question

rob-crawford avatar image

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;

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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 smart solardc dc converters
1623278104680.png (76.4 KiB)
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2 Answers
randy-putnam avatar image
randy-putnam answered ·

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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rob-crawford avatar image
rob-crawford answered ·

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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