This article focuses on sailboat LiFePO4 battery installations and the equipment and wiring changes we need to make to the electrical system in order to install the technology. “Lithium Batteries for Small Boats” considered some of the less frequently explored differences between LiFePO4 and lead acid battery systems and why those differences are important for a small boats electrical system. This series does, however, focus on the needs of sailboats. Super yachts, power boats, fishing vessels, commercial vessels etc. (and maybe sailboats bigger than 50 ft.) likely have different constraints and may therefore need to reach wholly different conclusions.
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A few (more) comments:
1) Charging LiFePo4 directly from an alternator is not, in and of itself, a faulty solution provided that you have a modern regulator programmed correctly, you take reasonable precautions to ensure a BMS load dump doesn’t fry your alternator diodes (Balmar and Sterling both make alternator protection devices), and you have a means of keeping the start battery topped off (even a low output DC-DC charger works fine for most installations). I understand that you’re trying to educate the newbie here and that charging the lead acid battery directly is the safest way to go (especially for internally regulated alternators), but people shouldn’t write off the benefits of direct LFP charging. The thrifty among us might easily buy an older Balmar external regulator now that people are upgrading to the Wakespeed and Zeus, and thus have adequate control over alternator output. I would also mention here that if you are charging the start battery directly, alternator output will decrease precipitously at around 80% charge. That means not only is your start battery taking longer to charge, so is your lithium bank. I don’t know how this works in practice. Maybe the DC-DC converter will pump enough amps into the lithiums to keep the charge rate higher.
2) Many marine electrical experts have eschewed the use of a 1/2/B switch for LiFePo4 installs. I think I read somewhere that momentary combining of chemistries may be OK according to recent ABYC (someone check me on that) but to me that means combine to get your engine started. Now you need to ask yourself if your LiFePo4 battery bank can handle that amperage load. More dual purpose LiFePo4 batteries now available on the market.
3) I would provide LiFePo4 isolation with a 1/2/O switch after the Class T for safety. I think that this is an ABYC requirement too. Not sure a 1/2/B switch is really the proper LFP isolation.
4) As for alternator sizing and load management, this is another good reason to have an external regulator that you can program to account for belt sizing (essentially, derating the alternator’s output based on field voltage input), and for alternator temperature to avoid overheating.
I think that if someone wants LFP which is super simple and least expensive, your strategy is a good way to go but people should understand the limitations and the risks.
Totally confused!
Sorry to see PS has morphed into crappy YouTube videos and advice from persons who blah blah too much. Just another bought by publication. So sad!
Great article. The only bi-direction DC to DC charger I’ve heard of is by Sterling Power? Its availability in Canada is more limited than some of the other brands. I noticed you did not specify any brands in your article? The technology is changing fast though so perhaps we’ll see others. It would be nice to see a multi channel charger that will charge lead acid and LiFePo simultaneously.
Hopefully, PS will string your articles together somehow so that when I read them again I don’t have to search for part 2, 3, etc.
Stephen Rietzel’s remark about stringing the articles of this series together is one I want to see also, as I’m about to refit a new boat and will be going with LiFePo4. This series is quite timely for my purposes.
I would love to see brand name suggestions, while recognizing that new gear for a new-ish technology of this sort comes on to the market with some frequency. When I wrote for SAIL, l would often mention a brand name I used, knowing full well that my editors would add in the names of other manufacturers (often advertisers of course!), giving readers options they could research and choose from if my solution didn’t work for them.
I would also – and this just might be my lack of knowledge of circuitry – like to see the above battery configuration diagram presented as a proper circuit diagram so that I can comfortably use it as a template for my installation.