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Richard, a couple of questions..

a. Nissan has repeatedly said that they use "laminated" cells, what do they mean?

b. they use a liquid electrolyte in the pouch cells?.. how do they vacuum seal the plastic pouches with liquid inside them?
 

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Richard,
Thx for the graph of life vs temp.

You mention that the Leaf pack may be uninsulated. It seems that in the situation where the car is parked over some heat soaked pavement and allowed to sit or say in stop and go traffic this lack of insulation would be a detriment. It might be more efficient from a heat transfer POV to insulate the compartment and use convective heat transfer to cool the pack. Also, I am not sure where the pack gets its cooling air.---from the cabin or outside ambient.
 

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Given the fact that: (1) GM has spent a lot of EMD on a TMS for their 16 KWh battery pack, and (2) they are confident enough to warranty it for 8 years, added to which is (3) they've been testing it in death valley...I'm betting they understand that keeping the battery within an allowable temperature range is rather important to life. If fact, I'm guessing the Volt's TMS is a competitive advantage for them.

To which, I'm also rather confident that should the battery temp reach an upper threshold, the TMS will come on keep it with-in the allowable limits, regardless of whether or not it is plugged in or not.

However, once the SOC reaches a min level, all bets are off. It's trade offs at that point, which has the least impact to battery life -- battery temp or SOC?
 

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On Star

Perhaps the Volt will be smart enough to send you an email via On Star to tell you to keep the vehicle on Mountain Mode if you not going to plug it in during the heat of the day so the TMS will have enough juice to keep the battery with-in temperature specs...else you will void your warranty?
 

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I wonder how many BTU's it takes tochange the volts battery pack 1 deg F. It's not free energy you know you either pay in gasoline mileage or kwh out of the grid.
 

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Discussion Starter #26
Richard,
Thx for the graph of life vs temp.

You mention that the Leaf pack may be uninsulated. It seems that in the situation where the car is parked over some heat soaked pavement and allowed to sit or say in stop and go traffic this lack of insulation would be a detriment. It might be more efficient from a heat transfer POV to insulate the compartment and use convective heat transfer to cool the pack. Also, I am not sure where the pack gets its cooling air.---from the cabin or outside ambient.
Insulation works well for an active TMS, where you can actually control the temperature inside the battery compartment through active heating and cooling. Insulation enhances the energy efficiency of such a system. But I would think that insulation is kind of a double-edged sword for a passive design like that in the Leaf, where on the one hand it can slow the rate of undesirable heat gain *in*, but on the other hand, it also slows the rate of dissipation of undesirable heat *out*. My understanding is that the Leaf’s passive cooling works via conduction and radiation, not convection. But I could be wrong. I believe that the Leaf’s battery compartment is environmentally sealed and that there is no air exchange with the outside (either with cabin air or outside ambient air). My understanding is that there is one small fan inside the battery compartment that circulates the air in order to evenly distribute the heat throughout the battery compartment. That eliminates hot spots, or at least reduces temperature gradients within the battery compartment, making dissipative cooling easier and more uniform, for heat to be conducted and then radiated outwards. That’s my understanding of how it works anyway, but as I said, I could be wrong.
 

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Discussion Starter #27
Given the fact that: (1) GM has spent a lot of EMD on a TMS for their 16 KWh battery pack, and (2) they are confident enough to warranty it for 8 years, added to which is (3) they've been testing it in death valley...I'm betting they understand that keeping the battery within an allowable temperature range is rather important to life. If fact, I'm guessing the Volt's TMS is a competitive advantage for them.

To which, I'm also rather confident that should the battery temp reach an upper threshold, the TMS will come on keep it with-in the allowable limits, regardless of whether or not it is plugged in or not.

