Re: LiFePo4 batteries: Twin 24V Alternators on the main engine

Scott SV Tengah


My first priority would be to increase your solar output. We are at 960 and have figured out a way to add 380*2=760w of hard panels over the Bimini. Assuming they're installed correctly, they just work. Take a look at half cut cells as they tolerate shading far better. 

Regarding alternators, I will preface by saying that I stuck with the standard Mastervolt 110amp 24v alternator that is spec'd on most 54s. I changed the external regulator to the Alpha pro II, which has a lithium profile. It outputs anywhere from 80-90 amps at my miserly 1300rpm (per Amel, the most efficient speed, maximizing range). I disagree with Bill that it has no meaningful impact on generator usage, at least in my case.

We have 450AH of Victron lithium batteries. My 11kw Onan has 200amps of 24v charging capacity. As you know, the lithium batteries will take full current until almost full, so my generator usage is very optimized.

I don't know how much you motor, but let's assume 400-500 hours. 400 hours X 80 amps from alternator = 3200 amp hours into my batteries. Even at my 200 amps of charging via Onan/230v chargers, that's 3200/200 = 160 hours of generator usage saved per year. Don't know about you, but as a result of that, we rarely run our generator and we're cooking with electric and running the dishwasher daily and water maker every third day or so.

For me, nearly eliminating my generator usage (we do run it now and then to make sure it doesn't become a rust ball) is not about saving diesel costs. It's about maintenance and the associated time to source diesel, replace parts, change oil, etc. And listening to that damn Onan. And of course, environmental considerations.

Another side effect is that while my batteries will happily accept 200amps until nearly full, they actually are happier taking 80amps. This gives them more time to top balance as they get full.

I know this doesn't help you decide between keeping your current setup or adding more alternators, but just want to state that our 24v engine alternator contributes a meaningful amount without adding additional operating hours.

How long will you be in Whangarei? We are in Fiji now, but intend to head there for cyclone season.

2007 A54 #69
SV Tengah

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