Transition to LFP house bank

Boat Systems
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I did a 40 nm engine mount checkout voyage which went really well in terms of mounts and exhaust plumbing. However, I did experience a broken alternator bracket which was completely unrelated to the mounts and easily fixed. I also spent a night at anchor during which I realized my two 110AH house AGMs were compromised to the extent the bank would only deliver about 50 AH.

I did not spend a lot of time troubleshooting. I bought cheap AGMs a couple of years ago with the thought I would be upgrading to Lithium at some point in the future when I got up enough courage to face this new technology. Yea, I know, it’s not new, but it is to me. So that point has now arrived.

Anyway, to celebrate the end of the engine mount saga I decided I would launch into a house bank LFP upgrade, how hard could it possibly be? More famous last words have never been spoken :rofl:

So I bought an Ecoworthy 280 AH LFP battery. It is a cheap LFP but a fellow on YouTube I respect (Will Prowse) tested and tore one down to look at build quality. He gave the battery a thumbs up in the “cheap LFP” category.

Standard LFP batteries are not good start batteries (although they have been used to start) so I kept my old AGM start which was still in pretty good shape.

Since only my solar controller charge source had a Lithium profile I connected this directly to the LFP battery. I connected shore power and regulated alternator to the “charge bus” which charges the AGM start and also provides power to a Victron DC to DV charger which converts the AGM charge profile input to a LFP appropriate charge profile. BTW, the Victron can be configured for a variety of chemistries. It also has Bluetooth which allows this configuration to be done from the phone. The Ecoworthy battery also has Bluetooth. I downloaded the “overkill solar” app to access the battery and the integrated Battery Management System (BMS) so I can see all the BMS settings, cell voltages and so on. It is a real game changer in terms of visibility into what is happening with your batteries.

Anyway, I got it all put together and, after a week, I think I am sneaking up on an understanding of how it all works, Especially the charging and cell balancing element which took some serious time staring at what was happening with cell voltages as I applied charge current , did a discharge session, rinse and repeat about twenty times.

One thing I found is that there is an incredible amount of BS flying around regarding LFPs. There are a lot of amateurs (like me) pontificating without having a clue what they are talking about. Warning issued.

So I have completed testing on shore power and solar charging, They work, I have not tested alternator charging yet. That will be a biggie. One sweet thing about the Victron is that its max current transfer is 50 amps but it can be throttled all the way to zero in 1/10 amp increments. This is important because one feature of the LFP battery is its ability to accept a LOT of current for a long time. I have a 125 amp alternator on a serpentine belt but my alt probably will not like running at a constant 50 Amps for 5.5 hours while the LFP charges. I do have a belt manager on the Balmar ARS regulator so I have a second way to reduce alternator output but that requires some hands on work with the regulator while the Victron config is just an app away.

One new concern with LFP is the presence of the BMS. This electronic device (in my case embedded in the battery case) monitors temp, input and output voltage and current and cell balance (and probably other stuff) constantly. If it detects a fault in any of these parameters, it will shut the battery down until the fault is cleared. Now this is an interesting feature. I can remember a time approaching Pillar Point Harbor in the fog at midnight. If I had had LFP and the BMS had decided this would be a good time to dump the battery that would have been interesting. I do have a backup plotter on internal battery but everything else goes dark. I have to figure out a way to switch the +Bus to the AGM battery in an emergency.

I realize I am babbling but I thought I would keep you all updated on how this goes.

Some interesting LFP related links:

Will Prowse videos/battery reviews ++

https://www.youtube.com/results?search_query=will+prowse

DIY Solar forum (has a Marine category + much good info/resources)

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OK, have done a little cruising with my new LFP battery online and I am very happy.

I literally spent 5 days at anchor, freezer on full time. Depth and wind on 24/7, laptop charging, tablet/phone charging, anchor light etc. and only my 200 watt panels for charging the battery. Best I can get out of the panels is around 160 watts. I left the Anchorage with more power than when I arrived.

Extremely pleased so far

For emergencies ( for example. LFP drop due to internal BMS detecting problem) I have a strategy to quickly reconfigure to run all loads on my 100 ah AGM.

Took a while to sort out the new charging requirements and unique characteristics of LFP batteries but I made some progress on this and so far this system has been fantastic.

LFP batteries charge more efficiently than AGMs do and this may account for my experience at anchor. Alternatively my AGMs were just ready to give up the ghost…don’t know. Either way the LFP has been a big improvement. Overall project cost was about $800.00 + sweat equity. Weight reduction of about 100lbs and a lot more room in my battery box.

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This is great to hear Mike, as I am in the process of updating my AGM’s to a new engine AGM with a parallel pair of new 100AH Li batteries. I’ve been using 200W of solar with a pair of aging 6v 200AH AGM’s for the past 2 years and while it worked pretty well, the effective 100AH would be marginal during a cloudy spell with the fridge running full time.

This year I’m adding a DC-DC with an input for both the alternator and a dedicated 100W solar panel for the AGM. Once fully charged, that will then be delivered to the house bank.

I’m also adding a small 1000W inverter for occasional AC needs.

Your results are encouraging!

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I think you will be surprised at how well these things work. The only downside, and it is not that far down, is you do have to rethink the configuration and have little different mindset re charging, But no big deal, esp. since this tech is quite interesting and well worth the effort if my initial experience is any indication.

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Nice job Mike. I did a conversion three years ago with three Victron 200Ah LFP house batteries and have been thrilled with the results. I have an AGM starter battery. I do not have Solar, but I anchor out for several days at a time. I have a 250 amp alternator which charges the system very well. I can anchor out 3 to 4 nights with my 14’ fridge/freezer cooled by a Fridge O Boat refrigerator, running all the lights, computers, and everything else we use. I rarely let the system go down below 50% charge… I commonly do run the engine every other day or so to heat up hot water. It does not need to be charged over the winter because LFP batteries tolerate cold very well. I had mine installed professionally, which was quite expensive, but it works great.