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

Fri Mar 29, 2013 7:55 am

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 wrote: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.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

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Re: What if Nissan had engineered the LEAF BMS like the Volt

Fri Mar 29, 2013 9:18 am

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
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Lost CapacityBar 6/6/13 @34,173 miles while in LEAF Battery Monitor: 83.41%, 71.4F (avg); cool overnight;

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evnow
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Re: What if Nissan had engineered the LEAF BMS like the Volt

Fri Mar 29, 2013 9:44 am

RegGuheert wrote: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).
1st Leaf : 2/28/2011 to 5/6/2013
2nd Leaf : 5/4/2013 to 3/21/2017
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RegGuheert
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Re: What if Nissan had engineered the LEAF BMS like the Volt

Fri Mar 29, 2013 9:45 am

evnow wrote: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.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

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surfingslovak
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Re: What if Nissan had engineered the LEAF BMS like the Volt

Fri Mar 29, 2013 9:58 am

RegGuheert wrote:
evnow wrote: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.

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RegGuheert
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Re: What if Nissan had engineered the LEAF BMS like the Volt

Fri Mar 29, 2013 10:13 am

surfingslovak wrote: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 wrote: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.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

GaslessInSeattle
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Re: What if Nissan had engineered the LEAF BMS like the Volt

Fri Mar 29, 2013 10:49 am

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.
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evnow
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Re: What if Nissan had engineered the LEAF BMS like the Volt

Fri Mar 29, 2013 2:10 pm

RegGuheert wrote:
evnow wrote: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.
1st Leaf : 2/28/2011 to 5/6/2013
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RegGuheert
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Re: What if Nissan had engineered the LEAF BMS like the Volt

Fri Mar 29, 2013 2:30 pm

evnow wrote: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.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

Reddy
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Re: What if Nissan had engineered the LEAF BMS like the Volt

Fri Mar 29, 2013 3:47 pm

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.:o

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
2011 SL; 9 bar, 45.80 AHr; 45,000 mi; rcv'd Aug 18, 2011
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