Upgrading boat to AGM Starter and LiFePO4 House batteries

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rob-crawford asked Jun 10, '21

Upgrading boat to AGM Starter and LiFePO4 House batteries

I am planning to upgrade the old Lead Acid batteries on my power boat this year. The current configuration looks like this;

My plan is to replace the starter battery with a dual-purpose AGM battery and replace the house batteries with a pair of LiFePO4 batteries. My understanding is that I will need to install a DC-DC charger between the starter & house batteries to adjust for the higher charging voltage for the Lithium batteries, but I wanted to confirm this. It seems like the DC-DC charger should be installed next to, or in place of the battery combiner (between the starter and house batteries), is this correct? Thanks for any guidance.

MPPT SmartSolar Orion DC-DC Converters not smart

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randy-putnam answered · Jun 10, 2021 at 01:24 PM

This year and last I did what you’re considering. I installed an Orion Smart 12-12/30 to replace the Blue Seas ACR between my lead acid starter battery and my 2 Battle Born LFP 100AH batteries wired in parallel. I also installed a BMV712 with Smart Shunt which is networked with the Victron Smart 100/30 isolated MPPT, running off 2 170W solar panels, also wired in parallel. I was advised by Battle Born to remove the ACR as it could not be adjusted to handle the voltage differences between the FLA and LFP batteries. The Orion DC-DC charger works like a charm and keeps the 70A ”dumb“ alternator from getting fried from excess voltage coming off the Battle Borns. It’s a good idea to know what your house loads are in AH so you can size the new LFP house bank to handle them.

Here’s a schematic of what I did. All positives are correctly fused, although these MRBFs are not shown in the schematic.

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Modifications Space

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Answer 1 · 2021-06-10T17:30:18Z

rob-crawford answered · Jun 10, 2021 at 05:30 PM

Thanks Randy - this is really helpful. Two quick questions -

(1) the current combiner plays an important role in isolating the battery banks when voltages drop, so if the combiner is pulled and replaced by the Orion DC-DC charger, would the Orion unit provide that same protection?

(2) I want to size the correct DC-DC charger, if I have a pair of 200Ah Lithiums as the house bank, is the 30A Orion charger enough?

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