This is kind of long (I tend to run on, sorry). Please bear with me and I'll eventually come to the point.
I'm sort of the electronics equivalent of a shadetree mechanic. I've hacked (in the good sense) electronics since I was a teenager. ICs weren't really available to hobbyists then. My early tinkering was with tubes, germanium semiconductors, and eventually silicon semiconductors. You young whippersnappers don't know what you've missed, not getting to play with 6SL7 and 6V6 tubes, inefficient selenium rectifiers, and 800 volt B+ supplies (yeah, I got zapped a few times). So even though I'm a EE dropout, I have a lot of years of messing around with electronics and, with a little research and luck, making things work. I'm glad to say that despite doing some moderately stupid things, I've never started any fires. I want to keep it that way, which is the reason that when I started using lithium batteries for a few tasks, I did NOT try to hack up my own lithium batteries. Instead, I did my homework, researching who made reliable batteries with charging systems. Then I bought them. Yes, they cost me more than buying bare cells on Ebay and tacking them together -- quite a bit more. They cost me more than Aliexpress junk. But they worked right out of the shipping box, delivering their rated capacity and then some. And they STILL work. The batteries I bought from Li Ping in early 2012 are still producing over 90% of their rated capacity. You'll find lots of lithium hackers in Youtube channels, forums, and social media, who swear that they don't need no steenkin' BMSes. You'll even find some who claim that BMSes *cause* fires. You can identify these folks by their frequent use of the phrase "bottom balancing." With all due respect, and at the risk of offending someone, I suggest that you not listen to them. Your mobile phone has smart charging and discharging control. (The charger IS the BMS because phones need only one lithium cell.) Every laptop and tablet has a smart BMS and charging/discharging control. Every good lithium power tool and home appliance has them. Every production EV has them. With some notable exceptions (*cough* cheap Chinese hoverboards *cough*), these are lithium battery systems designed by experienced engineers. Some engineers are better than others, and some bean counters managing them are more ethical than others, but by and large you can reasonably expect that you can leave a lithium-powered commercial product charging on your kitchen counter and it won't burst into flames. That's because it has appropriate charging / discharging control. There are people on the EVDL who have the engineering chops to design a lithium battery system that maximizes the life of the cells and prevents such disasters as fires and explosions. However, I'm not one of them. With all due respect, from what you've posted here, I don't think you are either. In fact, one of the EV conversion pioneers that I greatly respect, Bob Batson of EV America, didn't try to design his own lithium battery system either. He referred his customers who wanted lithium to companies with more experience with it. More recently he's taken on an experienced supply partner for lithium. He wisely knew and knows his own limitations. http://evamerica.com/flux.html I'm not recommending Bob's batteries. I can't, since I haven't used them. I'm just pointing out that designing a safe and long-lived lithium battery for an EV is not a trivial project. It's not (IMO) a good one for EV hackers like me. I strongly suggest that instead of jumping in feet first and maybe having to jump out and run really fast on singed feet, you keep using lead for a while. Save up your pennies until you can afford to buy a well designed integrated lithium battery SYSTEM (cells, BMS, charger). It might be boring, but it will help avoid the kind of excitement that you probably don't want. 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 Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
