Making the switch to Lithium Batteries

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I've been thinking about switching from Lead-Acid batteries to Li-Ion for several years, but have been put off by the fact that I would have to change pretty much EVERY part of my charging and battery system. The benefits were very clear however, and I knew it was just matter of time. That 'time' came mid-season, when I noticed my group 29 110Ah Lead-Acid house battery was not holding a charge. Looking around locally, it was going to be about US$130 to replace. For LESS than that price, I could have 100Ah LiFePO4 battery (complete with an integrated Battery Monitoring System (BMS) delivered to my door.
The benefits are real. Over 80Ah (close to 100 in a pinch) of useable capacity (vs 45Ah), at 1/3 the weight. And 10x the number of charging cycles, and faster charging. This would be a slam-dunk for any boat owner, if that was the end of the story. But it's not. The trick is the the BMS, a 'computer' built into the battery that manages its charging. One of the things it can do is immediately turn off the battery terminals (stopping all power in or out) if it senses a potential issue. While the BMS is a god-send to Li-Ion batteries from a safety perspective, this ability to 'turn off' the battery will wreck your alternator if it happens while charging. With nowhere for the 40+ amps of current to go, blown diodes at the typical result. The solution is straightforward, but requires more parts, and parts swapped out. 

Best practice says that you leave your STARTER battery Lead-Acid, and only charge that with the alternator, and then charge the house bank from the starter battery with a DC-to-DC charger. This protects your alternator. The diagram looks like this:
The DC-DC charger I chose was the Renogy 12|12|40, a solid 40h charger, well regarding in the marine and RV space. It is lightweight and power efficient, meaning that half of it bulk is not made up of heat sinks or cooling fans.
That will charge the boat under AUX power. But our use-case says that we also need a very good shore power solution. and that means a new shore power charger, as my old one was not Li-Ion compatible. After some research, I chose the Victon 12|17 unit, which also has BT communications and a controlling app. When I first plugged it in, it asked to update the FW in the charger. Brave new world!
The last piece of the puzzle was my on-boat battery monitor. My trusty NASA Marine unit was working like a champ, but sadly did not support Li-Ion batteries. So back to shopping, where I ended up with anther Renogy product.
This unit has a big bright display, and a very useful readout. In addition, the display flashes to inverse video when charging, so you can spot that from a distance. All plugged in but not yet tidied up, the wiring looks like this. We're very happy with the results, and look forward to making a similar move on Northern Lights! 

PIC TO COME

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