Chris, I have 40 TS-LFP100AHA cells in my Gizmo and now have nearly 17,000 miles on the pack since January 2010. I think that the problem with the bad reputation of ThunderSky batteries stems from some early days and also from many people overcharging them. I'm not having any issues with my pack. I haven't even had to balance the pack since July 2011. I did a top balance and then took the balance boards off and then did weekly then monthly and finally went to bi-monthly checks. I did install a version of Lee Hart's BattBridge. Other than that, I haven't done any thing else other than count Ah and make sure my charger stops at 3.455V/cell. I'm thinking of going to a bottom balanced pack so I don't have to worry about the bottom end in case of a deep discharge.
I don't know how someone can justify the claim that CALB is good for power but not range. Doesn't add up. My recommendation is to go with a set of CALB CA (gray) 100Ah cells. If your equipment can handle it I would go with 46 cells so you have an even number and just use a BattBridge type circuit if you are willing to do some hand measuring of the cells periodically. This also assumes you have an Ah counter of some sort. I have a CycleAnalyst for that. Have your charger set to charge to 3.5V/cell and turn off when the current drops to 5A. Bottom balance your cells at something like 2.8V and make sure you have absolutely NO unbalanced loads on your pack and you will do just fine. If you aren't comfortable with such a minimal BMS setup as that then get a BMS with a good track record and install it exactly as recommended. I know that many say you have to balance on every charge. My experience shows that with a pack of good cells this simply isn't the case. Several people told me that if I didn't have a BMS on my pack that it would go way out of balance and do so rather quickly. Over two years and I don't see it. If you install a BMS I recommend you follow its instructions to do the initial balance of your pack and then lower your ending charge voltage to 3.5V/cell and 0.05C and only do a balance again when the BMS indicates one is needed. Note that with a BMS installed it is very likely that you will in fact have to balance your pack more often than without one since it is very difficult to get the load on each cell exactly the same. What ever you do, read up on the pros and cons of each situation you are considering so you know what to expect. Also, if at all possible, be sure to play around with a cell or two to get a feel for how they behave. You can do this with a bench top power supply, a way to measure current (which the PS might do), a separate volt meter to measure terminal voltage, a way to discharge the cell like some nichrome wire, and some time. These are not your lead acid, NiCd, or NiMh cells. BTW, with my 12.8kWh pack I can easily get 70mile range out of my Gizmo. My average consumption is 169Wh/mi measured from the wall. Charging efficiency is 80-85% so your estimate of 200Wh/mi is likely reasonable. On Mon, Sep 2, 2013 at 1:04 PM, L. Chris Hager <[email protected]> wrote: > > > Qs about batteries for a VERY light car-- 580 lb w/o batteries > > > I have a British sports car from the 'microcar' era-- a 1959 Berkeley SE 328 > (yes, the size of the orig. motor-- 328 cc; Google 'Berkeley 328' or 392 in > google pics-- you'll note that it's very aerodynamic, an ideal small project. > They came with an 18 hp 2-stroke motorcycle motor, and were only capable of > about 65mph. This model weighed under 700 pounds from the factory, so, > stripped of the ic motorcycle engine, the transmission and gas tank, my > project will start at about 550 lb-- plus batteries, bms, and > motor/controller. I obtained a Berk previously converted to electric in the > late 90s for competition; it beat all comers in autocross, and won a 7-day > EV road event one year. So I'm aiming to get it back on the road, but the old > batteries and bms are long gone. I got the car with a new 144v Solectria AC > motor (yeah, note: AC, not DC) and Solectria controller-- part of the > purchase deal. > My goals are moderate speed (v short burst to 65, a short cruise at 55-60, > maybe 20 mi, or longer cruise at 45-50), moderate acceleration (no showing > off), and a range of 60 or so, assuming its not running wide open -- more > like 40 mph average for the trip. I feel there's no way could I load up this > little car withlead-acids. In a note from L H in MN, L says he thinks that 60 > mph in a Berkeley probably only takes 5 HP. 1 HP is roughly 1 KW. So the 144v > pack needs to supply 5000w/144v = 35 amps. Peak power needed to accelerate > and climb hills at moderate speeds will be about 3 times this or 100a at > 144v. Roughly, he says, I'll probably use about 0.2 KWH per mile. A 20-mile > range thus takes 0.2 x 20 = 4 KWH, and a 60-mile range takes 12 KWH at > constant speed on level ground; double for hilly driving or frequent > stop-n-go. As the KWH and pack voltage tell the needed amp-hour capacity of > the pack, his estimate then calls for 12 KWH > /144v = 83 amp-hours. So I feel OK about using 100 a-h cells-- and more > might be hard to fit into so small a car. He notes that for a 144v pack, I'll > need 45 cells. Each cell weighs 7.5 lbs, or 8 lbs with hardware, so I'll have > a 45 x 8 = 360 lbs pack, plus BMS. Final weight with me driving: not much > over 1000 lb! > SO, my Qs: If this were your project and you were opting for lightweight > batteries, what chemistry would you chose-- I gather there are two different > Lithium chemistries (Li and Li-Fe, I guess- or suggest any other chemistry > readers can steer me to-- which sounds unlikely). I'm prepared to put upwards > of 5 grand into the batteries and batt. management. If lithium it is (which > type?), then further: What Brand? I've heard a lot of bad things about > Thundersky, and although I'm told CALB is better, one veteran of EVs has told > me CALB is good for power, but not for range (not sure of the physics of > that). So the big questions are: what chemistry, and what brand of battery > seems to have a superior record? And THEN: does that brand also offer a > batt. management system that is reliable? If not what BMS yould you buy? Any > and all information and opinions welcome! Thanks, Chris in Northern VA > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: > <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20130902/f8d28f6b/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) > -- David D. Nelson http://evalbum.com/1328 http://www.levforum.com Nokia Lumia 920 Windows Phone 8 _______________________________________________ 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)
