I've read this thread with interest and, with one season's experience with my 540Ah of
LiFePO4, I thought I'd share my experience.
My
installation is a practical one. Alternators are expensive and an 'investment' - at least for me. I have
Volvo D2-40s in my
catamaran with the 115A 'dumb' alternators that have been the subject of much discussion on other threads. (For dumb - read fixed, internal regulation).
I was concerned by the theory put forward in other threads that these alternators would self-destruct after a while due to prolonged running at high output
current so I instrumented them with temperature sensors and monitored their performance. In short, the stator
cooling fins never reached more than 100C (212F) when I pushed them as hard as possible (empty
batteries, high RPM). More normally, at cruising RPM, they were 80-90C. I considered this to be OK, compared with the design spec for automotive alternator performance. (A document that has been referenced in other threads.) The output was typically 90-100A, falling to 80-85A after a while. (One engine). With 2 engines, I can see up to 150A but I generally have no reason to run both engines at once (at cruising rpm anyway)..
My alternators are linked to my batteries (LiFePO4 - house and LA for start) through a no-drop charge splitter (Mastervolt - rated to 130A). This may be the reason for the lower than expected output currents. However, I consider these charge currents sufficiently low that the alternators are running 'derated'. So, for steady-state
charging, the output currents and temperatures are (in my view) perfectly acceptable.
When the bank is 'fully charged' (13.8V is the limit I
work to) the alternators are disconnected. I throttle back for a few seconds as a courtesy to the diodes (still connected to the LA batteries anyway) and disconnect the charge bus from the LiFePO4 bank. If I forget, my BMS will complain at me till I do disconnect them or if I'm really persistent, it will do it for me. (DIY BMS).
I understand that others will want to take advantage of the high charge acceptance rate of the LiFePO4 banks and I will, in the future do so as well. However, I'm not prepared to replace 2 perfectly good alternators that have life in them just to save a few minutes charging time.
My view on using the engines is that I only use them when I have to. My main charging is from
solar. I'm happy to take the 'reduced' charge rate from the alternators (still much improved over LA) since its not my primary charging source. Moreover, I still have to remind myself that these batteries are happy NOT to be fully charged all the time and so we are content to float around in the middle somewhere just accepting what charge comes our way from
solar or
wind. If we need to
motor, I decide whether to take some charge (or not). On a sunny day, I'm happy to
motor without taking charge from the alternators (to the house bank) - it saves
fuel.
(I note the interest in MOSFET switched rectification. I have a board for my
wind generator sitting on my desk. Its one of my
winter projects. I also have a board for an ideal diode to allow the charge bus to provide currents to the house loads while the House bank is disconnected from the charge bus but I'm not going to hijack this thread.)
Its an interesting topic - I'll be interested to see the final choices and reasons for them.