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NISSAN LEAF 62Kwh
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Discussion Starter #1
(Copied from TWITTER with thanks – the Images are the copyright property of MUXSAN)

The back ground to is that the 40Kwh LEAF is being used as a taxi, it’s covered 200,000 Km’s (124,000 miles) in 2 years (or less) and has been continually Rapid Charged.

The car was reporting isolation issues so MUXSAN suspecting water ingress into the battery case so took a look inside and the images show what they found. According to MUXSAN this is very rare and by any means, not typical.

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That's quite worrying. The protection system is supposed to stop battery over heating anyway.

Wonder if the 60s are more or less prone to this?
 

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That's quite worrying. The protection system is supposed to stop battery over heating anyway.

Wonder if the 60s are more or less prone to this?
But thanks to the #Rapidgate campaign Nissan reduced the degree of protection. Obviously at extremes this can be an issue.
As an aside, what would you think that the average life of an ICE engine used as a taxi will be for the current crop of cars? I think that a significant number will fail at a lower mileage.
 

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I have used Leafspy on 5 Leaf's used as Taxis. 1x 24kWh, 3x 30kWh & 1x 40kWh mileage between 50-90k - SOH on all of them was above 88% IIRC. They were mostly rapid charged with no issues, in fact the drivers I spoke to didn't even know about 'Rapidgate'! I'm sure Nissan (and all manufacturers) must stress test the packs far in excess of what would be expected regular use, and whilst that sort or mileage with exclusive rapid charges is not exactly 'regular' I still think there may be another explanation for such extreme failure in this case, otherwise we'd be seeing this happening on some cars at lower mileages too in hotter climates.
 

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I wonder if the temperature sensor failed or something so it got too hot.

I know it's out of warranty now but if the consumer laws are like the UK then Nissan should still contribute towards a new pack.
 

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This is what happens when a software "fix" for rapidgate allows the battery to charge faster at higher temperatures - customers are "happy" because the charge rate doesn't drop like it used to, (to them rapidgate is fixed) but the battery is being severely punished for it. You can't bend the laws of physics...

Of course this is an extreme example, however the fact that the BMS allowed the battery to get hot enough on an ongoing basis that the cells all warped all out of shape shows either there is inadequate temperature monitoring (only 3 sensors for 192 cells, so some hot spots in stressed/degraded cells may be missed in the monitoring) or the BMS is simply not doing enough to restrict use (charge and discharge rates) when the cells are too hot. Probably a bit of both. Ouch.
 

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I wonder if the temperature sensor failed or something so it got too hot.

I know it's out of warranty now but if the consumer laws are like the UK then Nissan should still contribute towards a new pack.
The car was sold without the normal warranty under a special deal to be a taxi. Personally I don't think that the failure is unreasonable - as I said previously modern ICE don't survive well at that mileage.
 

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The car was sold without the normal warranty under a special deal to be a taxi. Personally I don't think that the failure is unreasonable - as I said previously modern ICE don't survive well at that mileage.
Perhaps not "unreasonable" if the car was genuinely flogged to death, but certainly avoidable if the battery had active cooling, better temperature monitoring and/or stricter controls on charge/discharge rates with temperature, or all of the above.

EV's should be striving to surpass the reliability and longevity of ICE vehicles, not barely draw even with them.

I guess Nissan just don't want to be seen selling a car that refuses to drive or charge at all because it has overheated - they'd rather make the BMS more lenient and pick up the slack in warranty replacement of the battery (and cross their fingers most abused batteries last beyond the warranty period and become the owners problem) than lose face and admit that they engineered a car which allows the battery to be punished in this way.
 

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It might be out of warranty but imagine the hoohah if nissan shrug and do nothing. It's in their best interests to fix it cheaply and not let on how many warped battery packs they've mended.

The arizona Leafs shot them in the arse and they didn't learn. They still haven't. It wouldn't be that difficult to even have a air cooling system like the Soul EV had. Draw air in from the cabin and over the battery and push it out of the back.
 

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NISSAN LEAF 62Kwh
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Discussion Starter #13
What I found with the 40Kwh LEAF, that having driven say 200 miles and on the second rapid charge, the battery temperature would move into the red sector of the temperature gauge (50°c as verified by LEAFSPY). To protect the battery, I would then drive at 58mph behind a wagon and that would quickly drop the battery temperature down 4 or 5°c and prevent the vehicle going in restricted drive power mode (not desirable on the motorway)

On the 3rd rapid charge it would RAPIDGATE to protect the battery and would restrict the charge to say 14 / 16 Kw's but in a battery hovering about 45°c, that is still a lot of energy and heat going into the battery. Consistently heating the battery up to 50°c is too much heat on a regular basis, its probably okay 4 or 5 times a year like I did. A battery with cooling, the BMS would be looking to maintain a maximum temperature of about 38°c and realistically a battery should not be subjected to more than this to maintain longevity.

