Agreed. So, that's where the 24% number came from - your third method. I was trying to fit it into one of the first two methods, and it didn't make sense. Peri
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of tomw Sent: 20 March, 2014 7:55 AM To: [email protected] Subject: Re: [EVDL] How can regen be a reason to buy or not? : EVLN:Fiat500eEV> close to perfect Peri, There are a number of different ways to state the amount of regen you get. One is expressing as the ratio of energy gained through regen on a trip to the total energy used on the trip. So for example if I measure a total of 1 kWh on energy back into the batteries on a trip, and a total of 12 kWh out of the battery on that trip, then regen was 1/12 = 8.3%. I'm saying that I expect this measure of efficiency to be in the range 3% to 25% for most driving. I have not done a test where I drive slowly, say 30 mph, with repeated stops and on hills to see what value I get for this measure. Another is looking at how much of the kinetic energy (mv^2/2) of the vehicle is typically regained when you stop for say a traffic signal. I've measured that a few times at about 50%, by data logging battery current and voltage at a sample rate of 1 sample per second. The calculations I posted generally agree with that. I also have used one other measure...the ratio of the energy gained through regen going down a hill to the energy used going up the hill. This ratio was 24% on the hill in the graph to which I gave a link. The data also shows that the energy used per mile going up that about 5% grade was 2.5 times larger than the average energy/mile used on the overall trip. The efficiency of an AC motor mainly depends on the slip (in fact, the Curtis "spyglass" gauge that comes with HPEVS motors/Curtis controllers has an LED that lights up based on the slip to indicate 3 different levels of efficiency). You can have good efficiency at fairly high power if the motor rpm is high and the torque is moderate so that slip is a few percent or so, since power is the product of torque and shaft angular velocity. So efficiency vs rpm curves for motors usually have a fairly broad region where the efficiency is around 90%. Efficiency is lower during hard acceleration though, so I assumed around 85% for the motor and 95% for the controller (Rhinehart states 97% efficiency for their inverter), so about 80% combined. Might be as low as 70% during the first part of acceleration I would guess. The LED on the "spyglass" changes from red (high slip, low efficiency), to yellow to green (low slip, high efficiency) fairly quickly if I "floor" it, indicating slip and inefficiency are only larger for a brief time. In real driving you of course many times accelerate at a different rate than you decelerate, and you don't drive at the same constant speed in between stops/starts. I just made those assumptions to simplify the equations. I could include these refinements as well as grade, but I think the simpler equation captures most of the behavior, and the refinement would not give very different results. -- View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/EVLN-Fiat-500e- EV-close-to-perfect-tp4668392p4668582.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) _______________________________________________ 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)
