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Old 11-08-2019, 03:12   #1
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Alternator for FLA starter batteries and lifepo4 house?

We're installing Relion batteries for our house bank and of course the "drop in" marketing is not really accurate. We have solar and wind that will be the main charging source and a generator/shore backed Victron Multiplus as additional charging.

The 2 Yanmar 4jh57 engines have 125 amp alternators that currently charge both the starter and house batteries. I've received conflicting info about whether the current engine charging is okay or not. My independent research indicates it isn't.

The alternators will either overheat from too much draw of I will damage the lifepo4 from voltage that's too high.

At the moment I'm considering simply removing the charging from the alternator to the house bank and use them only for the starter. Not that big of a deal since we're a sailboat and have only run the engines for 300 hours in two years (5500 nm) anyway.

Any opinions on this?
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Old 11-08-2019, 04:19   #2
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Re: Alternator for FLA starter batteries and lifepo4 house?

I have Yanmar 4jh3e with 80A alt and lead starter and lifepo4 housebank. The same problem as you and my solution was a Sterling Pro Alt C that charges both the start and house batteries with different charge profiles (lead/lifepo4). It also have a temp sensor that sense the alternator temp and dial the current down when the alt get to hot.
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Old 11-08-2019, 10:06   #3
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Re: Alternator for FLA starter batteries and lifepo4 house?

First off, note that keeping a dedicated Starter topped up is a tiny tiny load, as in single digit Ah per startup.

and the fact that you can use cheap batteries, replacing every 3-4 years, care concerns on that side are almost trivial.

Compared to deep-cycling House, much more expensive per Ah, much bigger capacity, want to optimize longevity, potentially cycling through hundreds of Ah per day.

Therefore best practice is to wire all significant charge sources direct to House, optimizing the charge profile for its care needs as the batt mfg specs.

With an alternator going to LFP that requires current-limiting adjustable custom profile VR like Balmar MC-614, or Alt2B or B2B unit(s) like Sterling's between the alt and House bank.

From that House circuit to Starter, an inexpensive VSR or Echo Charger will do just fine to keep it topped up.

Of course if you do not see your alt as a significant charge source, solar and genset cover your daily usage just fine, then skipping all that and dedicating alt output to Starter batts is fine.

Most owners with big House banks want to take advantage of all available sources.
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