On the contrary. Tesla cells discharge at a very LOW current. When you have 85kWh of battery, you only need 3.5C to make 300kW, and C/5 to cruise at 55MPH. Even the 120kW 'supercharger' tops out at about 2C (for the smaller 60kWh battery).
I would hazard this is why larger cells are not designed for large currents. RC cars are designed to run for 2 minutes and are trying to maximize power/weight. Most real world applications need more capacity and have to optimize energy/weight, so there's significantly less market for cells at 100Ah and 300C (not to mention that you would then have to find a way to manage 30,000 amps!!). -Ben On Jul 23, 2014, at 6:29 AM, George Tyler via EV <ev@lists.evdl.org> wrote: > I have been looking at this, seemed to me that for the capacity, smaller > batteries can discharge a higher current, I guess that's why Tesla uses 7000 > small cells? R/C batteries are often rated at 90C or even greater, I have > seen 300C. Look at this: > http://www.hobbyking.com/hobbyking/store/__51838__Turnigy_nano_tech_Ultimate > _6000mah_2S2P_90C_Hardcase_Lipo_Pack.html > 6 Ah and 90C gives 540 Amps! From a 2 Cell battery you can wrap your hand > around..... > > -----Original Message----- > From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of EVDL Administrator > via EV > Sent: Tuesday, 22 July 2014 8:21 p.m. > To: Electric Vehicle Discussion List > Subject: Re: [EVDL] How crazy am I? > > Another factor to consider is that while power capability varies by design, > as a general rule, smaller cells are usually capable of lower power output. > > For example, the CALB 40ah cells I mentioned are rated for a maximum > discharge of 2C (80 amps). At 144v, 80a is 11.5kW. Allowing for losses, > that's only about 12hp from your motor! > > Not being a lithium expert, I don't know how much more than this you can > actually draw before voltage sag really kicks in. But I'm pretty sure that > pushing them too hard will shorten their lives significantly. > > If you expect sporty, Mustang-y EV performance, but don't want to carry > around much of a battery, you'll need to find some cells designed for high > power. > > The 90ah Winstons I mentioned are rated for only 1C continuous, but they say > you can draw 10C for 10 seconds. It looks like you then need to allow at > least 50 seconds of either zero or much lower current for the cell to > recover (how often you can do this isn't clear from the spec). Other folks > here may know how realistic this is, and/or have some recommendations for > high power lithium cells. > > 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) > _______________________________________________ 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)
