What if Nissan had engineered the LEAF BMS like the Volt?

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RegGuheert

Well-known member
Joined
Mar 19, 2012
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Location
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I have been thinking about the many statements I have read to the effect that the battery in the Chevy Volt has not lost any capacity. I will state up front that it seems very clear: the 2011 Chevy Volts do not appear to have lost any range. It is also clear that they have not lost any available battery capacity. I will also state up front that this does NOT mean that the batteries in the Chevy Volts have not lost any capacity.

So how is this possible, given what we see with other EVs? It seems clear that they have engineered it this way to give their customers a better user experience. Here is a recent quote from GM-Volt.com referencing an apparent GM design decision:
larry4pyro at gmvolt said:
I remember an Autoline episode just after GM announced they were going ahead with the Volt where a GM battery engineer stated that the Volt is being designed to still provide about 40 miles of range "at the end of battery life". That left quite an impression on me. My Volt will be 2 years old in a couple of weeks and I see no reduction in range from this time last year.
I think it would be interesting to explore what the LEAF and the discussions in this community would be like had Nissan taken this approach, but still chose not to include a TMS:

Revised 2011 Nissan LEAF Specifications:
- Battery capacity: 24kWh
- Available battery capacity: 15.75 kWh
- EPA Range: 55 miles
- Nissan Range (TM): About 60 miles

Sales Statistics:
Sales of the Nissan LEAF would be well below their current levels. Many people would have simply decided that a car with a 55 or 60 mile range would not work for them.

What Nissan LEAF owners are saying about their car after two years of ownership:
- JailorSFGuy in Seattle writes: It's amazing! After two years and 50,000 miles of driving, the LEAF still goes exactly as far as it went the day I brought it home!
- azpre in AZ writes: It seems that Elon Musk was wrong about the LEAF battery not holding up in AZ without a TMS! Just like the Volt owners in AZ, our range has not changed since day one, yet we do not experience the big drop in range in the summertime they see due to the operation of their battery's TMS.
- LEAFplan in AZ writes: I have honed my hypermiling skills over many years and I have applied this knowledge to break through the magical 100-mile LEAF range barrier.

What's really happening:
- The batteries in AZ would be degrading in the LEAF just as they actually did, but no one would have hit the limit yet since cycling losses would have been limited significantly.
- This coming summer, the LEAF range in AZ would finally start to drop and likely would drop precipitously.

So, what do I take from this thought experiment?
- It seems clear why the Volt owners' experiences have been so universally positive to date.
- It also seems clear that a similar approach to the LEAF would have only kept perceptions positive for a while, but would not have prevented what happened last summer.
- No, I don't think Volt owners in AZ will deal with what LEAF owners in AZ dealt with last year, since the Volt has a battery TMS. However, I also don't think Volt owners will make it through their warranty period in AZ without a battery replacement. Fortunately, it is covered!
- Many of us who enjoy driving our EVs 75 miles or more would not be doing so had Nissan taken this approach.
- Most importantly, it will take a bit more time before we start to see the leading edge of Chevy Volt range degradation. I cannot easily predict when that will happen, but I will guess it will take about two more years. We'll see.
 
Remember that in addition to TMS (very helpful) the Volt battery is "over-sized". The nominal 16kWh size is the minimum needed to get the full $7,500 federal tax credit (GM was involved in getting the legislation pushed through). **BUT** less than 2/3 of the nominal capacity is available capacity. The Volt battery is engineered to not discharge much below 23%, nor higher than 87% (these % are approximate from what I remember reading, but pretty close). It is this limiting of DOD (Depth-of-Discharge) and avoidance of the upper and lower SOCs that are the most useful.

Now imagine, as nominal capacity window degrades (shrinks), that the BMS (software) can manipulate to keep the available capacity window the same size :D
 
RegGuheert said:
What Nissan LEAF owners are saying about their car after two years of ownership:
- JailorSFGuy in Seattle writes: It's amazing! After two years and 50,000 miles of driving, the LEAF still goes exactly as far as it went the day I brought it home!
No - the 55 mile "Leaf" wouldn't have worked for Taylor (Not Jailor, BTW).
 
