According to whom? Sent from my iPad
> On Oct 13, 2014, at 1:55 PM, Lee Hart via EV <[email protected]> wrote: > > Cruisin via EV<[email protected]> wrote: >>>> Using a meter to turn off a charger at a pre-programmed voltage >>>> can be very risky. > > Paul Dove wrote: > >> Problem is no one has actually proved that with experimentation. > >> Not in any of my reading. You can believe what ever you like. > >> > >> I have used ammeter for 2 years now. The voltage always end > >> exactly the same. The next day the pack is the pack is exactly 147 > >> volts. > > Martin WINLOW via EV wrote: >> The problem I have with relying on simple pack voltage measurement >> to control the charger is that eventually, as the pack ages, one or >> more cells are going to go out of balance, become the 'weakest link' >> and cause the capacity of the pack as a whole to unnecessarily >> reduce. From a safety perspective (safety of the pack) I suppose the >> Light-meter method is as good as any but it is the vagueness of its >> operation that is the issue for me. > > When the pack is new, and if the cells are already well balanced, then > measuring the overall voltage works. > > But, the cells might NOT be initially well balanced. If you bought them from > the cheapest source, they almost certainly didn't take the time to balance > them for you. > > Just because the cells are at the same voltage doesn't mean they are > balanced. Voltage is not a good indicator of state of charge for lithium > cells. > > Then, the cells are going to age. Time is not likely to improve them; instead > it's almost certain to make them worse. > > Finally, consider this. You *will* use the pack until it fails! And the > failure modes of lithium cells can be catastrophic (early destruction of an > expensive pack, serious fires, etc.) With no BMS, nothing will detect, warn, > or prevent disastrous failures. > > -- > Failure is only the opportunity to begin again more intelligently. > -- Henry Ford > -- > Lee Hart's EV projects are at 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)