However, once the SOC reaches a min level, all bets are off. It's trade offs at that point, which has the least impact to battery life -- battery temp or SOC?
Per the previous discussion in this thread, from what GM has said, the TMS does not come on when the car is off and not plugged in. But as has been pointed out, that is almost 2-year old information, so it’s quite possible that GM has moved in the last year and a half to correct that design deficiency through further development of the TMS. (One would certainly hope so.) However, even if GM has not corrected this design flaw in the TMS, there is a simple enough workaround for us here in our hot climate. We will just leave the car turned on all day long at work. This is actually what we have to sometimes do with our Toyota RAV4-EVs, because they have this same problem and design flaw of the TMS not being able to operate when the car is turned off. So we carry two keys for the car, one which we leave in the start switch (I won’t call it “ignition”, since it’s an EV) to leave the car turned on, with the doors locked, and the other which we carry with us, to be able to unlock the door and get back in the car.

Temperature has a much greater effect on battery life than SOC. SOC does have an effect, but in the opposite direction of what you might think. For lithium batteries -- and *only* for lithium batteries (this does not apply to NiMH and lead-acid) -- a lower average SOC (to a point, down to 30% SOC) over time will result in a longer battery life, and a higher average SOC over time will result in a shorter battery life.
 

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Discussion Starter #28
Perhaps the Volt will be smart enough to send you an email via On Star to tell you to keep the vehicle on Mountain Mode if you not going to plug it in during the heat of the day so the TMS will have enough juice to keep the battery with-in temperature specs...else you will void your warranty?
That’s a good idea, one that I had thought of some time ago. But, at least from what we know at this point (based on almost 2-year old information from GM), you will also have to leave the car turned on during the day, all day long, and carry a second key to be able to unlock the door so you can get back in the car. This is something that I already have to do with my current electric car, so it’s not a big deal, but this is a design flaw that hopefully GM will have corrected by the time the Volt goes into production in just a few weeks.
 

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Discussion Starter #29
I wonder how many BTU's it takes tochange the volts battery pack 1 deg F. It's not free energy you know you either pay in gasoline mileage or kwh out of the grid.
It’s a pretty simple, straightforward financial cost analysis which shows that the economics strongly favor an active-cooled TMS over a passive-cooled design for an EV in a hot climate that is subject to daily solar loading.

For an EV with a passive-cooled/dissipative design, with daily solar loading at 120-140F and battery temps reaching 105-115F, the effective long-term average temperature of the batteries in my climate is around 95F, which results in about a 4 and a half year life for lithium-manganese batteries.

For an EV with an active-cooled TMS, like the Volt, which keeps the batteries at an average temperature of 71F, that will result in an 8 year life for a lithium-manganese battery pack, which is 3 and a half years longer than for a passive-cooled design. For a $10,000 battery pack like that in the Volt, the pro-rated cost of having to replace the battery pack 3 and a half years earlier is $4,375.

A highly efficient, active-cooled TMS for a battery pack the size of that in the Volt (16kWh), for the same parameters (i.e. to keep the battery pack at 71F in a hot climate with solar loading), can be designed to run on about 60 Watts. (I don’t know and am not saying that that’s the energy consumption of the Volt’s TMS, but I am involved in the design of similar active-cooled thermal management systems for EVs in a hot climate which achieve that level of energy consumption.) That aggregates to 1.44 kWh/day, for a total of 526 kWh/year, which costs $63.12/year, for a total of $505 over 8 years.

So the cost trade-off is a total of $505 over 8 years for the energy to run an active-cooled TMS that will achieve an 8 year life in a hot climate with daily solar loading, versus $4,375 to replace the battery pack 3 and a half years earlier in an EV without an active-cooled TMS that uses a simple passive-cooled/dissipative design.
 

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So the cost trade-off is a total of $505 over 8 years for the energy to run an active-cooled TMS that will achieve an 8 year life in a hot climate with daily solar loading, versus $4,375 to replace the battery pack 3 and a half years earlier in an EV without an active-cooled TMS that uses a simple passive-cooled/dissipative design.
But the consumer doesn't directly bear that cost. The warranty does. If what you say is how it works out, it'll be interesting to see how that works out for the Leaf.
 

