can take the bleed resitors days to balance a high brick of cells.
I think what it comes down to is if the pack was so out of balance that it required shunt resistor Tesla would declare the pack failed and replace it.
The Tesla BMS has no ability whatsoever to shunt current around bricks during charging.
The only control lever it can pull at the cell group level is to enable or disable 100mA of bleed resistors. They can only discharge groups. There's zero ability to charge them or bypass them or anything like that.
In fact, I'd have some serious doubts about this colleague's experience, at least with large EV packs, as no BMS that can bypass bricks during charging exists to the best of my knowledge. That'd require pretty massive hardware for every cell group and be insanely complex and expensive. You'd basically need contactors on every cell group.
Electrically you can't "bypass" a group with a resistor. This makes no sense. If you place a resistor across a group you're just discharging that group through the resistor, not bypassing anything.
No. If you're charging at say, 40A/240V/~10kW, you're getting ~25A DC at each cell group (current is constant in series). On the cell groups with balancers you're able to take 0.1A of that and bleed it as heat, so those get 24.9A instead of 25A. Basically a rounding error. Sure, a theoretical BMS could use more resistors to convert more incoming charge to heat... even 25A worth of resistors to make one group not charge at all by dissipating ~100W of heat from that group...... but no BMS does this. I could see something in say, an RC hobby lithium pack having bleed resistors that could offset a slow charge of an amp or so, but nothing like this exists in the EV space.
Since 100mA is peanuts in the face of 200,000 to 300,000 mAh cell groups, it's completely necessary for the Tesla BMS to enable them even when not charging to correct some imbalances. It'd take these bleed resistors nearly a week to correct a 2% imbalance! It takes about 9 months to fully discharge a pack starting at 100% charge using just the bleed resistors. (I've done this with packs that are simply unsafe to work on. Tesla even has an official procedure for this.)
Fortunately, Tesla builds the packs with very well matched original cells, so balancing is almost not even needed aside the occasional nudge to the higher cell groups. Generally deltas of less than 10mV in healthy packs. This is why hack jobs like module replacements and shops on YouTube claiming to "repair" modules by doing insane things like clipping cell fuses are 110% full of crap. The Tesla BMS has no ability to cope with modules that don't perfectly match up with the rest of the pack... as in, they need to be built and used together from day 1.
The bleed resistors serve several other purposes. Tesla's BMS uses these in clever ways to help measure cell group internal resistance, and even capacities on a per-group level, using a somewhat complex algo, down to about +/- 250 mAh... which is insanely impressive. They can use more clever methods to measure the sense line resistances, and almost immediately detect any event which causes a single cell fuse failure (as long as the BMS is active at the time.... if a shop that doesn't have a clue what they're doing snips a cell fuse and reinstalls, it'll take the BMS some time to realize it before your car's a paperweight).
Tesla's BMS is quite impressive. There's nothing like it on the market.
The only control lever it can pull at the cell group level is to enable or disable 100mA of bleed resistors. They can only discharge groups. There's zero ability to charge them or bypass them or anything like that.
In fact, I'd have some serious doubts about this colleague's experience, at least with large EV packs, as no BMS that can bypass bricks during charging exists to the best of my knowledge. That'd require pretty massive hardware for every cell group and be insanely complex and expensive. You'd basically need contactors on every cell group.
Electrically you can't "bypass" a group with a resistor. This makes no sense. If you place a resistor across a group you're just discharging that group through the resistor, not bypassing anything.
No. If you're charging at say, 40A/240V/~10kW, you're getting ~25A DC at each cell group (current is constant in series). On the cell groups with balancers you're able to take 0.1A of that and bleed it as heat, so those get 24.9A instead of 25A. Basically a rounding error. Sure, a theoretical BMS could use more resistors to convert more incoming charge to heat... even 25A worth of resistors to make one group not charge at all by dissipating ~100W of heat from that group...... but no BMS does this. I could see something in say, an RC hobby lithium pack having bleed resistors that could offset a slow charge of an amp or so, but nothing like this exists in the EV space.
Since 100mA is peanuts in the face of 200,000 to 300,000 mAh cell groups, it's completely necessary for the Tesla BMS to enable them even when not charging to correct some imbalances. It'd take these bleed resistors nearly a week to correct a 2% imbalance! It takes about 9 months to fully discharge a pack starting at 100% charge using just the bleed resistors. (I've done this with packs that are simply unsafe to work on. Tesla even has an official procedure for this.)
Fortunately, Tesla builds the packs with very well matched original cells, so balancing is almost not even needed aside the occasional nudge to the higher cell groups. Generally deltas of less than 10mV in healthy packs. This is why hack jobs like module replacements and shops on YouTube claiming to "repair" modules by doing insane things like clipping cell fuses are 110% full of crap. The Tesla BMS has no ability to cope with modules that don't perfectly match up with the rest of the pack... as in, they need to be built and used together from day 1.
The bleed resistors serve several other purposes. Tesla's BMS uses these in clever ways to help measure cell group internal resistance, and even capacities on a per-group level, using a somewhat complex algo, down to about +/- 250 mAh... which is insanely impressive. They can use more clever methods to measure the sense line resistances, and almost immediately detect any event which causes a single cell fuse failure (as long as the BMS is active at the time.... if a shop that doesn't have a clue what they're doing snips a cell fuse and reinstalls, it'll take the BMS some time to realize it before your car's a paperweight).
Tesla's BMS is quite impressive. There's nothing like it on the market.
IceMan8247
Member
Wow thanks for the detailed response!
Clearly you know your stuff!
I truly appreciate the education.
And while bleed resitors waste stored energy, shunt resitors waste charging energy and thermal management energy.
IceMan8247
Member
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