My experience is that the Peukert Effect doesn’t come into play that much in normal driving with my 180Ah LiFePO4 cells in a light vehicle. If your battery capacity was such that normal discharge currents in your vehicle were 2C or higher I assume it would. Although I have discharge currents typically up to 2.5C during acceleration, and up to 1.4C going up hills, most of the time the currents are in the range 0.2C < I < 0.75C, and pack voltage under this load is within a few volts of the nominal 115V (3.2V/cell) all the way down to the 35% SoC, or higher, to which I normally discharge.
Because of the small change in voltage with SoC, and the result that each electron flowing out of the pack has about the same energy for most of my driving, Ah used gives a good indication of how far I can go on the Ah I have left. Because of that a Peukert setting of 1 has worked fine for my vehicle. On a 5% grade I use about 2.5x as much charge/mile as on level ground at the same speed, so I just mentally figure that in when estimating if I have the range to drive to a given point. I also know that coming down such a grade I will gain some energy with regen, so I just assume the care will not consume any energy coming down, to be conservative. Using energy would just complicate the estimates more since it requires use of another variable, pack voltage, and doesn’t add enough improvement in the accuracy of the estimate to make it worthwhile imo. The estimates of remaining range given by manufactured cars are also not very useful imo. For example, there is a 4500 ft change in elevation from a mtn pass here. I usually gain about 10Ah charge coming down, with pack V around 120V, so around 1200Wh. That is enough for my car to go about 6 1/2 miles on level ground at 50 mph. At E day, a guy with a Tesla S told me he gained 18 miles coming down the same drop. The S is of course much heavier than my car so gains more energy coming down, but also requires more energy/mile on level ground, so there is no way he gained that much range (which you can easily confirm by calculating the potential energy of the ~4700 lb vehicle at the top, using published info on the energy/mile required to move it on level ground at a given speed, and assume no more than 60% of that PE recouped to the pack, probably more like 50% due to the gradual descent). The estimated range is off because it is a moving average of historical energy/mile used, a large part of which is base on the last ~18 miles which were down hill. Of course my estimates of remaining range are more accurate because I know where I am going and what the terrain is like so I can take that into account in my estimate. If the S required you to enter your trip destination it could do similar by using something like google maps to determine elevation changes along the way, and give a more accurate estimate based on gps data on current location on the route. Without that info, past performance is no guarantee of future results, as they say in investing, and the 18 mile downhill illustrates. -- View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/Peukert-with-Lithium-Batteries-tp4669407p4669456.html Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com. _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
