---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Mon 01/05/15: 4 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 08:08 AM - Re: lithium facts (davevon) 2. 10:30 AM - Re: Re: lithium facts (Rick Beebe) 3. 03:46 PM - Re: Re: lithium facts (Robert L. Nuckolls, III) 4. 10:40 PM - Re: Overvoltage crowbar availability? (Justin Jones) ________________________________ Message 1 _____________________________________ Time: 08:08:32 AM PST US Subject: AeroElectric-List: Re: lithium facts From: "davevon" Hi All, Hope I'm not too late to join in on the discussion, I wish I would have seen this sooner. Greg over at B&C pointed me in this direction. I'm in process of redoing the complete electrical system in a Laser 230 aerobatic airplane. The system had evolved into something that was very heavy, unsafe and just plain wrong in so many ways... To save weight I bought an Aerovoltz/Ballistic LiFePo4 EVO2-16 battery. I'm using a B&C SD-8 with their external regulator and OV protection. Researching charging voltages for the LiFePo4 chemistry I'm finding a large variation in recommendations. The EV (Electric Vehicle) guys claim 3.33v/cell is 100% charged and shouldn't be taken beyond that. http://www.diyelectriccar.com/forums/showthread.php/you-all-destroying-your-lifepo4-cells-65336.html Then I've seen a couple of places saying 3.65v/cell is 100% charged with a max voltage of 4.2v. http://www.powerstream.com/LLLF.htm The stock B&C system charges at 14.4v and the OV protection is set 16v. Ballistic batteries is telling me to charge at 14.4v but don't go over or "bad things will happen". I'm sure that the OV protection has to be set more than even a .1v higher that the regulated voltage to prevent nuance trips. I'm guessing that there's some variation between cell manufactures and their voltage specs and add to that the battery manufactures/assemblers add their safety margin which leads to a case like the Aerovoltz/Ballistic having no leeway between the charging voltage and do not go over voltage... So is there a definitive answer??? Thank you for your time, Dave Read this topic online here: http://forums.matronics.com/viewtopic.php?p=436650#436650 ________________________________ Message 2 _____________________________________ Time: 10:30:04 AM PST US From: Rick Beebe Subject: Re: AeroElectric-List: Re: lithium facts On 01/05/2015 11:07 AM, davevon wrote: > > > [...] > Researching charging voltages for the LiFePo4 chemistry I'm finding a > large variation in recommendations. > > The EV (Electric Vehicle) guys claim 3.33v/cell is 100% charged and > shouldn't be taken beyond that. > > Then I've seen a couple of places saying 3.65v/cell is 100% charged > with a max voltage of 4.2v. I have an EV that I converted with LiFePo4 cells. While charging I charge until the voltage hits 3.5v per cell (and I've heard that 3.65 is the highest safe range but there's little added beyond 3.5v). I then hold the voltage until the current drops to 0.05C. After I stop charging the voltage will drop to somewhere around 3.2-3.3v. So maybe that's what the first voltage is about. > The stock B&C system charges at 14.4v and the OV protection is set > 16v. Ballistic batteries is telling me to charge at 14.4v but don't > go over or "bad things will happen". I'm sure that the OV protection > has to be set more than even a .1v higher that the regulated voltage > to prevent nuance trips. Since they're building batteries to replace lead-acid cells, its pretty silly of them not to protect their batteries from "normal" lead-acid voltages. If they have 4 cells, 14.4v is 3.6 per cell which should be fine. The maximum of 4.2 x 4 = 16.8 so bad things shouldn't happen with an occasional foray above 14.4 except perhaps shortening the life of the battery. > I'm guessing that there's some variation between cell manufactures > and their voltage specs and add to that the battery > manufactures/assemblers add their safety margin which leads to a case > like the Aerovoltz/Ballistic having no leeway between the charging > voltage and do not go over voltage... > > So is there a definitive answer??? I've found that there's quite a variation in knowledge about LiFePo4 cells among the people who are selling them and even among those building them. --Rick ________________________________ Message 3 _____________________________________ Time: 03:46:34 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: lithium facts >>So is there a definitive answer??? > >I've found that there's quite a variation in knowledge about LiFePo4 >cells among the people who are selling them and even among those building them. Gee . . . what was your first clue? I've been sifting the lithium pile of sand for about 4 months. I'll be writing an article for KitPlanes on some of my findings. In brief, I believe I am on solid ground with the following assertions: LiFePo4 IS the chemistry of choice The MAX charge voltage for LiFePo4 is 4.2 volts per cell. Sift through the spec sheets for commercial offerings of LiFePo4 and you'll find MOST cells "rated" at 3.7V charge, 3.3V nominal delivery point. Here are some exemplar performance curves one particular cell Emacs! Note that charging at 4.2 volts nearly DOUBLES the cell's contained energy. Stack 4 cells in series to perform in a 14v system and you would have to charge the battery at 16.8 volts. A tad high for many 14V bus operated devices . . . and perhaps out of reach for many voltage regulators. It's a little different ball game for consumer products that discharge lithium cells with switchmode power supplies. You can order chargers rated for EITHER 3.7 or 4.2 volts per cell. There are no caveats offered for the use of these chargers with any of the COTS lithium products . . .hence, no big risk . . . but a substantial difference in cell performance. 3.7 x 4 is 14.8 volts . . . right in the ball park for plug-n-play replacement of SLVA with Lithium. Yes, STORED energy is 1/2 but service life gets a real boost . . . and risk for electrically induced damage to the battery goes way down. The AeroVoltz 3x4 array I tested clocked in at just over 7AH capacity when charged on a 14.5V bus. Cells promoted in the wild are burdened with some outrageous claims for capacity . . . John Q. Public has few tools or skills to determine if his purchase was righteous or not . . . so the flim-flammers get away with it. MOST of the cells I've sampled off eBay were not worth the postage to get them onto my workbench . . . however, some are quite good. Balancing chargers are another story . . . but the bottom line is that the COTS offerings of lithium drop-ins for SVLA battery boxes don't come with a lot of hazard to anything but your pocketbook. As the lithium market matures, we may well be speaking of 16 volt systems for future airplanes. Bob . . . ________________________________ Message 4 _____________________________________ Time: 10:40:58 PM PST US Subject: Re: AeroElectric-List: Overvoltage crowbar availability? From: Justin Jones Bob, Do you have any of these new ovp modules available? Justin > On Dec 13, 2014, at 19:12, Robert L. Nuckolls, III wrote: > > At 20:43 2014-12-11, you wrote: m> >> >> Greetings, >> >> It looks like B and C no longer carries the stand-alone overvoltage crowb ar (at least I think that's where I bought the one in my LongEz). >> I know Bob is trying to get out of the parts distribution business. >> Does anyone else know of a source or should I just plan on building my ow n. (and if you have the link handy to Bob's schematic that would be great b ut don't search if you don't as I'm sure I can find it...). > > There is a replacement for the legacy crowbar modules > in the works. Boards are laid out and software is > nearly complete. Probably have some working hardware > in the next two weeks. B&C can probably still sell you > the older version as well. > > The new one is software based and much more immune > to nuisance trips. It's also packaged to look more > like an 'airplane part' than the legacy CBOVM > modules. > > > > > Bob . . . ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.