tbleakne
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Re: Nissan buys back my Leaf

Tue Aug 27, 2013 1:54 pm

Weatherman wrote:
jstack6 wrote:Imagine how much extra energy is used for the battery cooling. I have both a 2013 LEAF and a Focus EV that has cooling. On 120 the Focus can either cool or charge but not both. So on a hot day in the sun you may get very little charging done. On 240 it blows and expels so much heat I can't park it in the garage, I have to leave it outside. I've tried to calculate the energy used for cooling but don't have a good method. In general it seems to be almost twice as much.


I have a Volt and it spends a fair amount of time cooling the battery, but it doesn't use anywhere near twice as much energy as my LEAF. Maybe 10-15% more. Considering the LEAF battery temp hovers in the 90s and the Volt is trying to keep its battery temp somewhere in the 70s, that's not too bad.

(Obviously, the hotter the climate, the more energy the car would use to keep the battery cool.)

Right now I am spending as much or more energy trying to keep my Leaf cool by air conditioning my garage as I spend on charging it. This helps somewhat in my mild SoCal climate, but it would be completely impractical in AZ. Obviously external cooling of the whole car (and garage) is much less efficient than a simple cooling loop threaded through the battery just like the car's charger has. I believe extending the existing cooling system to include the battery need not raise maintenance costs much.

The Tesla Roadster spent a lot of energy on battery cooling when the car was parked, but it looks like the Model S, with improved chemistry, only rarely actively cools the battery while parked and plugged in. They still have a very effective battery cooling system that gets used a lot while driving and Supercharging.
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TimLee
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Re: Nissan buys back my Leaf

Wed Aug 28, 2013 7:02 am

hyperlexis wrote:Why would having a battery cooling system result in high maintenance costs? -- it's no more than a larger radiator system filled with coolant and an electric water pump and thermostats. It's not freon based, correct? And even if it were, so what? Right now the Leaf has just such a system, except it only sends coolant to the charger to cool it down, back in the trunk. It would be far, far cheaper to have to flush the long-life coolant once in 10 years than to need to replace a cooked battery pack in three.

No, an effective battery Temperature Management System will not be just heat transfer to the ambient temperature through water coolant through a radiator. That works for cooling the inverter and on board charger, which only need to stay cooler than a relatively high temperature a few degrees hotter than ambient.
But the serious impacts from battery heat probably start around 90F (32C). To keep the battery to that kind of temperature, you have to have an AC type system, using some type of phase change fluid such as "freon".
Now that could be done. But it becomes pretty costly and problematic to expect the vehicle to use such a system 80% of the time for 4 to 6 months of the year in Phoenix. Especially problematic when you're trying to keep the vehicle cost down like Nissan is with a very modest 24 kWh battery size. You'll need to have it plugged in a lot more than you do just for driving the vehicle.
If the new "Hot" battery, which they are doing accelerated aging tests on at a constant battery temperature of 113F (45C) achieves reasonable battery life in Phoenix (say 6+ years) and gets to 10+ years in mid range climates, and 15+ or maybe 20+ year life in Pacific Northwest / Canada / Norway, that will probably be the better more cost effective engineering solution.
The concept is good if the battery life is sufficient. They just badly missed it on battery degradation rates for the 2011 / 2012 battery, and probably for the 2013 slightly improved chemistry battery too. They just need to make the new "Hot" battery work, and try to make a reasonable fix for all the people they leased or sold the 2011 / 2012 / 2013 LEAF to. Before they become like the old GM and kill the electric car for a second time.

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hyperlexis
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Re: Nissan buys back my Leaf

Wed Aug 28, 2013 9:44 am

TimLee wrote:
hyperlexis wrote:Why would having a battery cooling system result in high maintenance costs? -- it's no more than a larger radiator system filled with coolant and an electric water pump and thermostats. It's not freon based, correct? And even if it were, so what? Right now the Leaf has just such a system, except it only sends coolant to the charger to cool it down, back in the trunk. It would be far, far cheaper to have to flush the long-life coolant once in 10 years than to need to replace a cooked battery pack in three.

