[Oeva-list] Leaf battery

Dan Hammerstrom strom at cecs.pdx.edu
Mon May 2 15:32:23 PDT 2011


As someone mentioned, it is probably not Peukert with Li-Ion batteries.  All batteries have some internal resistance.  Although just a few ohms for a large pack, if you get enough current going (in or out) you get a pretty good voltage drop across that resistance, which results in a energy loss (as heat).  There is then even less voltage to drive the motor, so the draw gets increased even further.  Add to that increased rolling resistance and aerodynamic drag (which increase as the square of the speed).

So depending on the speed you are driving, that is, how much current you are drawing, your batteries will be significantly less efficient.

Also, it is not clear if the Leaf SOC estimation factors battery resistance into it's calculations.  Most BMS systems do not, since measuring and updating resistance measurements is complex.  However, the Leaf represents some pretty sophisticated engineering and may very well do so.

-- Dan




On Apr 29, 2011, at 6:20 PM, Alan Batie wrote:
> I've been looking at the Carwings data for that trip to Portland a couple weeks ago, and either the estimator is being awfully conservative (which would make sense except for the reports of people running out of juice early), or the energy consumption sensor/calculation Carwings is using is faulty, or the battery is smaller than they say:
> 
> Battery spec: 24kwh
> 
> Carwings report for the return from McMinnville (where it got a 100% charge that Sunday): 11.7kWh 48.6miles 4.2miles/kWh
> 
> Range estimator/battery gauge: 66% (27 miles remaining)
> 
> kwh capacity derived from usage: 11.7/.66 = ~18kwh
> 
> The 66% is consistent with 27 miles remaining after going 48 miles.
> 
> I'm guessing Peukert at work...
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