SageBrush wrote: ↑Sat May 07, 2022 5:19 pm
GRA wrote: ↑Sat May 07, 2022 3:48 pm
C-rate is dependent on what individual cells can handle in terms of voltage and current, and is useful for comparing packs of similar voltage and chemistry. For a given chemistry, string more cells together in series and you don't have to put more current through them.
Put more cells in series, and notice what happens to the pack internal resistance.
I'm sorry, but you don't know what you are talking about.
Sure, resistance increases, but since the cell limit is determined by max. voltage and current it's far easier to boost the rate of charge (or discharge) power by putting more cells in series. Which is why more and more companies, including Tesla, are opting for pack voltages well over 400V so they can charge faster, despite your previous adamant declarations that it made no sense to do so.
BTW, re pack pre-conditioning to maximize charging speeds, while I'm all in favor of it for edge cases I wonder just how much of an advantage this would amount to in the real world. Most people take extended road trips in summer, when the pack would normally be warm, and even if it doesn't start that way doing a FC repeatedly every two hours as is currently required by almost all BEVs with a nominal range of 250-300 miles would probably heat the pack up to where you'd want it. I look forward to some extended range road tests of the Ioniq 5/EV6 that involve repeated FCs, in both cool and warm temps.
Of course, for those longer trips in cooler weather, pre-conditioning should help. I once drove from Oakland to Flagstaff (slept there), then on to Albuquerque and up to Taos Ski Village (slept), then to Boulder and Rocky Mtn. N.P. (slept), Old Snowmass and on to Arches N.P. (slept), Zion and on to near Lone Pine (slept), then back to Oakland via Tioga Pass in October. I remember we got snowed on crossing either Tennessee of maybe it was Fremont pass (don't remember which highway we took) in Colorado from I-70 on the way to Leadville. OTOH, given the steep climbs and descents and/or sustained high speeds on that trip, I'm sure any pack would have been plenty warm from providing power/accepting regen.