No, an effective battery Temperature Management System will not be just heat transfer to the ambient temperature through water coolant through a radiator. That works for cooling the inverter and on board charger, which only need to stay cooler than a relatively high temperature a few degrees hotter than ambient.
But the serious impacts from battery heat probably start around 90F (32C). To keep the battery to that kind of temperature, you have to have an AC type system, using some type of phase change fluid such as "freon".
Now that could be done. But it becomes pretty costly and problematic to expect the vehicle to use such a system 80% of the time for 4 to 6 months of the year in Phoenix. Especially problematic when you're trying to keep the vehicle cost down like Nissan is with a very modest 24 kWh battery size. You'll need to have it plugged in a lot more than you do just for driving the vehicle.
If the new "Hot" battery, which they are doing accelerated aging tests on at a constant battery temperature of 113F (45C) achieves reasonable battery life in Phoenix (say 6+ years) and gets to 10+ years in mid range climates, and 15+ or maybe 20+ year life in Pacific Northwest / Canada / Norway, that will probably be the better more cost effective engineering solution.
The concept is good if the battery life is sufficient. They just badly missed it on battery degradation rates for the 2011 / 2012 battery, and probably for the 2013 slightly improved chemistry battery too. They just need to make the new "Hot" battery work, and try to make a reasonable fix for all the people they leased or sold the 2011 / 2012 / 2013 LEAF to. Before they become like the old GM and kill the electric car for a second time.


Do other EVs with battery cooling use a Freon-based system or a coolant based one? 90 degrees is really not that bad, and certainly a coolant-based system could handle that. An auto engine gets much hotter than that, over 212 degrees, and uses a coolant-based system. And, frankly, even if a Freon based cooling system was needed, which I don't believe it would be, a sealed, electrically driven compressor system should be pretty reliable. Many vehicles, including the Prius, use an electric compressor for its AC system, and its been pretty darned reliable. Most home AC units, sealed and electrically driven compressors, last for decades without problems. It's the standard, belt driven systems used in conventional vehicles which have more problems. An electric compressor system would actually be more reliable.

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TonyWilliams
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Re: Nissan buys back my Leaf

Wed Aug 28, 2013 9:50 am

hyperlexis wrote:... I'm sure the batteries must cost less than a whole new car, but still the thought crossed my mind -- like a PC with a sealed-in battery (MacBook, Surface....), is it cheaper to throw the whole thing out rather than repair??????

I shudder to think it could be the case.


They don't throw the car away... they buy it back specifically because they don't want it "Lemon Law'd" (which would require disclosures to the sucker who eventually buys the car).

All the cars would be sold to unsuspecting customers with no idea of its past problems.

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TonyWilliams
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Re: Nissan buys back my Leaf

Wed Aug 28, 2013 9:53 am

hyperlexis wrote: An electric compressor system would actually be more reliable.


The LEAF, just like every modern EV, has an electric powered air conditioner compressor. Yes, it could (and should) be used to cool the battery.

edatoakrun
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Re: Nissan buys back my Leaf

Wed Aug 28, 2013 10:25 am

TimLee wrote:
hyperlexis wrote:Why would having a battery cooling system result in high maintenance costs? -- it's no more than a larger radiator system filled with coolant and an electric water pump and thermostats. It's not freon based, correct? And even if it were, so what? Right now the Leaf has just such a system, except it only sends coolant to the charger to cool it down, back in the trunk. It would be far, far cheaper to have to flush the long-life coolant once in 10 years than to need to replace a cooked battery pack in three.

No, an effective battery Temperature Management System will not be just heat transfer to the ambient temperature through water coolant through a radiator. That works for cooling the inverter and on board charger, which only need to stay cooler than a relatively high temperature a few degrees hotter than ambient....


IMO, if you want a truly scary picture of ATM's potential complexity and costs, look no further the Chevy Volt:

http://gm-volt.com/2010/12/09/the-chevr ... explained/

There really is little question that all BEV batteries will be passively or semi-passively cooled (by fans and/or airflow while driving) at some point in the near-future.

I have always believed that Nissan probably made the correct decision to skip the transitional liquid-cooled-by-AC ATM technology, which is cost-effective only for batteries that are both very expensive and very delicate, neither of which we should expect in the future.

If the new heat-resistant battery lives up to Nissan's projections, and comes out only ~ one year from now, the proof of the superiority of Nissan's approach over that taken by virtually all other BEV manufactures will have come even earlier than I expected.
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Weatherman
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Re: Nissan buys back my Leaf

Wed Aug 28, 2013 10:32 am

edatoakrun wrote:If the new heat-resistant battery lives up to Nissan's projections, and comes out only ~ one year from now, the proof of the superiority of Nissan's approach over that taken by virtually all other BEV manufactures will have come even earlier than I expected.


