Yes, I agree - it depends on the "duty cycle" of regen compared to maintaining constant, level speed. More accurately, the duty cycle should only include the time regen is active. Thus, if you spend 20% accel & decel and, for sake of discussion that's 50% of the time each, you have only 10% time in actual regen mode.
For my part, I need to pay more attention to that ratio. With a lot of hills and stop signs, I'm thinking it is close to 25% time in regen mode - which (with 80% efficiency) is a theoretical 20% range extension. Well, maybe that 20% figure put out earlier is pretty reasonable :) Peri -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Peter Gabrielsson Sent: 19 March, 2014 3:06 PM To: Electric Vehicle Discussion List Subject: Re: [EVDL] How can regen be a reason to buy or not? : EVLN:Fiat500eEV> close to perfect You're comparing a hypothetical case against peoples real world reported numbers under real world conditions. The power is also only half the equation, energy is what matters. If you spend 100s driving at 5kW and 20s accelerating and decelerating at 25kW you're still only gaining 33% on a 100% efficient regen system (500kWs with regen vs 750kWs without). I recall someone posting a test where they had accelerated from standstill to 60 and back down to 0, I think in a Tesla or a Leaf. The regen efficiency was pretty high, 60-70% of the energy was recaptured IIRC. So if you drive like that all the time your range will be 60-70% better with regen than without. It would still be less efficient than driving at a constant speed of 30mph. On Wed, Mar 19, 2014 at 2:26 PM, Peri Hartman <[email protected]> wrote: > To be a little more specific, suppose you have a "slippery" car, like the > Leaf. I roughly computed that to maintain 30mph on a flat road should take > around 5Kw, maybe less. > > If you spend most of your time driving up and down hills where you have to > brake, short distances between stops where you have to brake, and stay > under > 30mph, then 5Kw becomes almost negligible (observing my gagues, it takes > around 20 - 30Kw to accelerate on the level without holding up traffic). > Thus, with regen, you should get somewhere close to 80% more range than > without regen. > > One more note: the drive train efficiency shouldn't be counted when > computing the effect of regen to extend range. The same losses apply > whether the energy comes from the original charge or from regen, thus the > percentage is based solely on what percent of energy is recaptured from > regen. > > Peri > > -----Original Message----- > From: Peri Hartman [mailto:[email protected]] > Sent: 19 March, 2014 2:11 PM > To: 'Electric Vehicle Discussion List' > Subject: RE: [EVDL] How can regen be a reason to buy or not? : > EVLN:Fiat500eEV> close to perfect > > Which number? 65-75%: 80% regen efficiency * 80% drive train efficiency = > 64%. Cor hypothesized up to 72%. > > 20%: several people mentioned a hypothetical 20%; don't remember who > without > looking. > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf > Of Peter Gabrielsson > Sent: 19 March, 2014 2:05 PM > To: Electric Vehicle Discussion List > Subject: Re: [EVDL] How can regen be a reason to buy or not? : > EVLN:Fiat500eEV> close to perfect > > And how do you come up with that number? > > > On Wed, Mar 19, 2014 at 2:03 PM, Peri Hartman <[email protected]> wrote: > > > Yes, I completely realize that the effectiveness of regen, and range in > > general, depend on many factors. Yet, in theory one should be able to > > achieve 65-75% effective range improvement. I'm only seeing people > report > > numbers up to 20%. That's a huge spread. Has no one actually run a > > circuit > > where they could show a 70% improvement? > > > > Peri > > > > -----Original Message----- > > From: [email protected] [mailto:[email protected]] On > > Behalf > > Of Cor van de Water > > Sent: 19 March, 2014 1:16 PM > > To: Electric Vehicle Discussion List > > Subject: Re: [EVDL] How can regen be a reason to buy or not? : > > EVLN:Fiat500eEV> close to perfect > > > > Peri, > > It depends on the road and driver. > > If you take a long trip with essentially no stops and no downhill or > > other regen opportunities, then the only time regen might kick in is > > when you stop at your destination. At that time the regen might be just > > a single percent of energy recovered and your range is not extended at > > all. > > > > If you drive through a city with a stop-intersection every single block, > > then you have lots of regen opportunities and the value is likely more > > in the 20-30% range extension. > > > > Some guys on this list know that they should never charge their EV more > > that for example 50% full at home, because they have a looooooong > > downhill into town and they do not want to reach the 80% mark before > > getting into town, since regen starts to cut out by then. Definitely 30% > > or more range extension... > > YMMV... > > > > 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 Peri Hartman > > Sent: Wednesday, March 19, 2014 12:57 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 > > > > I'm sorry for not being clear. The number I really want is how much it > > extends your range. That can be deduced by knowing how much energy is > > recovered by regen and then calculating the range extension based on > > that > > plus all the losses due to rolling, wind, etc. > > > > I do see figures like 5 to 20%. However, if speeds are limited to be > > under > > 30mph and regen is "stiff" enough to avoid mechanical braking, I would > > expect a much higher number than 20%. What am I missing? Has no one > > tested > > this? Or are the other (non regen) losses that high? > > > > Peri > > > > -----Original Message----- > > From: [email protected] [mailto:[email protected]] On > > Behalf > > Of EVDL Administrator > > Sent: 19 March, 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. 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