RegGuheert said:
evnow said:
No - the 55 mile "Leaf" wouldn't have worked for Taylor (Not Jailor, BTW).
Right! That's why I changed the name and lowered the number of miles driven.
His nick is based on Taylor Shellfish Farms, and I believe he commutes from Kent, WA to the Shelton, WA. It's somewhere between 63 to 65 miles one way. He got level 2 charging installed there. Just a quick comment about the topic of this thread: the usable capacity of the Volt has been confirmed to be almost exactly half of the LEAF (10.4 vs 21 kWh) in 2011/2012 vehicles. GM increased battery capacity by about 0.5 kW in 2013 through a "chemistry tweak". A few Volt drivers can get over 50 EV miles with careful driving. Their number could be greater than the number of people in the 100-mile club with the LEAF. I remember a discussion on the Volt forum, where someone mentioned that the Volt pack had three cells in parallel, and the LEAF only two. This supposedly helped reduce the current through individual cells, facilitated more even heating and aging. I will try to locate the post, and link it here. Would you have link to Steve's (TaylorSFGuy) statement that his LEAF goes as far today as it did two years ago? He is essentially running a cycle life test of the battery in a near ideal climate. It's certainly very interesting data.
 
surfingslovak said:
Just a quick comment about the topic of this thread: the usable capacity of the Volt has been confirmed to be almost exactly half of the LEAF (10.4 vs 21 kWh) in 2011/2012 vehicles.
I used EXACTLY the same ratio of available capacity to total capacity for the hypothetical LEAF as GM did for the Volt (but I based it 10.5 kWh for the Volt, 10.4).
surfingslovak said:
Would you have link to Steve's (TaylorSFGuy) statement that his LEAF goes as far today as it did two years ago?
No. As far as I know, he never said any such thing.

Just to be clear, this is all hypothetical assuming the BMS were like the one in the Volt. I have read several threads about range over on GM-Volt and they read similarly. My point is we would be the same here had Nissan done this.
 
my theory is that the Volt's BMS goes more off of miles primarily rather than purely Voltage, typcially, giving it what appears to be a very consistent all electric range when in reality the depth of discharge and the exact point of hand off to the generator/motor fluctuates depending on demands and secondarily, voltage drop. given there is so much wiggle room, using what, only one third of the true capacity, it is hard to really measure range loss. Actually, if I'm correct, it's brilliant with respect to abolishing range anxiety in terms of daily driving as well as long term range capacity loss anxiety.

the Volt may look like a better example of how TMS protects the battery than it really is... that aside, TMS is still essential, IMHO and the Leaf's lack there of is it's main Achilles heel. future EV batteries will be large enough to treat more like the Volt's, shallow mid pack cycling that varies some depending on demands with an attempt to give a consistent available range in miles rather than emphasizing remaining capacity ... peace of mind is worth it's weight in gold, something Volt owners have more of than Leaf owners.

without some breakthrough in chemistry with respect to heat tolerance, I suspect the Leaf will be the last EV made without TMS.
 
RegGuheert said:
evnow said:
No - the 55 mile "Leaf" wouldn't have worked for Taylor (Not Jailor, BTW).
Right! That's why I changed the name and lowered the number of miles driven.
Not sure that makes sense to me. You need to show that people who are cribbing now - would have been happy, in the same scenarios.

I for one wouldn't have bought a 55 EPA mile Leaf. So for the happiness of some desert dwellers - who went against advice from people like me to lease rather than buy - a large number of wouldn't have bought a Leaf.
 
evnow said:
Not sure that makes sense to me. You need to show that people who are cribbing now - would have been happy, in the same scenarios.
That's not what I'm trying to show. In fact, I stated that I thought sales would be much lower than they have been. Regarding AZ folks, I don't think this solves anything for them either. It only delays the inevitable.

But as of today, anyone who had bought one of these fictitious LEAFs two years ago would be unaware that the battery had degraded at all and certainly wouldn't know how much it had degraded. That realization would come later. Just like it will come later for Volt owners.
 
