Sunday, October 7, 2012

Longevity Verses Safety

My Nissan LEAF has performed to every expectation I had conjured in my head during the long torturous 9 months I waited for delivery but there are still nagging questions about why certain things were done.  Now, in all finished products, there are several forces at work.  Engineering, Finance, and Sales.  Of the three, Finance usually has the most clout. they determine the pricing, so ultimately they determine what actually goes into the vehicle. Essentially they dictate the product and its up to Engineering to figure out how to build it and Sales figures out how to sell it.

So my question is the BMS (Battery Management System) and its lack of temperature controls and adequate monitoring equipment; namely the GOM (guess o meter, labeled as such due to its fluctuating estimate of your remaining range left which is based on recent driving performance. so go up a hill, your estimated range drops very fast or go down a hill and gain several miles of range estimate)

Last Summer I did some "hot weather" charging experiments (  to see what if any effect very warm weather had on the LEAF's ability to accept a charge. the premise was that when the LEAF battery pack detected very high temps, it would lower the amount of charge it would take to protect the pack. In my very small sample experiment, this premise seems to have been verified.

What did shock me was the lag time between the pack warming up and how long it took to cool down.  I knew the pack was sealed and began to wonder.

One thing that Nissan empathized was that the LEAF was totally safe.  They posted  videos on the pack being unscathed in  horrific crashes. We saw the LEAF drive back and forth thru a tank of water that was 3 feet deep and so on.  We saw the LEAF stuck by lightning and the pack weathered all tests without a hitch.

But now I think that going overboard on safety may have created a pack that is so insulated to the outside it has difficulty dissipating heat.  The pack warms up when charging and if add to that extreme ambient temps seen in the American Southwest, we may have a situation where internal pack temps could be at 120+º for days.

Phoenix went thru long periods where the overnight lows hovered near 90º.  Park it in the garage and leftover ambient heat radiating from the concrete pad would add a few degrees along with charging adding a few more and if it took greater than 24 hours to cool that off in normal temperatures? this could go a long way towards understanding why Phoenicians saw so much degradation so quickly

Now, a few people at MNL ( have investigated the possibility of  attaching a heat sink to the outside casing of the battery pack but that is complicated by the fact that Nissan covered the underside in plastic to reduce wind friction.

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