For the no-BMS crowd, a simple approach are the Cellog 8m or 8s (8s does data logging) for about $14 or $24 respectively. Each device is connected to up to eight cells. So for 50 cells you would need seven Cellogs or just move one between 7 mating connectors. Very accurate devices that also provide programmable LVC & HVC alarm signals.
Definitely the "poor man's" BMS but very popular. The device takes its power mainly from the first two cells, so could lead to imbalanced cells if always left connected to the mating 9-pin connector. But if just monitoring during use, it is not a big deal. The folks out on endless-sphere have come up with a solution that balances the devices power across all cells evenly but it seems like a lot if work. Good luck On Feb 15, 2013, at 11:14 AM, "Pestka, Dennis J" <[email protected]> wrote: > If you don't go the BMS route, does anyone make a good reliable instrument to > monitor ~ 50 cells. > You wouldn't think it would be that hard to make some visual > display/meter/instrument/? that would let you keep an eye on 50 cells. > That way, if you're concerned about a BMS and all the issues we've heard > about, you could take it on yourself to monitor the cells. > > Anything available out there that I'm missing ? > > Thanks; > Dennis > Elsberry, MO > http://www.evalbum.com/1366 > http://www.evalbum.com/3715 > > > > But suppose there is no BMS. Lithiums do not have the large resistance > increase as they approach dead. The weakest cell keeps right on trying, > right up to a few moments before it drops dead. At the 10.5v cutoff, you > may have 3 cells at 3.1v, and one at 1.2v. The 1.2v cell's voltage won't > bounce up to a "safe" voltage range. It has been seriously damaged, and > won't recover. And without a BMS, you won't *know* you've damaged it, > and may blithely keep using it, potentially leading to a fire! > > So that's the situation as I see it. When everything is fine, it works. > When something goes wrong (like the cells wandering out of balance, or > leaving the lights on, etc.), there is a risk of failure. If things go > very wrong, the failure can be dramatic! > -- > For every complex problem, there is a solution that is simple, obvious, > and wrong. -- H.L. Mencken > -- > Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.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) > _______________________________________________ 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)
