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.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.
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.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?
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.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?
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.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.
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.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.
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.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.
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.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.
Very interesting.. LEAF wont have any warranty issues due to coolant leaks inside the battery caseIn 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.
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?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.
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.That said, does anyone know what the upper threshold temp of this chemistry battery?
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?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."