I have *measurement data* as well as experience in old "Classic" Prius braking and that shows a power of 50 Amps at 320 Volts or 16kW into the old style battery. Assuming a 80% efficiency of the motor and maybe 85% for the inverter, the braking power at the wheels is probably around 24kW from just the electric regeneration into that small pack and it might not even be a pack limit, since motor and inverter are also part of the equasion and limited to around that power level. Certainly a pack can take a high peak charge, just like it can deliver a peak discharge as long as it is comfortable within its operational limits. I had an electric truck with an AC drivetrain and since the motor was driven by a 3-phase inverter, it could absorb the same current as it could deliver, so it could actually brake harder than accelerate (because the pack voltage is higher during charging). I experimented with that inverter configuration and one day I set it to start regen even when the pack was not drawn down enough. So, sure enough on my regular commute I had someone cut in front of me just after I merged on the freeway only 2-3 miles from home, so I hit the brakes and the pack voltage went from close to its nominal 312V (26 lead acid batteries) to over 420V at which point the inverter protected the other electronics that had a max voltage limit of 425V, by doing an emergency shutdown, so I had to coast to a stop on the shoulder and reboot my EV (and later reconfigure the inverter to avoid that behavior by not allowing regen until 10% pack usage) At other times I noticed that this truck could almost crunch up its driveshaft from the large power being regenerated back into the pack until pretty low RPMs. (200A at around 350V, so over 100kW at the wheels).
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 Willie2 Sent: Thursday, November 14, 2013 7:42 AM To: Electric Vehicle Discussion List Subject: Re: [EVDL] EVLN: Graphene Supercapacitors Ready For EVs On 11/13/2013 11:25 AM, EVDL Administrator wrote: > On 13 Nov 2013 at 3:33, brucedp5 wrote: > >> Conventional batteries take so long to charge that they cannot efficiently >> store braking energy. > Hold on there! A lead-acid battery can be charged at thousands of amps if > it's below 80% SOC. > > To view it from another angle, a battery can usually charge as fast as it > can discharge. I'm sure there are exceptions, but in my experience, most > drivers seldom decelerate dramatically faster than they accelerate. > > That said, supercaps have been shown to be useful in mitigating peak > currents on discharging, and maybe this would help too on charging. But I > suspect that further battery refinement - and the extra cost of the caps - > will make this a moot point. I also noticed the poor quality of the article also and intended to comment on it at the time. I guess he is thinking of not BEVs but hybrids with relatively small batteries. As far as I know, ALL BEVs with regen capture an acceptable amount of braking energy. A Tesla S (warm with a not full battery) can regen at 60kw; that covers probably more than 90% of braking needs. I have no personal experience, but I suspect even the small battery in a Volt allows an acceptable job of regen. > _______________________________________________ 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)