Reg, great thread. Yes, I got the "hypothetical" aspect right away, including the psuedo-names. :D

Perhaps I, and others like me, are in fact running your hypothetical experiment right now. No, I don't have TMS, but I do park outside at night in the summertime (desert cooling). In addition, in the summertime I often ride my bicycle instead of driving, and leave the Leaf in the shaded garage. I've only seen 7 temp bars after a QC trip and it's 4 bars from Nov-Mar, 5 bars most of the rest of the year. I keep the batteries charged between 4-7 bars almost exclusively. Once in a while I mess up and it drops to 2 bars. Only a couple of times have I charged above 8 bars and not been able to drive off right away. I have probably charged to 100% less than 10 times. I did one 850 mi trip with multiple QC's, so that's one deviation. Finally, all of my daily driving is on city streets with slow acceleration/deceleration. Probably less than 10-20 trips at highway speeds.

Because I purchased and want it to last 20+ yr, I'm driving this car mostly without using the upper and lower battery ranges. As the battery degrades, I will start using more and more of the capacity. I bought assuming the 100 mi range was marketing and real range would be lower. Assuming 70-80% capacity at 8 yr (from marketing), I thought (worst case) I might have 50% capacity at 16 yr and 30% (7 kWh) capacity at 24 yr. Since I typically get 7-8 yrs on my Pb acid batteries in this climate, I think I'll do better than average with the Li ion ones.

My driving varies from 2.5 mi/kWh (winter with heat on) to 6 (summer). I should still have 15-30 mi range in 20+yr, which will still meet my in town driving needs. Is it crazy to think that I'll have the same EV in 2033? Probably, but then again I still use a Pentium computer with Win95 (upgraded from Win3.11) for non-internet stuff.:eek:

So, yes, I am running your thought experiment, and loving it. The Leaf is great, it exceeds my daily driving needs by 5-10x. It has a great BMS & TMS (sitting above my shoulders) and will meet my needs for years. If anything, I have to make excuses for longer drives. This past winter we added several nights out (dinner and a show) in a neighboring town just because. If there was charging in downtown Walla Walla (not at the Nissan dealership) about 130 mi RT, then we could do the same thing there.
 
Reddy said:
Because I purchased and want it to last 20+ yr, I'm driving this car mostly without using the upper and lower battery ranges.
It is not clear whether Li ion will last that long. Not even sure they last 10 years.

Good news is that you can get one quite cheap by then.
 
evnow said:
Reddy said:
Because I purchased and want it to last 20+ yr, I'm driving this car mostly without using the upper and lower battery ranges.
It is not clear whether Li ion will last that long. Not even sure they last 10 years.

Good news is that you can get one quite cheap by then.
People from the Volt forum have quoted from a reliable GM Engineering source who had said that they expect the Volt battery to last 15 years in cooler climates and 12 years in hot climates.
 
evnow said:
Reddy said:
Because I purchased and want it to last 20+ yr, I'm driving this car mostly without using the upper and lower battery ranges.
It is not clear whether Li ion will last that long. Not even sure they last 10 years.
It's not clear to me either, but I'd like to give it a try! I was surprised to learn from the How long did/will you keep your LEAF? survey that there are 7 other crazy people on here shooting for the same thing.
 
Volusiano said:
People from the Volt forum have quoted from a reliable GM Engineering source who had said that they expect the Volt battery to last 15 years in cooler climates and 12 years in hot climates.
Well, that is all assuming the accelerated tests actually represent reality. Who knows ?
 
Consider that the Volt battery has TMS and is also not used to the charge and discharge extremes that the Leaf battery is. Thus, I would expect it to last much longer than the Leaf battery.

Volusiano said:
People from the Volt forum have quoted from a reliable GM Engineering source who had said that they expect the Volt battery to last 15 years in cooler climates and 12 years in hot climates.
 