This is an interesting point.

If Nissan really has something, which is going to make TMSs obsolete, why are they being so quiet about it (only revealing a few details to a small group of invitees to a Phoenix meeting)?

(By the way... I happen to think their approach is smart. They don't really want another PR failure on their hands.)
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TimLee
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Re: Nissan buys back my Leaf

Wed Aug 28, 2013 11:26 am

hyperlexis wrote:Do other EVs with battery cooling use a Freon-based system or a coolant based one? 90 degrees is really not that bad, and certainly a coolant-based system could handle that. An auto engine gets much hotter than that, over 212 degrees, and uses a coolant-based system. And, frankly, even if a Freon based cooling system was needed, which I don't believe it would be, a sealed, electrically driven compressor system should be pretty reliable. Many vehicles, including the Prius, use an electric compressor for its AC system, and its been pretty darned reliable. Most home AC units, sealed and electrically driven compressors, last for decades without problems. It's the standard, belt driven systems used in conventional vehicles which have more problems. An electric compressor system would actually be more reliable.

I don't know the specific answer to your first question.
But if they want to maintain a temperature such as 90 F (32 C) they cannot do that with just a coolant based system. To achieve a temperature colder than the ambient, you have to generate a temperature colder than that and you also have to generate a temperature hotter than the ambient so you can get rid of the heat. Typically done with a Freon based system. The Freon evaporates (boils) at a temperature lower than the colder than ambient temperature you need, and when it is compressed it heats up to a temperature significantly higher than the ambient where it can reject the heat to the ambient as it condenses.
I agree that electric compressors are very efficient and reliable, such as the 2013 SV & SL LEAF heat pump system. The 2011 / 2012 / 2013 S AC only systems are also pretty efficient. But based on my experience the AC cooling of the LEAF while parked does use around one of twelve bars of battery charge per hour under 90 F to 95 F ambient conditions. I'm a bit surprised it is that high, because each status of charge bar is ~ 21.5 / 12 = 1.8 kWh. But the LEAF display is usually only showing 500 to 700 W power draw under these conditions. But it can initially pull 3 kW to 4.5 kW briefly when first turning in on with the cabin very hot. A battery cooling box system might use quite a bit less than the vehicle cabin cooling. But you are going to have to do more charging to power it than a non TMS system.

edatoakrun wrote:There really is little question that all BEV batteries will be passively or semi-passively cooled (by fans and/or airflow while driving) at some point in the near-future.

I agree that all BEV batteries will have some form of cooling. The LEAF does have passive cooling with some air flow across the bottom of the steel battery box while driving. Even with the "Hot" battery, Nissan maybe should consider a forced air flow system. They're testing at 113 F (45 C) continuous battery temperature. But in Phoenix with heat radiation from a hot blacktop parking lot in direct sun with the vehicle windows closed, the cabin and eventually the battery itself may hit 10 F to 15 F above the ambient. A lot hotter than what they're testing. Throw in a DCQC shortly after letting the battery heat soak all day, and you've got maybe 25 F above ambient. :( :o :shock:

Edit: Original posting of "into and out of the" corrected to "across the bottom of the steel".
Last edited by TimLee on Thu Aug 29, 2013 1:00 pm, edited 1 time in total.

Tim Lee
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davewill
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Re: Nissan buys back my Leaf

Wed Aug 28, 2013 2:38 pm

TimLee wrote:... The LEAF does have passive cooling with some air flow into and out of the battery box while driving. Even with the "Hot" battery, Nissan maybe should consider a forced air flow system. ...:
Nope. The battery box is sealed. No air flow at all.
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Berlino
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Re: Nissan buys back my Leaf

Wed Aug 28, 2013 2:49 pm

davewill wrote:
Nope. The battery box is sealed. No air flow at all.


Sealed as it may be, air flow does impact the battery's temperature.

This is most evident when there's a large difference between outside and pack temperatures. This may not occur often in San Diego, but this month where I live it it can be 88F in the day, but 50F at night. A battery in a LEAF at rest that's at 86F will slowly cool off when the outside temp is in the 50's, but quickly become colder once you start driving, so air is working its way in there somehow.
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