Yes, I follow you David. Thanks for putting in that perspective - 30Wh isn't very much energy - enough to power a 100w bulb for about 20 minutes..
Conclusion for me: saving brakes and getting potentially 20% more range in city driving is worth it. If I lived outside Chicago, that might be a different matter. Peri -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of David Nelson Sent: 19 March, 2014 5:00 PM To: Electric Vehicle Discussion List Subject: Re: [EVDL] How can regen be a reason to buy or not? : EVLN:Fiat500eEV> close to perfect On Wed, Mar 19, 2014 at 4:17 PM, EVDL Administrator <[email protected]> wrote: >> One more note: the drive train efficiency shouldn't be counted when >> computing the effect of regen to extend range. > > Quite the opposite! You expend energy on friction and windage losses when > accelerating AND when decelerating. Thus when computing the efficiency of > regen, you have to count those losses TWICE. Actually, what Peri is saying is true. Since he/we know how much energy is expended by the battery to move the vehicle a certain distance now, and that includes all the frictional losses, it is sufficient to know how much energy the battery was able to absorb from regen to calculate how much the range is extended without needing to know the efficiency values. Peri, maybe this will help. When a vehicle is stopped by any means the only energy which has to be extracted from the vehicle to bring it to a stop is its kinetic energy assuming a level surface. You said that you had a 2011 Nissan LEAF. Wikipedia lists the mass as 1,521kg and you were wondering about regen from a speed of 30mph. Since SI units are much easier to work with for such calculations convert 30mph to 13.4m/s. KE = 1/2 mv^2 so the kinetic energy of a LEAF traveling 30mph is KE = 1/2(1521kg)(13.4 m/s)^2 = 136,555 kg*m^2/s^2 = 136,555 J. Since 1 Joule = 2.7778*10^-4 Wh we have only 37.9Wh of Kinetic energy which could be recouped by regen. If your system was 100% efficient when using regen how far could you drive on that 37.9Wh of energy? If only 80% of the energy went back into the battery that leaves 30.3Wh. I don't know what the LEAF consumes driving 30mph but lets assume it can go 5 mi/kWh which means 200Wh/mi. This translates to additional range of 0.152 miles or about 800 feet at a steady 30mph. That is likely a very optimistic number, however. As others have pointed out, regen is typically a very small part of a drive. In my Gizmo I have a SepEx motor setup and I see a 3-4% improvement using regen based on the Ah gained by the battery as measured by a CycleAnalyst. I want to save brakes more than energy in my case so I have regen stay active as long as possible so by the time it drops out it is pulling more out of the battery than regen can create so I see a loss of battery energy below about 10mph or so. I'm sure the AC setup is way more efficient than my system. -- David D. Nelson http://evalbum.com/1328 http://www.levforum.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)