RegGuheert said:
evnow said:
Reddy said:
Because I purchased and want it to last 20+ yr, I'm driving this car mostly without using the upper and lower battery ranges.
It is not clear whether Li ion will last that long. Not even sure they last 10 years.
It's not clear to me either, but I'd like to give it a try! I was surprised to learn from the How long did/will you keep your LEAF? survey that there are 7 other crazy people on here shooting for the same thing.
Thanks, I must have missed that thread. Well, I can't say I'll make it, but there's hoping. I have a 12 yr old laptop with the original Li battery that only runs about 20 min (down from 3 hrs originally). Certainly, it's effectively useless but I'm pretty sure the excess heat and 100% charge (I've always run it plugged in like a desktop machine) was really it's downfall. I hope the Leaf battery does better.
 
Volusiano said:
People from the Volt forum have quoted from a reliable GM Engineering source who had said that they expect the Volt battery to last 15 years in cooler climates and 12 years in hot climates.
If that's to 70%, then that's great news. I think most of the industry says end of life at 70-80% capacity. Again, if I can get 8 yr to 70%, then why not 15 yr to 50%? Unless there are major chemical failures (dendritic shorting). Who knows how long-lived these batteries will be compared to ones produced even 10 years ago? I certainly don't. I'm able to accept 50% capacity and won't sell until somewhere below that point.

Sure, if Nissan adds a couple of DCQCs out here in the sticks, and provides a new 40 kWh battery for $5000 before 2020, I'll immediately stop this experiment, and take the new, higher capacity pack. Heck, I might even sell my '92 ICE (nah, only kidding, it's still got another 30 yr left in it).
 
Getting back OT, I think a 50 mi Leaf with "hidden" capacity, that would be slowly released to the user every year would have resulted in a significant reduction in sales. Even in my small town, many people talk about driving 80-100 mi/day (everyone seems to be ferrying kids around to multiple school events). Many on this forum report pushing the current Leaf's limits just on the daily commute. If we'd only had 50 mi to begin with, many people just would not have bought the pure BEV. Yes, the average is around 40-45 mi/day, but averages don't work for this application.

I think GM got it right when they provided enough EV miles to cover the "average", and then the gas burner backup for the longer days. That gives people the full EV experience, most of the time. It's working. The EV project data are showing that Volt drivers plug in 1.4 times/day vs 1.1 for Leafs. They love EV driving so much that they are willing to plug in more than once a day (effectively doubling the amount of time spent "fueling up" compared to us Leafers).

I also think Nissan got it right when they provided about 2x the average miles. This provides 80-90% of the population the ability to drive BEV 80-90% of the time. Maybe it's even a higher percentage, but I won't quibble over exact numbers. Many people have other cars so the extra 10-20% isn't an issue. Sure, we all want more range (have you ever seen a dog only use 1/2 the leash length???), but most of the time what we have is sufficient. That said, if Nissan doesn't improve the range by 2015, they will lose customers to other companies.

Also, in other threads, people have postulated about whether Nissan is really hiding some extra capacity (especially with respect to the Phoenix battery degradation and the 9 bar warranty). I recall reading about a battery bar reset. Certainly it possible, but I don't think we will ever know for sure.

So, IMHO, Americans will accept a 40-50 mi PHEV, but not a 50 mi BEV.
 
batteryproblemmnl
Reddy said:
Reg, great thread. Yes, I got the "hypothetical" aspect right away, including the psuedo-names. :D
I just had time to read the thread in its entirety, sorry for being slow. Cute, including the faux nicks. Unfortunately, the essential premise of thread, that GM is in fact compensating all of the battery capacity loss by releasing reserve capacity is not proven. It's been talked about, certainly, and it would make sense, but it's not something that can be taken for granted.

As it happens, several months before the first loss of range reports showed up on the forum, I conducted my own informal survey. I looked at the available data for the Roadster, the MINI E, and some other EVs to get an idea what drivers saw in the field. Although it's based on anecdotal reports and a small sample, there was nobody who claimed 8% range loss after the first year. Nobody. Please recall, that this is considered to be Nissan Normal (TM), per the chart TickTock shared with us last year.

