KlaassyC":22zxljfq said:
Our new to us 2018 C28 needs a new house bank and I want to use this opportunity to upgrade to lithium. Has anyone done this that is willing to share a diagram and any tips? I’m assuming it will make the most sense to use an inverter/charger and DC-DC chargers for the house bank, leaving the existing ABSO charger for the engine and thruster batteries?
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That is precisely how I did mine. I left the factory 20 amp battery charger for the engine and thruster bank. I installed a 60 amp battery charger dedicated to the LFP house bank. I have a 2000 watt KISAE inverter (factory). In fact, I can technically run the 20amp battery charger off the inverter via the LFP house bank to charge my engine and thruster bank.
Having an inverter/charger, you'll have to make sure it supports LFP. Also, the wattage of the inverter is important. Stay below 3000 watts. The inrush current on inverters can go sky high on amp draw on initial power up (it only does that for a few milliseconds, but it's enough to cause damage). Having an outboard gas engine, I am not able to run an inverter/charger. You may be able to upgrade your inverter charger and tie your alternator into LFP using an external voltage regulator as an option. That'd get you faster charging rates when running the engine. You have a much larger alternator than I do.
My setup is such that the Yamaha F300 has a 70 amp alternator. It outputs at most 50amps. With LFP, they say to size your DC to DC charger at 1/2 the size of your alternator. (35 amps for a 70amp alternator). This prevents the alternator from overheating when charging LFP. When I'm underway, the boat consumes about 15 amps (chart plotter, radar, sonar, etc...) which leaves me about 15-20 amps of charging. For a 320 ah battery, that's not a lot. Plus, I cruise at 25 knots so 2-4 hours and I'm done traveling. I get most of my LFP recharging from 400 watts of solar.
The below was on an RT27-OB, but would work on a C28 as well. The electrical systems are very similar. You could always install a pair of OrionTR 30amp DC to DC chargers in parallel also to boost your engine charging capabilities and take advantage of your larger alternator.
I've published everything about my upgrade, electrical schematics, parts lists, estimated cost, etc... on our website. It was a fair amount of work. I had to re-wire the entire cockpit on my boat. (Mainly because of how small the space is). Cost-wise, the most expensive part was the actual LFP battery itself. (labor would be the second most expensive part of the upgrade).
I have 320ah of LFP which equates out to 240ah usable. The boat came with 100ah usable (AGM) from the factory. I can run the microwave, coffee maker, and I can run my hot water heater. I also left a bunch of weight on the dock by upgrading to LFP. That single 320 ah battery is only 67 lbs. I also really like the fact that I only have a single house battery. That made cabling much cleaner as opposed to parallel cabling or bus bars of equal length for each battery.
Detailed writeup of LFP conversion
https://www.letsgochannelsurfing.com/lithium-techtalk
Electrical Schematic
https://www.letsgochannelsurfing.com/_files/ugd/b6c9c0_c62cce46057c4a50b1a7ddf8bc5b5cfc.pdf
Photos of the install
https://www.letsgochannelsurfing.com/lithium
YouTube video of my upgrade on my RT27-OB.
https://youtu.be/M7Z1lVW-t-Q
