DC to DC charger

HMS Beagle wrote:
How large is the LFP bank again? It sounds like the DC-DC is severely limiting the charge that could be put into even a reasonably large bank.

On a boat, where this stuff is much more advanced, you'd have an external regulator on the alternator, large cables to the house battery, and be charging them at 100A. The charge profile can be set for LFPs and is close enough that an AGM start battery will tolerate it. Even with a 160A alternator, you'd still only charge at around 100A because the external regulator has a temp sensor on the alternator, and will derate it at about 100 deg C frame temp to keep it from frying itself.

A big advantage of LFP over AGM is that its charge acceptance does not fall off rapidly as it gets close to full. It is actually that, not any ability to accept more maximum charge (often less than good AGM in similar sizes) that allows faster recharge. If you are sitting in a campsite running low and want to start the engine to charge, you want to put in 100A for half and hour, not 25A for 2 hours.

not to worried about the charge aceptance although it is definatly an advantage. I worked on boat/sub stuff for 20 years totaly different game and there was no LiFePO4. thoes altanatores were special units desinged to put out far more amps and such than any pick up truck altanator.

also depending on the size of battery some one has you might be better off putting in the 25amps for 2 hours. generaly a 1C charge (100amps on a 100ah battery) will get you the rated minimum cycles, a 0.2C charge will get you the max life which is a pretty singnificant amount of extra cycles.

think of this as just a way to suplement charging of your house batteries using a proper profile, weather you have gel, agm, flooded or Li. Myself in my camper and my 5th wheel I have no charging from the vehicle at all, but that is changing with the camper as I am putting in a 20 to 30 amp dc charger. normaly my solar panels have me charged back up before noon, but if I am camping and we get dark for quite a few days I have the dc to dc as a back up charger, or to take the 22 amps my solar puts out and add another 20 to 30 amps of output to charge even faster if I need it. if you don't have a permantly mounted solar, or you just want to run the fridge on 12V while your driving it is good there making sure to charge by the proper profile for your house batteries. it also acts as a battery seperator so you cant pull down your starting battery.