Thanks Lee, that is neat to know. I freely admit having little understanding of lead acid.
On Sat, Jun 20, 2015 at 1:15 PM, Lee Hart via EV <ev@lists.evdl.org> wrote: > Michael Ross via EV wrote: > >> I think it is very valuable knowing that a Li ion cell can hold its charge >> indefinitely. Particularly compared to the incumbent competitor - lead >> acid cells. There is a least an implication that the the loses may be of >> no consequence after design and manufacturing improvements. There is no >> possibility of achieving this ever with lead acid. >> > > Surprisingly, that's not entirely the case. > > The self-discharge rate of a battery is usually traded off with many other > parameters; capacity, life, peak current, etc. For most lead-acid > batteries, the market considers factors other than self-discharge to be a > *lot* more important. > > But, there are exceptions. I just pulled some Gates "Cyclon" spiral-wound > lead-acid gel cell off the shelf. They were purchased in Nov 1994, and used > for 5 years in electric lawn mower. My notes say the last time they were > charged was on Nov 14, 2000. At that time, they still had about 1.5ah of > capacity (out of their original 2.5ah). Today, 4 out of 13 *still* have > charge in them (1.9v or more open circuit). > > One reason for this is that Gates used *pure* virgin lead; not a lead > alloy. Almost all other lead-acid batteries alloy the lead with antimony, > calcium, cobalt, or just the random mix of junk left over in scrap lead. > Or, someone will have watered the battery with tap water, which adds its > own unknown impurities. All this "stuff" worsens the self-discharge > characteristics. But that doesn't matter to most customers; they will be > recharging the battery often enough so it never runs dead. > > If you care, Gates was bought out by GE, who sold out to Hawker, who is > now owned by Enersys. So you can still buy these Cyclons today! But they > have an insignificant market, because (almost) no one cares about > self-discharge. > > On Fri, Jun 19, 2015 at 8:11 PM, Cor van de Water via EV< >> ev@lists.evdl.org> >> wrote: >> >> David, >>> >>> Why do all manufacturers of Li-Ion batteries specify the amount of >>> self-discharge >>> and why do people like me who monitor Li-Ion batteries over time, see and >>> measure >>> the self-discharge? >>> I understand that you say "theoretical" the pure Li-Ion cell may not >>> have a >>> self discharge mechanism and thus the actual present self-discharge >>> appears to be >>> a spurious effect, possibly caused by contamination, so the amount of >>> self-discharge >>> is a quality indicator of the (lack of) contamination in the cell... >>> >>> However, saying that the ideal (theoretical) cell does not have any >>> self-discharge is as valuable >>> as saying that the ideal (theoretical) connection does not have any >>> resistance. >>> In practice however you better take that resistance into account when >>> sizing your wiring and connections. >>> Similar to taking self-discharge (and especially the difference in >>> self-discharge between cells) into account >>> when designing a battery pack. >>> >>> Cor van de Water >>> Chief Scientist >>> Proxim Wireless >>> >>> office +1 408 383 7626 Skype: cor_van_de_water >>> XoIP +31 87 784 1130 private: cvandewater.info >>> www.proxim.com >>> >>> >>> This email message (including any attachments) contains confidential and >>> proprietary information of Proxim Wireless Corporation. If you received >>> this message in error, please delete it and notify the sender. Any >>> unauthorized use, disclosure, distribution, or copying of any part of >>> this >>> message is prohibited. >>> >>> >>> -----Original Message----- >>> From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of David Nelson >>> via >>> EV >>> Sent: Friday, June 19, 2015 4:37 PM >>> To: Bill Dube; Electric Vehicle Discussion List >>> Subject: Re: [EVDL] "Zero self-discharge" (was: Bicycle battery) >>> >>> Bill, >>> >>> I have dug through many scientific papers on Li batteries and how they >>> work and I haven't been able to find anything about a theoretical >>> self-discharge mechanism. I have found some explicitly talking about the >>> lack of a charge shuttle mechanism like in lead-acid batteries, however. >>> >>> One paper I read has a section devoted to figuring out a charge shuttle >>> mechanism to add to a Li cell. It isn't a paper for the faint of heart, >>> however. It is "Nonaqueous Liquid Electrolytes for Lithium-Based >>> Rechargeable Batteries" by Kang Xu published in the Chemical Review, >>> 2004, >>> Vol. 104, No. 10, pp. 4303-4417 and published on the web 09/16/2004. >>> >>> While I'm sure I don't get it 100% of the time I try to make sure I say, >>> "LiFePO4 cells have no theoretical self discharge mechanism." >>> This, according to all I have been able to find on the cells, is true. >>> Also, the most ardent anti-BMS people I have found have in fact done a >>> lot >>> of searching of the scientific literature and came to the same >>> conclusion. >>> It was not just something they made up to support their anti-BMS >>> position. >>> >>> If you have other literature showing what the self-discharge mechanism is >>> please share it. >>> >>> On Fri, Jun 19, 2015 at 11:46 AM, Bill Dube via EV<ev@lists.evdl.org> >>> wrote: >>> >>>> This "zero self-discharge" myth seems to be a common thread with the >>>> "anti-BMS" crowd. I don't know where this misinformation comes from. >>>> >>>> All cells have self-discharge. It is just a matter of degree. >>>> Also, the self-discharge varies from cell to cell. That's why you need a >>>> >>> BMS. >>> >>>> These are well-documented facts for all those that care to >>>> investigate, either through the scientific literature or by simply >>>> systematically testing cells for themselves (as Lee Hart has done.) >>>> >>>> I strongly suspect the "zero self-discharge" myth comes from >>>> the same unscientific source that the anti-BMS myth has sprung from. >>>> >>>> Bill D. >>>> >>>> _______________________________________________ >>>> 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) >>>> >>>> >>> >>> >>> -- >>> David D. Nelson >>> >> > > -- > The greatest pleasure in life is to create something that wasn't > there before. -- Roy Spence > -- > Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com > _______________________________________________ > 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) > > -- 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) 585-6737 Land (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google Phone (919) 631-1451 Cell michael.e.r...@gmail.com <michael.e.r...@gmail.com> -------------- next part -------------- An HTML attachment was scrubbed... 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