On 16 Jun 2015 at 5:52, Paul Dove via EV wrote: > A battery monitor is fine battery management should be avoided.
In the early days of the EVDL, we debated (sometimes pretty strongly) AC vs DC motors and flooded vs AGM batteries. IIRC, though, there weren't many of the AGM crew who said "forget the BMS." It was pretty well accepted that AGMs would have a short life without some way to balance the modules' charges. Today many more people are using lithium batteries. They're are even more sensitive to overcharging and undercharging than AGM, and here we are debating BMS vs no BMS. Who'd'a thought it. Still, I have to say that thse discussions are worth having. But flat statements like the one above -- and (I admit it) my own "Don't," and your original "Skip the BMS" -- don't really advance the discussion. So, I'll qualify my statement, and I hope you'll qualify yours. Thousands of consumer products from electric toothbrushes to robotic vacuum cleaners and rechargeable electric lawn mowers have been built without BMSes, and with some of the dumbest imaginable chargers. Their manufacturers knew that most customers are way more interested in a low purchase price than in long battery life. But except for the very cheapest and crummiest dollar-store junk, anywhere you find a lithium battery in consumer goods, you find a BMS. And EVERY factory EV has a BMS, in fact a rather complex one. That should tell you something. The makers realize that most people don't babysit their gadgets' batteries. They also know that the consequences aren't just batteries that die in a year or two, some lithium batteries can catch fire, and some have. Lithium batteris just aren't as forgiving as good old lead, NiCd, and NiMH. The manufacturers don't want lawsuits, so they use BMSes with lithium. You do too. Yours is just manual. And that can work as long, as you're thoroughly knowledgable and attentive. But lots of people aren't, and I think you have to take note of that before you advocate dumping the lithium BMS. EV hobbyists should realize that just because you've run your EV for X years and its cells are still in balance without a BMS, and Y number of others have, that doesn't mean it'll work the same way for everyone else, with every cell, every vehicle, every driving style, every charger, every climate. I don't know enough to dispute the possibility that a bad BMS is worse than no BMS. Maybe that's true. But even my limited experience tells me that a good BMS works pretty darn well. I would not use a lithium battery without a BMS, period. Some other highly knowledgable and experienced people here and elsewhere come down on that side too. Paul would, and does, along with some other (often very vocal) BMS opponents. To the EV hobbyist, I say : consider both sides of this discussion and the possible consequences, then decide what suits your situation. David Roden - Akron, Ohio, USA EVDL Administrator = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Note: mail sent to "evpost" and "etpost" addresses will not reach me. To send a private message, please obtain my email address from the webpage http://www.evdl.org/help/ . = = = = = = = = = = = = = = = = = = = = = = = = = = = = = _______________________________________________ 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)
