We are really letting the smoke out on this one. The definition of the units for energy and capacity are instructive (though still smokey)
Energy is counted in Joules - energy, work and heat are trickily the same. Joule = Newton meter = Watt second = Coulomb Volt Coulomb is the basic unit of electrical charge. the charge of 6.241 x 10^18 electrons. Its SI definition is the charge transported by a constant current of one ampere <http://en.wikipedia.org/wiki/Ampere> in one second<http://en.wikipedia.org/wiki/Second> . So that circles around to what Davis is saying - you cannot talk about energy in terms of coulombs without talking about the voltage also. Therefore capacity, which is how much charge is accumulated, is different from energy which is this much charge accumulated at a different potential than some other proximate group of charges. Every system tries to run downhill to a state of lower system potential. In a capacitor (don't you just love that name - a thing that has capacity) of two plates you can pile up more charges on one side to create a potential difference, or you can rearrange them differently in the system - like take an uncharged cap and pull all the charges off one plate onto the other. It takes energy to do that. The capacity is how many charges you can make hang around on a plate. The energy is what you use (or work, or heat, or power over time) to put them temporarily at a higher potential all on one plate. You do work to create that potential and you can harvest it: You connect the two plates with a wire, the charges can now flow freely to equilibrate the system, and in the meantime you can convert that flow into some heat, work (in a motor), and so on. In a sense a battery is a fancy capacitor. I never heard the term State of Energy before this discussion. I can intuit State of Capacity. I guess we ignore the fact that a 3.2V nominal battery and a 3.4V nominal battery that have the same capacity are not the same in term of potential to store energy or work. Aha - this is why they say LiFePO4 are less energy dense! Am I right? It is really that they operate at a lower voltage. You can move the same number of charges in an LFP and there is a limit that is lower than say a LiNiMnC I hear power density discussed...some chemistries have more or less of this.... Power has a time component so maybe power density has to do with how fast you can get the work done with a battery? Probably a structural issue more so than a chemistry issue? I have my doubts that is useful for anyone else, but it made it clearer for me having to write it out. On Thu, May 8, 2014 at 10:19 PM, Jan Steinman via EV <[email protected]>wrote: > On 2014-05-08, at 19:11, David Nelson wrote: > > > On Thu, May 8, 2014 at 5:22 PM, Jan Steinman via EV <[email protected]> > wrote: > >> On 2014-05-08, at 17:01, David Nelson wrote: > >> > >> Seems a bit pedantic to me, but no worries. > >> > > Maybe it is just a disconnect between how a > > physicist sees things and an engineer sees them. > > Don't get me started on my collection of "physicist versus engineer" > jokes. :-) > > :::: A summer vacationer stopped past the other day and said, "If I could > find a farm like this, which just runs itself, I'd be tempted to buy." I > had to tell him to resist the temptation if that was the awy he felt. No > farm runs itself, even though it may seem to in midsummer... But the land > doesn't "just run itself." If we left it to itself, the pastures would be > overrun by birch and sumac, the fences would rot and rust, and we would > soon be living in a tumble-down house crowded by a thicket. -- Hal Borland > :::: Jan Steinman, EcoReality Co-op :::: > > _______________________________________________ > 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) > > -- Put this question to yourself: should I use everyone else to attain happiness, or should I help others gain happiness? *Dalai Lama * Tell me what it is you plan to do With your one wild and precious life? Mary Oliver, "The summer day." To invent, you need a good imagination and a pile of junk. Thomas A. Edison<http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html> A public-opinion poll is no substitute for thought. *Warren Buffet* Michael E. Ross (919) 550-2430 Land (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google Phone (919) 631-1451 Cell (919) 513-0418 Desk [email protected] <[email protected]> -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140508/e0601fdf/attachment.htm> _______________________________________________ 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)
