On 12 Jun 2013 at 17:06, Lawrence Rhodes wrote: > How about one of these [chargers] per cell ... less complicated.
Our old friend modular charging makes yet another appearance. ;-) He's been stopping by the EVDL periodically for about 20 years now. Here he has the potential to cause the same problem he did with a dozen chargers servicing a dozen 12v lead modules back in 1994: if one charger fails, you may not notice until you've driven the EV and destroyed its module (or, in this case, its cell) by reversing or overdischarging it. In fact the situation's even worse here, since there are about 4 times as many chargers required. Such a failure is thus 4 times as likely. And although I know nothing of "GWL Power," if the chargers happen to be of cheap generic sweatshop manufacture, assembled with lowest-bidder components and underpaid, overworked labor, that further multiplies the risk. For modular charging, you still need reliable cell-level monitoring to warn you and prevent such trouble. At that point, IMO, you might as well add a little more cash and get a real BMS. I'm barely getting my toes wet in lithium, so I'm not in a position to recommend anything, but there are plenty of others here who are. And even though LiFePO4 for EV conversions is still relatively new, it seems to me that we're starting to see some product combinations emerge as more or less popular choices. That doesn't guarantee that those combinations are reliable or long-lived, or even effective; but going for the popular choice might earn you a better shot at support from other users. For example, IIRC some folks here have pointed out significant limitations in the Mini-BMS. However, it's a widely used system, so there are lots of other users you can go to for help. Same with CALB and maybe Winston cells. Or you could decide that having dealer support is important to you with something as sensitive and expensive as a lithium battery, and spend extra bucks to buy a pre-configured, tested, warranteed battery system, with BMS and charger, from one of the EV component dealers. David Roden EVDL Administrator http://www.evdl.org/
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