Date: Fri, 23 Dec 2005 23:29:08 -0800 (PST) From: [EMAIL PROTECTED] Subject: Re: [LIB] u100 battery life engineering problem
hi raymond first off I know about the high currect discharge pattern of li-poly, it is like a baby brother to the lead acid discharge. they are supposedly well suited for use in EVs. however they are not very good because they loose the rated capacity at lower currents <33 amps and if the ambient temperature is not around 70 degrees farenhient. they are a dead end in technology as near as I can tell. NiMH handle greater environmental temps better. for example, why use li in the libretto? if you go from 70 degrees to -10 you cut battery life in half from rated capacity. if you apply *any* external heat, even +-10 degrees the charge/discharge is so far off from the data sheet they are basically unapplicable. li has *always* had this problem which is why communication has *always* used NiCAD/NiMH!! If transcievers start being shipped with li I'll ship them back!! Transcievers are *not* office equipment they are used in every environment imaginable and are not used in environments where the ambient temp is constant in the least. you might ask why I mention transcievers. transcievers have a similar current use pattern to a laptop cpu board. high current coupled with stable *longer* *lower* current use. when you talk you use very high bursts of power than compared to when you recieve. the high voltage in the li doesn't matter since the li you describe can really only supply around .06 of a volt at 33 amps in the the real world not the data sheet. you see, voltage really doen't apply in the real world, it is simply a civilized method of describing a static discharge. it really doesn't exist. its like trying to describe the zero number. that doesn't exist either. that is the main reason li don't work though is that low voltage. lead acid, and some nimh are rated better and provide their actual discharge voltage in the data sheet. for some reason I don't know about li-ion/poly designers are misrating their cells. john > Date: Fri, 23 Dec 2005 09:08:37 +0800 > From: Raymond <[EMAIL PROTECTED]> > Subject: Re: [LIB] u100 battery life engineering problem > > 11.1V 2.2AH LiPoly batteries (3 cells) weighing about 120g can be readily > obtained that can pump 33 amps continuously without damage and without the > terminal voltage dropping significantly (internal resistance is in the > region of tens of milliohms per cell so we're talking drops of a volt or > two at 33 amps) ... and the pack itself is about 70x43x30mm in size. Any > decent hobby store will sell them to you (they're mainly used in electric > model planes, powered gliders and helis), in Australia you can get them > off-the-shelf for around $80-$90AUD. > > I dunno about you but as far as I'm aware there aren't any NiMH cells or > any other battery technology for that matter (at least none that are > readily available) that can be formed into a pack that can approach that > sort of weight, size or internal resistance for that voltage or energy > capacity. > > Besides, there has to be a reason why people from modellers to mobile > phone > makers to laptop and PDA makers switched to LiIon/LiPoly despite the more > complex charging/discharging safeguard circuitry involved. > > Which equations and graphed data do you refer to? > > - Raymond > > At 04:45 PM 22/12/2005 -0800, you wrote: >>Date: Thu, 22 Dec 2005 16:44:30 -0800 (PST) >>From: [EMAIL PROTECTED] >>Subject: Re: [LIB] u100 battery life engineering problem >> >>I've checked that out along with the equations and still don't get it. >>first off they're equations are questionable when run up against the >>graphed data. second when compared to the weight of the actual batteries >> I >>have to carry when using li-poly as compared to the actual weight of >> ni-mh >>cells the nimh cells are lighter. so what is this energy density stuff >>anyway? >> >> > Date: Thu, 22 Dec 2005 09:01:09 +1100 >> > From: Jonathan Paxman <[EMAIL PROTECTED]> >> > Subject: Re: [LIB] u100 battery life engineering problem >> > >> > On 22/12/05, [EMAIL PROTECTED] <[EMAIL PROTECTED]> >> wrote: >> > >> >> true, external temperatures affect li-poly but do not affect >> nicad/nimh >> >> chemistries unless they are in the +120/-20 range. gotta wonder why >> the >> >> industry uses an old technology like lithium when the nickel metal is >> so >> >> much more superiour in every way. >> > >> > Two words: energy density. >> > >> > Jon >> > >> > >> > >> > > > --- > > > /~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\ > | | "Does fuzzy logic tickle?" | > | ___ | "My HDD has no reverse. How do I backup?" | > | /__/ +-------------------------------------------| > | / \ a y b o t | [EMAIL PROTECTED] | > | | Need help? Visit #Windows98 on DALNet! | > | ICQ: 31756092 | www.raybot.net | > \~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~/ > > >