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The LEAFs bettery has been designed for fast charge, that implies low IR losses and thus low heat production when the car is running.. but it cant get away from the slow heating up due to the Arizona sun..

George, stick a thermometer under a car that has been parked all day long, and let us know.
 

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Discussion Starter #32
But the consumer doesn't directly bear that cost. The warranty does. If what you say is how it works out, it'll be interesting to see how that works out for the Leaf.
Yes, good point to make that distinction. I was doing a basic, general comparative analysis of relative costs. Those costs have to be borne by someone. But you’re right that who bears the cost will be different in the two cases, in that it’s the EV owner who will have to bear the energy cost of running an active-cooled TMS, while it’s the OEM that will have to bear the warranty cost of early battery pack replacement.

Nissan knows and acknowledges that they’re going to have to replace battery packs early, under warranty, in hot climates. (I’ve been in meetings with fleet customers in hot climates where I’ve seen Nissan tell them to expect a 4 to 5 year battery pack life, which is why Nissan is urging them to take the Leaf on a 3-year lease, rather than purchase.) Nissan has done their own financial cost-benefit/trade-off analysis whereby they determined that it will be cheaper for them to replace a few battery packs early, under warranty, in those few hot-climate areas of the country, for those few customers who don’t take the hint to take the Leaf on a 3-year lease rather than purchase, than it would have been for them to design, engineer, develop, and manufacture a sophisticated and relatively expensive active-cooled TMS, especially when most of the country probably won’t need it (as much). (It’s just in really hot climates where the economics strongly favor going with an active-cooled TMS.) For Nissan, it was simply a cold, hard-nosed business decision. There are reasons why the Volt costs $8,220 more than the Leaf.

The great thing is that we’re now finally starting to get some choices in EVs. People can do their research and analysis on the Leaf and the Volt and choose that one which best meets their needs and suits their particular circumstances, including climate factors. To be quite honest about it, as someone who has been driving a pure BEV for several years now, I am philosophically and ideologically more inclined towards pure BEVs than PHEVs like the Volt. If I lived someplace like Seattle, or coastal regions of California where it never gets above 70 degrees F, I think I would probably be buying a Leaf rather than a Volt. But because I live in a hot climate, and the Leaf’s passive cooling just isn’t up to the task for this climate, I am buying a Volt rather than a Leaf. The Volt is a much better designed and engineered EV that better suits the requirements of my climate than the Leaf.

In the final analysis, Nissan’s decision to forgo an active TMS for the first generation of the Leaf was really one of expediency that was driven by competitive time-to-market pressures, to shorten the development cycle (in which Nissan was already a few years behind GM and playing catch-up) and bring the Leaf to market at the same time as the Volt. More recently, Nissan has admitted that the lack of an active TMS is a shortcoming that will be corrected in the next major model upgrade to the Leaf, likely in 2013, which will have an active TMS.
 

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Discussion Starter #33
The LEAFs bettery has been designed for fast charge, that implies low IR losses and thus low heat production when the car is running.. but it cant get away from the slow heating up due to the Arizona sun..

George, stick a thermometer under a car that has been parked all day long, and let us know.
Unless George has got a car that is an EV with a battery pack underneath the passenger cabin, sticking a thermometer under his car probably won’t tell you as much as someone who does have an EV with a battery pack underneath the passenger cabin, as I do, with our Toyota RAV4-EVs, similar in that respect to the Leaf. I see the battery temps get up into the 105-115F range when the car has been parked baking in the hot South Florida sun. This is why we often leave the car turned on (with the key in the start switch and the doors locked) -- because the RAV4-EV’s forced-air cooling system can at least bring the battery temps down below the environmental temperature (ambient + solar loading) of 105-115F, down to ambient, at 95F, although of course it can’t lower the battery temps below ambient.
 

