Hello everyone. I'm an inactive PP SEL, dreaming of building a -10 and so I've been lurking here for quite a while. With no building experience I haven't felt that I've had anything to contribute, but this thread is beginning to parallel a
discussion over at the Cruiser's Forum, so I thought I'd offer a summary and a pointer. Think carefully before popping over there because that thread is over 3800 posts!
I have the following takeaways from that thread:
1)
Any battery chemistry can be dangerous if misused. I had a sealed lead acid battery that bulged and got hot because I stuck it on an old-fashioned Sears charger overnight.
2) Lithium iron (in its various formulations) is arguably the safest of the rechargeable lithium chemistries to date but
will be damaged by either overcharging or over discharging.
3) To mitigate (2), you
must have a high voltage disconnect and should have a low voltage disconnect, but if you'd rather destroy or damage the battery because you need to keep drawing on it (alternator failure in IMC comes to mind) then leave off the low voltage disconnect. The high voltage disconnect is critical to avoid bulging, rupture, or a possible fire.
4) A battery monitoring system at the cell level rather than total pack voltage must drive the disconnects. You can charge at normal pack voltages and still overcharge (and damage) a single cell if the cells are way out of balance.
5) In deep-cycle service cells vary little in their voltages once an initial balance is done, and the consensus is that routine balancing is unnecessary. In the electric vehicle world things are different, and I suspect airplane use is somewhere in between. It all depends on charge/discharge rates, and how deeply you're willing to discharge.
6) Lithium iron looks to be a great up-and-coming technology, but it's not a lead-acid drop-in replacement--the entire charge/discharge system needs to be tailored to its different requirements. Those folks over at the Cruiser's Forum who've implemented LiFePO4 with thought and care are quite happy with the results.
Doug