is 47C too hot for HV?

Discussion in 'Gen 3 Prius Technical Discussion' started by Former Member 68813, May 27, 2014.

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  1. Former Member 68813

    Former Member 68813 Senior Member

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    Battery life being shorter with increased temps is a fairly common knowledge. This is why there is a temp management in the first place. Good source is this paper: http://www.ni-cd.net/accusphp/forum/docjoints/ID214_methode%20Nimh.pdf

    See figure 1. Battery life at 45C is half of that under 20C. The HV battery in my car spends most of the time between 30-40C (even when not driving), so I'm expected to get only 70% of the potential battery life.
     
    #21 Former Member 68813, May 31, 2014
    TomB985 likes this.
  2. Former Member 68813

    Former Member 68813 Senior Member

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    Unfortunately, that isn't correct. There is no uniformity of cell temps. Studies showed that the cells in the middle are hotter than the cells outside. Probably because the battery case serves as a heat sink. That contributes to lower capacity of middle cells in used HV batteries.
    Here is some good evidence for older gen prius, but still relevant IMHO:
    http://www.nrel.gov/vehiclesandfuels/energystorage/pdfs/2a_2002_01_1962.pdf
    http://researchcommons.waikato.ac.nz/bitstream/handle/10289/5714/PriusBatteryRebuildability-LeijenScott2011.pdf?sequence=1
     
    #22 Former Member 68813, May 31, 2014
  3. GasperG

    GasperG Senior Member

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    I wonder what battery temperature is getting PiP or li-ion Prius+? I suppose the internal heat up is lower as li-ion is more efficient, but ambient temperature and sun can easily shot it over 40° C with not adequate air cooling. Do we have data for Toyota's li-ions?
     
    #23 GasperG, Jun 2, 2014
  4. TomB985

    TomB985 Member

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    That's good info, thanks for sharing. But I question it's accuracy.

    Just yesterday I got my Torque app setup on my car, and I started tracking battery temps and cooling fan performance. On the 14-mile trip to the hospital with my wife the temp sensor I was monitoring achieved a peak of 95 degrees Fahrenheit. The cabin temp was 72, yet the cooling fan never activated until it hit 95. And at that point it was on the lowest setting.

    If cycle life truly started decreasing at 68 degrees wouldn't the fan have been on the entire time? Why would the engineers let it get that hot before even beginning to cool the battery? I have a really hard time believing that any of us know something that they don't after fifteen years in production, and even my engineering challenged brain can deduce that running the fan would have kept temps lower than with the fan off.

    So what am I missing here?
     
    #24 TomB985, Jun 2, 2014
  5. Former Member 68813

    Former Member 68813 Senior Member

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    Again, you are missing the compromise. Higher battery temp = higher performance (power) but shorter life.
     
    #25 Former Member 68813, Jun 3, 2014
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