But get a taxi driver who doesn't even know where the temperature gauge is, it's continually rapid charged and when this drivers shift ends, then another driver takes the vehicle over for another shift. The battery doesn't even get to cool over night.

All those rapid charges causes build ups on the battery anode resulting eventually in short circuiting, which looking at the damage is what has happened here.
 

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I don't think it's just the 40kWh that pushes the cell temperatures hard either.

I recently acquired a 30kWh and it charges flat out all the way to about 85%. (Quite impressed by the charge speed in fact) I found that while efficient motorway driving only raised the cell temperatures about 4C, a single rapid charge from 30% to 85% raised it by a further 12C, so it's rapid charging, not driving (unless you're driving like an idiot) that really pushes the cell temperatures.

On one trip (ambient about 20C) I started with the battery at 19C, drove until I was down to 30%, the battery was by then 23C, however the 20 minute rapid charge that followed pushed it up to 35C.

40C is about the maximum I'd be comfortable seeing the cells at for longevity and degradation reasons. A second stretch of motorway driving is going to be nudging near 38C and a second rapid charge unless it throttled the speed (which the 30kWh doesn't seem to do on a second charge) will be pushing it well into the high 40's if not 50C...beyond comfort for more than very occasional use.

From that experience I would say that if you start with a cool battery, a motorway stretch followed by a single rapid charge followed by another motorway stretch is OK and not going to be harmful, however a second rapid charge in a row is pushing the cells well into "don't do that too often" temperatures, even though the car might be letting you do it without throttling the charge rate. It's up to individual drivers whether they want to push the battery temperature this high or not. If you do find yourself having to rapid charge multiple times in a row, on the 2nd and subsequent charges don't go past 80% as damage to the cells caused by heat will be reduced (but not eliminated) by keeping the SoC below about 80%. (And don't put it on charge as soon as you get home - let it cool down first. The charge timer is great for that)

However if you find yourself in the situation of having to do two or more rapid charges in a row in a Leaf any more than occasionally you've probably bought the wrong car! (I bought one being aware of the thermal limitations and knowing that my use case of mainly commuting and charging at home on a charge timer would not push the battery hard)
 

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Not sure if it's down to thermals alone. Pouch cells can swell for may reasons. We have a small batteries for retaining data on servers, they tend to last around 2 to 3 years before swelling so badly that they bend the circuit board they're attached to. They're in a controlled environment and won't be getting hotter than about 25'C
These batteries are left at high states of charge for long periods of time, only being discharged as part of a monthly capacity "learn cycle".

At least the Leaf detected the isolation fault so everyone knew to be a but more cautious with the car.
 

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Discussion Starter #17
From what I read on the twitter post and the terminology used, I assumed that the vehicle would not rapid charge because the CHAdeMO charger could not get past the insulation test it performs on the hand shake. The guy at Muxsan, thought this was caused by water ingress into the battery pack, then found the real reason. Just how I interpreted it, unless anybody’s has a different angle.
 

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Not sure if it's down to thermals alone. Pouch cells can swell for may reasons. We have a small batteries for retaining data on servers, they tend to last around 2 to 3 years before swelling so badly that they bend the circuit board they're attached to. They're in a controlled environment and won't be getting hotter than about 25'C
These batteries are left at high states of charge for long periods of time, only being discharged as part of a monthly capacity "learn cycle".

At least the Leaf detected the isolation fault so everyone knew to be a but more cautious with the car.
High temperature alone won't cause swelling, but high charge/discharge while hot will. Common with overheated cells on quadcopters etc when subject to high charge/discharge rates while too hot.

For most of the cells to suffer from the same swelling it's not a faulty cell, (unless its a design flaw) it's a systemic environment problem. Probably a combination of too high a charge/discharge rate at high cell temperatures.

While rapid charging speeds are limited at high cell temperatures, discharge during driving is not limited until significantly higher temperatures, and this discharge heats the cells just as much as charge for the same rate.

Perhaps the owner did a lot of rapid charging and drove it like they stole it on the motorway ?
 

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In relation to the discussion about high rapid charging temperatures, I thought this was quite interesting:


We all know that the 30kWh model charges the fastest of the Leaf's and hardly tapers until right near the end, and also that it can get very hot on multiple rapids. (well over 50C)

Well, this enterprising lot in New Zealand decided to do their own custom firmware version to introduce some high temperature throttling of rapid charging speeds similar to that of the 40kWh model - although not as severe as the early firmware versions of the 40kWh model.

Up to 40C charge speeds are not affected, but beyond that they are progressively throttled, whereas the normal 30kWh firmware doesn't throttle until something like 50-55C.

Given the choice between a rapid charge on a hot battery taking 20 minutes and causing the battery to overheat and waiting 30 minutes, I'd take the latter.

Pity the firmware modification is only available in NZ...
 

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That really is a dramatic failure!

I'm genuinely curious to know what would happen to that car if the driver kept using it.

Would a fire be the end result? Or would the battery just go weak across enough cells, turtle/low power mode triggered permanently?
 
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