Hi Chris, I actually have a very similar setup as you are describing; except my car weighs at least twice as much. See: www.evalbum.com/2778.
I have a 1993 Honda del Sol with 45 ThunderSky LiFePO4 cells. It has MiniBMS boards on each cell as the monitoring solution. It weighs (after conversion) at 2550 pounds. The cells have been working fine for my use. I have about 3 years and 20K miles on the conversion. Given your usage, the only concern I would have would be fitting the cells into the car. If you can get them into the car, I think they would work very well in this application. My conversion really tries to draw about 200-300A for aggressive acceleration, but it also weighs more than twice as much. I draw about 70A at 140V to cruise at 60 mph on the highway (about 9.8kW). I have about 50 miles range. It may be a little more, but I've driven 50 miles. The del Sol is NOT very aerodynamic. Much of my driving is at 55-60 mph. The ThunderSky cells really don't want to provide more than 200-300A (300A tops). I think they would be happier delivering 100+ amps, so I think your expectations would fit very well with their capabilities. I think the CALB cells might provide a little more current. Today, if I was building a vehicle, I would probably go with the CALB. I have the MiniBMS to alert for undervoltage, top-balance the cells and disable charging if the charger tries to over-charge. They are actually a backup system in both cases. If I'm keeping range where it should be, I shouldn't drain a cell too far. My charger (Elcon 2000+) normally tapers and terminates charge before any cell gets high enough to alert the MiniBMS. The MiniBMS boards do have a power resistor to shunt extra charge off and help top balance the cells. It is important to balance the cells. I had unbalanced cells when I first bought the conversion and possibly caused some damage on two cells. My undervoltage alert was too quiet to hear and I kept driving. I found that two cells were 20% below the others in total charge. I used an RC charger to top them up. I found the MiniBMS shunts aren't enough to balance a set of cells that is too far off. The charger hasn't started its taper yet and that causes the shunting time to be very small. The same two cells are still in the pack, but I'm watching to see if they fail early. If you look at the photos of my conversion, you will see that 45 cells do take quite a bit of space. My recent installation has insulation and protective covers around the cells. I also have clear plastic over the cells to keep curious fingers away from the high voltage. If you are in a cold area, I would recommend the insulation and/or heaters under the cells. Their performance does get quite a bit worse as temperatures get near or below freezing. You get voltage droop much quicker under even moderate load when the cells are cold. (The pictures with insulation aren't on the evalbum page yet). I have both insulation and heaters. Last winter, I only used the insulation as the heaters weren't hooked up yet. That worked OK, but performance would be better with the heaters keeping the batteries to 70F. I hope this helps. Let me know if you have any questions. Mike > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of L. Chris Hager > Sent: Monday, September 02, 2013 2:04 PM > To: [email protected] > Subject: [EVDL] Questions about Lithium batts for a VERY light car-- under 600 > lb w/o batteries > > > > 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) _______________________________________________ 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)
