backchannel: case study - direct charging LFP in a Rav4

from this thread on /r/overlanding

TL;DR

a small DC-DC (like 20-30A) would be simplest, in the sense that there would be less homework.

more info and caveats about the DC_DC approach

more info and caveats about the “isolator” (combiner) approach

LiFePO4 can charge quite nicely from a combiner:

HOWEVER, the setpoints on voltage sensing relay mentioned in the other thread will not allow the batteries to disconnect normally after charging stops:

CUT-IN VOLTAGE: 13.3V
CUT-OUT VOLTAGE:12.8V DC

Compare the cut-out voltage to LFP’s resting voltage to see why this happens. Workarounds in the link above.

I do not necessarily suggest direct-charging LFP for the general public installing their first alternator charging setup. I do suggest testing it for people who already have a combiner installed, or for people who have working knowledge on how relays, LFP, and alternators work.

Updated: