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« on: February 08, 2023, 06:14:20 PM »
I’m going to venture forth with my opinions on this subject even though some may not agree. I’m right in the middle of reconfiguring my boat’s battery and charging systems to incorporate LiFePO4 for the house bank. My recommendations to MQ are as follows:
1.First, spend some more time educating yourself about incorporating Lithium. As Maine Sail says, Lithium is not a drop-in replacement for lead acid. There’s more to consider than you see at first glance. I’d recommend watching the video seminars on YouTube from Pacific Yacht Systems (Jeff Cote) on the subject (yes, I know, he’s long winded, but there’s good information in there.) Also Maine Sail has several good write-ups, as well as Nigel Calder’s extensive writings and his videos on YouTube.
2.One of the above authors made a good analogy, which was that LiFePO4 batteries are like marathon runners, and lead-acid starter batteries are like sprinters. Starting an engine requires a sprinter – big push for a short duration. This is not what LiFePO4 batteries are designed for. They are good at providing a strong, steady output for long periods of time. The three authors above all seem to agree that using a LiFePO4 battery as a starter battery on a regular basis is not recommended.
3.You mentioned that you were going to have the DC to DC charger charging the starter battery from the house bank. In my opinion, that’s backwards. Unless you are also using solar, the DC charger only comes into play when you are charging via the alternator. When you crank the engine, you are only draining the starter battery by a couple of percent in most cases, unless your engine requires some serious maintenance. (This is why most internally regulated alternators have a VERY conservative charging profile – it only takes a few minutes to fully recharge the starter battery.) So to me, it makes more sense to have the DC charger look to see when the starter battery has 13.6 V on it (i.e. it is being charged by the alternator), and draw from that side to also charge the house bank, which will likely be in more need of charging. The starter battery will be recharged in short order, and then the DC charger and alternator can focus on the house bank.
4.There are many misconceptions about Lithium batteries – especially the issue with flammability. Maine Sail does a good job of putting this to rest (as does Nigel Calder), clarifying that the LiFePO4 battery is very different that the earlier Lithium Ion batteries that made the news so often. The primary concern for fire with LiFePO4 would actually come from situations where a dead short in wiring occurred that would allow the battery to pump out vast amounts of current, melting the wiring. However most of the batteries being sold today have battery management systems that would shut down the battery in these situations. That BMS, combined with an appropriate Class T fuse in the main wiring configuration should greatly reduce this risk. The other situation to guard against is using a 1/2/both switch and combining a heavily discharged starter battery with a fully charged LiFePO4 bank. The large voltage difference would cause a big current spike, and again could lead to a wiring meltdown. In my configuration, I’m using a keyed switch hidden away from passengers that will allow me in an emergency use my house bank for starting the engine, but only after I first pull the fuse on the starter battery so that the two banks are never linked.
That’s my nickel’s worth. Is it worth installing LiFePO4? I think so – for nearly the same cost as replacing my 4 dying Trojan T-105’s I’m getting about 220 amp hours, of which I can actually use about 175 AH on a regular basis (and more if I really need), whereas the Trojans gave me 420 AH, but I could only use about 35% of that on a regular basis or 147 AH (sometimes 200 AH if I pushed it hard, but you pay a price in longevity for that). Not to mention the far longer lifespan for the LiFePO4. And I can fit the two lithium batteries easily into the battery box, with enough room to also mount the DC to DC charger in there and do a nice, neat wiring job for my main unswitched bus, fuses, etc.
OK – I’ve stepped down off my soapbox…