I’m good at wiring and am a marine mechanic, I’m confused on what to use going forward so I’ll explain what I have , have a single outboard on boat , single 54 amp alternator, running to 2 battery set up start lead acid battery group 27, with a group 27 lead acid house battery, with a blue seas acr, I have bought a 320 ah house battery lithium with bms on board, I would like to retain my battery switch which allows me to combine batteries in the event of start battery fail. I understand that I need a dc to dc charger and cyrix battery combiner , but which one???
You will quickly find out that there are a lot of different ways you can build your new system. Understanding that you now have a system with two battery banks: “Starting” (group 27 x2) and a “House” (group 27 x 1). They are currently connected by a Blue Sea ACR and also a battery switch bypass around the ACR. You would like to add a Lithium battery in place of the lead acid group 27 currently as “House”.
Problem: If you replace the “House” battery with the Lithium and leave all wiring the same you risk burning up the alternator as soon as the ACR closes or battery switch and allows the lithium battery to max out the alternator.
Solution: Replace the ACR with a Victron Smart DC/DC Charger that is set for around 50% of alternator capacity. Alternators do not like to be pushed to capacity for very long. You might wire the third Group 27 formerly “House” over to the “Starting” group.
The difference between the DC/DC Charger and the Cyrix is that the Cyrix is like the ACR basically. The DC/DC Charger is completely different. It can take a 13.0V output from the alternator and step up its output to 14.2V Absorb voltage for your lithium battery. The charger will fully charge the battery using a complete multistep charge algorithm designed for the battery chemistry. (ORI121236140 Orion-Tr Smart 12/12-30A (360W) Non-isolated DC-DC charger)