I have a boat which currently has two standard, lead-acid batteries: starter and a deep cycle “house” bank. All on 12Volts.
Both of them are hooked-up to the alternator.
I’ve got a Mastervolt Powercharger 12/40-3, which chargers the two batteries individually from shore power; and a separate inverter.
I am contemplating a lithium upgrade for the “house” bank. The ideal requirements:
(R1) Alternator to be able to charge both batteries.
(R2) The shorepower to be able to charge both batteries.
(R3) In case of an emergency, lithium should be able to feed the starter.
(R4) Future solar upgrade should charge the lithium bank.
The current thinking is
Get the lithium bank for “house”, hook it up with a simple BMS and a smart shunt
Keep the starter battery attached to the alternator, and connect it to the lithium side with a dc-dc charger. This should help with the Alternator → Lithium charge path (R1)
a) Keep the current shorepower-charger that can charge two batteries separately (R2). Add an emergency switch that’d just put the lithium voltage to the starter (R3)
b) Switch out the existing charger+inverter combo to a victron charger-inverter (I think those can only have one output) and hook it up to the lithium side
Plus get a second DC-DC charger and wire it “backwards”, so that the starter can be charged from shorepower (R2) and that could also help with charging the starter in case of emergency (R3)
I wonder: does anyane have a good reference design for 2 batteries, alternator + shorepower setup?
Is it okay to wire up three DC-DC chergers (two parallel from Starter → House and one from House → Starter direction)?
We have a similar system. The alternator charges the start battery (agm). An Orion XS dc-dc converter senses “engine on” via remote switch and charges the house bank (LiFePO4, smart). The inverter/charger charges and draws from the house bank. MPPT solar charges the house bank. The house bank is monitored by a smartshunt. Charging of the start battery is by 1) alternator and 2) a separate Blue Smart IP65 5A charger, plugged into the inverter output and on a switch. The start battery requires very little charge so the Blue Smart charger is normally off except when on shore power. As you describe, we also have emergency switches to combine or isolate the battery banks. The system works very well, although I have noticed some small phantom draw on the start battery which seems to be coming from the Orion XS. We have also installed alternator protection, which provides some protection in the emergency use situation.
@tgsail1, thank you so much for describing your system!
It indeed makes a lot of sense!
Based on the literature I could find, I understand that having an AGM connected (starter bank) to the alternator is a good start, plus the DC-DC charger is also a good source of protection – and I was under the assumption that it’d be sufficient for me to.
However, you said you’ve added for some extra protection, I wonder if you could share details on what your though process was? What do you use for extra protection? I wonder if I should do the same too!
Related question: does anyone know if it’s safe to use the old charger (was built before Lithium; but can do IUoUo charging) for the first phase of the conversion?not
Hi- I added a Sterling Altprotect device, which just provides protection to the diodes in the event of an overvoltage. I did this because I have an externally regulated alternator with a remote sense wire. If the sense wire becomes disconnected the diodes in the alternator die. I probably do not need them. In answer to your other question: any charger with Constant Current/Constant Voltage capability will work if voltage and current are programmable and you are using LiFePO4 drop-in batteries with internal BMS.