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Discussion Starter #34
Here’s a quote from Volt Chief Engineer Andrew Farah relevant to this discussion:

One disappointment is that the Volt and other Lithium-ion battery-powered electric vehicles may not be viable in hotter climates, such as some states in the American Southwest. Despite the fact that Volts will be sold in these states, performance may be significantly undermined due to the heat. Volt Chief Engineer Andrew Farah describes, “The Volt may not be right for everyone. If you live in the Southwest, depending on how you use your car, the Volt might not be right for you.”

http://www.dailytech.com/Chevy+Volt+Cant+Handle+Hot+Southwest+but+Otherwise+is+Looking+Good/article16969.htm
 

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In the final analysis, Nissan’s decision to forgo an active TMS for the first generation of the Leaf was really one of expediency that was driven by competitive time-to-market pressures, to shorten the development cycle (in which Nissan was already a few years behind GM and playing catch-up) and bring the Leaf to market at the same time as the Volt. More recently, Nissan has admitted that the lack of an active TMS is a shortcoming that will be corrected in the next major model upgrade to the Leaf, likely in 2013, which will have an active TMS.
Very interesting.. LEAF wont have any warranty issues due to coolant leaks inside the battery case :)

How much energy would it take to route cold air from the LEAF's AC into the battery case?.. perhaps a diverter air valve that would not air condition the inside of the car while its parked but keeps the battery cool instead?

BTW, do you know if Nissan is using electrical heaters in the LEAF's battery case?
 

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It’s a pretty simple, straightforward financial cost analysis which shows that the economics strongly favor an active-cooled TMS over a passive-cooled design for an EV in a hot climate that is subject to daily solar loading.

For an EV with a passive-cooled/dissipative design, with daily solar loading at 120-140F and battery temps reaching 105-115F, the effective long-term average temperature of the batteries in my climate is around 95F, which results in about a 4 and a half year life for lithium-manganese batteries.

For an EV with an active-cooled TMS, like the Volt, which keeps the batteries at an average temperature of 71F, that will result in an 8 year life for a lithium-manganese battery pack, which is 3 and a half years longer than for a passive-cooled design. For a $10,000 battery pack like that in the Volt, the pro-rated cost of having to replace the battery pack 3 and a half years earlier is $4,375.

A highly efficient, active-cooled TMS for a battery pack the size of that in the Volt (16kWh), for the same parameters (i.e. to keep the battery pack at 71F in a hot climate with solar loading), can be designed to run on about 60 Watts. (I don’t know and am not saying that that’s the energy consumption of the Volt’s TMS, but I am involved in the design of similar active-cooled thermal management systems for EVs in a hot climate which achieve that level of energy consumption.) That aggregates to 1.44 kWh/day, for a total of 526 kWh/year, which costs $63.12/year, for a total of $505 over 8 years.

So the cost trade-off is a total of $505 over 8 years for the energy to run an active-cooled TMS that will achieve an 8 year life in a hot climate with daily solar loading, versus $4,375 to replace the battery pack 3 and a half years earlier in an EV without an active-cooled TMS that uses a simple passive-cooled/dissipative design.
Good information, but why would GM keep the battery at 71 deg F, the optimum battery temp? I would think the TMS would keep it just below the upper threshold temp to minimize power draw when the Volt is not plugged in, which I assume is higher than 71 deg F. That said, does anyone know what the upper threshold temp of this chemistry battery?
 

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That said, does anyone know what the upper threshold temp of this chemistry battery?
Upper temperature for what? I'm not an expert on this particular chemistry. What I've seen for cell phone Li-Ion cells is -20C to +60C operating and storage (maybeb a bit more for storage), and 0C to 45C charging. I've certainly had my cell phone refuse to charge when left in the car for over temp. How the Leaf's going to deal with a sub 120F charging temperature max is going to be interesting, since ambient in Phoenix can easily be that.

Li-Ion batteries have a tendency to engage in spontaneous rapid dissasembly if you try to charge them at high temp.
 

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Discussion Starter #39
Here are some additional articles and quotes relevant to this discussion.