I think the magnitude of the decline was the real surprise, and if you could hide some of it, then that might be helpful when it comes to meeting customer expectations. I believe most owners assume that the decline will be linear. I agree with this part of the thought experiment. In fact, I remember reading that it was an accepted practice with hybrids. That said, I believe that the capacity fade seen with AESC batteries is large, and it could be mitigated by chemistry tweaks, cell composition changes, a TMS or some other more effective cooling type, other than passive air.

Perhaps I'm wrong, but I'm simply not willing to accept 8% capacity loss in the first year as "normal". No matter what Nissan might think or say about it publicly. Battery capacity padding makes sense in this scenario, but it will only get you so far. Adding more capacity and range, even without hiding it, would have prevented a lot of the heartache and complaints also. One of the fundamental problems with the LEAF is that many perceive its range as very limited. And any unexpected and significant loss is considered unacceptable.

The problem for Nissan is that a 55-mile EV wouldn't meet the sales targets for the LEAF. Adding more capacity would make the car more expensive, and impact the sales volume as well. Personally, I believe that it would be better to attack the root of the evil: rapid degradation. Perhaps a combination of the two approaches is better and more acceptable, and maybe that's what GM has been doing with the Volt.
 
surfingslovak said:
I just had time to read the thread in its entirety, sorry for being slow. Cute, including the faux nicks. Unfortunately, the essential premise of thread, that GM is in fact compensating battery capacity loss by releasing reserve capacity is not proven. It's been talked about, certainly, and it would make sense, but it's not something that can be taken for granted.
Agreed. But when I went through this thought experiment with the LEAF, I realized that even though the LEAF has quite substantial range loss to date, such an approach would have likely kept it completely hidden from view, even until now. Since the Volt uses a substantially similar chemistry to the LEAF, it seems clear that they felt a TMS system was critical to coddle the battery as much as possible. But a TMS cannot prevent battery degradation of this chemistry. It can only reduce it.

So by thinking this idea through for the LEAF, it became clear to me that we would be having a similar experience to the Volt folks had Nissan done this. To me, that gives a lot of credence to the idea that GM actually used this approach. In other words, it is now my mental model for how the Chevy Volt works. As such, I will be looking for the day when range starts to degrade on those cars. Until that happens, we really cannot know how quickly their batteries are degrading. I simply do not accept the idea that the Volt batteries have not degraded at all in 35,000 miles.
surfingslovak said:
Perhaps I'm wrong, but I'm simply not willing to accept 8% capacity loss in the first year as "normal". No matter what Nissan might think or say about it publicly. I think padding capacity makes sense in this scenario, but it is only get you that far. Adding more capacity and range would have prevented a lot of the heartache and complaints also. It would be better to attack the root of the evil though: rapid degradation. Perhaps a combination of the two approaches would be better and more acceptable.
Don't get me wrong. I'm not trying to defend Nissan's approach of not using a TMS or even suggesting that this approach to BMS would have been a good idea. Even though I like the LEAF without TMS for our personal application, I think the combination of no TMS and such a fragile battery chemistry is a real issue for some areas, and I have been as vocal as anyone regarding that issue, at least early on. But I also feel that the right battery chemistry can work without TMS, even in very hot and cold climates. Nissan took a risky approach with this battery chemistry, but even with its warts, it has proven to be a very safe and reliable component in the LEAF. Unlike some EVs ;) , it hasn't left too many owners stranded! If they can continue to build market share as they steadily improve their chemistry for better stability and capacity, they may come out O.K.

I will say it's good to have choices in the market. Eventually I do expect certain approaches to win the lion's share of the market. I'm betting no TMS will be the long-term winner in EVs, but that is definitely NOT a given. I wonder if this idea of hiding battery capacity losses will also become standard. If you combine it with higher capacity batteries, it has some nice features that would certainly improve the ownership experience for many, not the least of which are improved overall life and more predictable range. The big downside for BEVs is the idea of being stranded on the side of the road when there is still some usable capacity in the battery. Perhaps there could be a limited emergency mode that could be activated for those cases.
 
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