Note that the electric drivetrain (including regen) does not have a single efficiency, since the losses tend to increase with power. So, both acceleration and (regen) deceleration will have a certain efficiency at full power and a much higher efficiency at reduced power. For example, a motor may be 85% efficient at a certain max power level. the drivetrain (gearbox, diff, bearings, brake drag) may eat up another 10% and the inverter may be as good as 95% efficient, then the internal resistance of the batteries will again throw in a loss of 10% at max power and you have a total efficiency of: 90%(batt) x 95%(controller) x 85%(motor) x 90%(drivetrain) = 65% That means that of 1 kWh of energy stored (charged) into the battery, only 650 Wh makes it to the wheels in the form of acceleration under max power. But at half power, the losses may be less than half those at max power, so you may see 85% efficiency at half power... During regen, the same thing hold for the reverse path: brake at max power (fastest deceleration) and yo umay only recapture 650Wh in the battery from 1kWh in Kinetic energy. So, if you have a certain speed, then regen-brake at max power and then re-use that energy stored in the battery at max acceleration again, you go through the drive-train losses twice, so you are able to put the to wheels: 65% x 65% = 42% of the original Kinetic energy of the moving vehicle. Better than nothing, but less than half the original energy is available after this worst-case stop and start. Now, if you use half power for regen and acceleration, your efficiency may be as good as 85% x 85% = 72% which means that almost three quarts of the original energy can be re-applied to accelerate the vehicle again if you can avoid lead foot driving and use only half the max power... Of course, for each vehicle these numbers will be different - I just used what I had in my head for an old-skool DC drive and saggy flooded batteries, which is not the typical regen-setup but it illustrates the process nicely.
Hope this clarifies, Cor van de Water Chief Scientist Proxim Wireless Corporation http://www.proxim.com Email: [email protected] Private: http://www.cvandewater.info Skype: cor_van_de_water Tel: +1 408 383 7626 -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of EVDL Administrator Sent: Wednesday, March 19, 2014 12:39 PM To: Electric Vehicle Discussion List Subject: Re: [EVDL] How can regen be a reason to buy or not? : EVLN: Fiat500e EV> close to perfect On 19 Mar 2014 at 9:29, Peri Hartman wrote: > I don't think my question has been answered: what is the actual > effective efficiency of regen when driving in the city with lots of > hills, lots of stop and go, and speeds under 30mph? Are you asking about the efficiency of regen itself? With software controlled inverters and AC motors, I would think that if the drive system is, say, 80% efficient during motoring, it should be close to that when regenerating. If you're asking how much of the vehicle's kinetic energy is recovered by regen, that might be judged by how much it extends range. I've read that the range extension of regen varies from 5% to 20% depending on terrain and driving style. Lots of use of stop-and-go (slowing down without using the friction brakes), and/or lots of hills will tend to push it toward the higher number. David Roden - Akron, Ohio, USA EVDL Administrator = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Note: mail sent to "evpost" and "etpost" addresses will not reach me. To send a private message, please obtain my email address from the webpage http://www.evdl.org/help/ . = = = = = = = = = = = = = = = = = = = = = = = = = = = = = _______________________________________________ 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)