First, read this entire article:

www.wired.com/autopia/2010/01/nissan-leaf-2/

Then, here are some excerpts and quotes from additional articles:

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Ford says that they chose to go with active liquid cooling (and heating) for the Focus Electric because proper thermal management of lithium-ion batteries is critical to the success of plug-ins and "extreme temperatures can affect performance, reliability, safety and durability."

"All-electric vehicles do not have a conventional engine on board, so it is critical we maximize the performance of the battery under various operating temperatures," said Sherif Marakby, Ford director, Electrification Program and Engineering, in a statement. "Active liquid systems are more effective than air systems at regulating lithium-ion battery temperature. As a result, the active liquid system on Focus Electric will play a key role in providing our customers with the best performance possible."

The Focus Electric will be much the same size as the Nissan Leaf and, Ford claims, will have a similar 100 mile range. But it's this issue of battery thermal regulation that has taken center stage recently as one of the key market differentiators for this first crop of plug-ins. The Nissan LEAF's battery has been called out as being “primitive” by Tesla CEO Elon Musk, and fears have been stoked that its battery will fail prematurely because it doesn't have active thermal management. It does have a passive thermal management system that is air cooled. However, the Volt has active liquid cooling and GM has used that pretty clearly as a way to say, and I paraphrase, "Our battery pack will last longer than the LEAF's."

...

Mark Perry, Nissan's director of product planning and marketing, has told me that eventually the LEAF's battery will get some kind of active thermal management, and that it is kind of a necessity for long term planning. It seems that the writing's on the wall and that active thermal management, especially of the liquid kind, is where all of this is headed.

www.plugincars.com/ford-focus-electric-will-get-liquid-cooled-battery-system-maximize-range-66496.html

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GM’s Volt executive Tony Posawatz explained why separate battery HVAC is so important in electric cars.

“Thermal management has bookend issues to manage: minimized power at low temperatures and life reduction at high exposure to higher temperatures,” he told Wired. “If you want to replace your battery every four to five years and someone is willing to pay for [a replacement battery], either the customer or the manufacturer, a modest or minimal HVAC system may work.”

http://gm-volt.com/2010/01/28/nissan-taking-shortcut-on-leaf-battery-no-thermal-management-system/

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GM-Volt.com: Achieving a ten year 150,000 mile goal is something it sounds like you’re very confident in now.

Bob Lutz: "Without committing to it being ten year or 150,000 warranty basically we are very very confident in the capability and the life of this battery in all but the hottest climates. So it could be that in certain very hot climates where people leave this thing in a baking supermarket parking lot all day, these lithium ion batteries, if they get much over 95 or 100 degrees Fahrenheit, they quickly start losing life. So we may have to adjust warrantees, but we really haven’t decided how to do that yet."

http://gm-volt.com/2010/05/03/bob-lutz-on-chevy-volt-pricing/
 

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Here are some additional articles and quotes relevant to this discussion.


GM-Volt.com: Achieving a ten year 150,000 mile goal is something it sounds like you’re very confident in now.

Bob Lutz: "Without committing to it being ten year or 150,000 warranty basically we are very very confident in the capability and the life of this battery in all but the hottest climates. So it could be that in certain very hot climates where people leave this thing in a baking supermarket parking lot all day, these lithium ion batteries, if they get much over 95 or 100 degrees Fahrenheit, they quickly start losing life. So we may have to adjust warrantees, but we really haven’t decided how to do that yet."

http://gm-volt.com/2010/05/03/bob-lutz-on-chevy-volt-pricing/
If you're plugged into the grid, but in the hot sun in AZ, it makes sense to have the TMS keep the battery at optimal temp because it can. However, if you not plugged, doesn't it still makes sense to have the TMS manage the battery temp as long as the battery has sufficient power available? However, rather than maintain the battery at it's optimal temp (which will use a lot of Watts); why not maintain it at the upper threshold temp (for example 85 degrees), which is warm but not enough to degrade the life of the battery (that's how I would define the upper temperature threshold). As soon as you power on the car, the ICE could be programed on to provide power to quickly lower the battery temp back down to the optimal temp?
 
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