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Charles Murray
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Re: ALT is 104F, uhm.
Charles Murray   4/17/2013 6:15:58 PM
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That's an excellent point that has been largely overlooked in the discussion, ratsky. Location is key for these battery packs, especially if they are air-cooled.  

Charles Murray
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Re: ALT is 104F, uhm.
Charles Murray   4/17/2013 6:14:15 PM
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I don't think you're missing anything, Curious_Device. It's a harsh environment and it's very, very tough to predict the outcome using accelerated testing. People will debate this --and if they are qualified, we'll give them their due here -- but I think we won't really know the effects of every day wear and tear until we have about ten years of user experience to draw from.

Rob Spiegel
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Re: The batteries need to last
Rob Spiegel   4/17/2013 5:38:08 PM
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That's a great point, Chuck. Hurting the resale value of a vehicle hurts the overall value of the vehicle. It will be interesting to see how resale works with EVs.

Ratsky
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Platinum
Re: ALT is 104F, uhm.
Ratsky   4/17/2013 10:29:48 AM
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No, you're not.  However, there is another factor to consider: that  SAE number is really "under-hood" for a vehicle with IC engine.  The actual temperature extreme experienced by EV batteries will depend strongly on battery location within the vehicle structure and other factors of vehicle design.  Even so, "in-cabin" temperatures can easily hit the high 80s C range.  This is especially true for designs with large "greenhouses" and dark interiors.  Try touching the black dashboard of a car parked in Phoenix on a summer afternoon!  Third degree burns are likely.

curious_device
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Gold
ALT is 104F, uhm.
curious_device   4/17/2013 1:00:55 AM
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I understand that 104F is "above the mean temp", but 104F is nothing compared to summer heat soak temperatures of (112°C- according to SAE.)
Am I missing something or are they underestimating how harsh the EV battery environment really is?

Charles Murray
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Blogger
Re: The batteries need to last
Charles Murray   4/16/2013 7:08:28 PM
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I agree, Rob. A 10-year-old car is an old car, so I wonder how many people would change the battery if it costs $10,000 or more. I also wonder what effect the battery cost would have on resale value. Would I buy a used car that might need a $10,000 battery? I don't think so.

Rob Spiegel
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Blogger
Re: The batteries need to last
Rob Spiegel   4/16/2013 4:04:56 PM
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Good point Shehan. It will be interesting to see whether EV owners will replace worn-out batteries or whether they will turn to a new vehicle. With the high cost of batteries, I'm not sure we'll see a lot of new batteries dropped into 10-year-old cars.

MVRS
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Iron
Re: Can EV Batteries Last 20 Years?
MVRS   4/15/2013 2:50:01 PM
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As a person with an iPhone, I do not have the ability to easily change the lithium ion battery every year.  I am impressed with it heading toward 3 years now and no real change in operation time on a charge.  I was not expecting that.

Greg Stirling
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Platinum
Re: Can EV Batteries Last 20 Years?
Greg Stirling   4/15/2013 2:15:39 PM
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Shehan, Yes I presume it is much easier to market a car with '20 year batteries than '8 year batteries.  The 98 Jaguar, XJ8 has a Maintainence Free automatic 4 speed transmission.  I can see the blog "Maintainence Free Automatic Tranmission".  The tranmission has no dipstick to monitor fluid level and fluid integrity - one way to prevent a failure.  Are we to believe that this trans is going to run forever?  As a mechanical engineer, I dont think so.  GM says service their transmssions every 50,000 miles.  Turns out the Jag Tranny often fails between 50K and 100K and of course they cost 3 times as much as a GM transmission.  And now a car which sold for 55k is now worth $1100.  Why is it so expensive?  Because it is a Jaguar...

 

Francois Racicot
User Rank
Iron
Acceleration factor vs temperature
Francois Racicot   4/15/2013 12:19:19 PM
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When evaluating the life expectancy of a system, you normally use a range of conditions, for example three temperatures, three charge-discharge speeds, etc, from which one can calculate the acceleration factor for various fail conditions, and then estimate the reliability of the said system in real life, using assumptions for real life conditions.  When you use accelerated stress conditions, it is obvious that these are not real-life conditions: it would take 20 years to evaluate the life span of a battery!!!

Also, if it is true that cold weather is somehow good for battery life expectancy, it also adds a lot of stress to it, since you have to use more power for heating and defrosting.  Driving in snow will also drive a lot of power, as wipers, headlights, less efficient tires, wheel spinning on ice, higher resistance on snowy roads...  The regenerating braking systems may also work in a less efficient way if the ABS systems gets on (???). 

 

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