Thanks Dave. I always simplerI can think of no reason to put LA and LFP batteries into the same bank. If this was really a good idea, he'd have competition or the big companies would be producing similar products. When I installed LFP in my boat, I did look at his black box and decided it certainly wasn't worth the money.
Most boats that have LFP house banks also have a LA battery for an emergency/start bank. Setting that system up is pretty simple it only requires a DC to DC charger and some cabling changes. A Victron 18a 12v DC to DC charger can be had through Amazon for about $160 USD.
The link below shows how to set up a simple and economical LFP bank. It does have a few limitations and doesn't take full advantage of LFP's charge acceptance rate, but it works and is considerably more affordable.
Easy LiFePo4 Conversion - Marine How To
Easy LiFePo4 Conversion Before reading this article please read the 101 article on Drop-In's: Drop-In Batteries Be An Educated Consumer Hardly a day goes by where we don't see or hearmarinehowto.com
The theory behind installing an FLA battery in paralllel with the LFP house bank is that it will protect the alternator in case the LFP bank disconnects unexpectedly. The FLA battery absorbs the potential voltage spike, saving the alternator diodes from damage.
The typical use of the DC to DC is to connect the start bank to the alternator directly, and then charge the lithium with the DC-DC. This setup does protect the alternator, but it limits your lithium charge rate to the size of the DC-DC (most commonly 50A). The alternative is to connect the lithium straight to the alternator. In that case a BMS shutdown could kill the alternator unless there is lead in parallel. But putting the lead in parallel creates new challenges like some of the ones the Bank Manager says it helps with. Instead of putting lead in parallel you could also properly configure the charging sources, and use an alternator regulator that can communicate with the BMS.
I've never tested it. I doubt the charger could absorb enough to be effective. If I recall, someone asked @Maine Sail once, and he said no.
So I guess your looking at an external regulator....or is the DC to DC converter basically the same thing?
The regulator controls the field current to the alternator. The higher the field current the higher the alternator's output. Some alternators have built in regulators, others use external regulators. The advantage to an external regulator is the ability to program the regulator to match the batteries charging profile and to adjust the alternator's output based on battery type, alternator temperature, engine speed and other variables.
Yes, you can do this and it may be the right solution for you. However, realistically you'll be limited to about 30a of charging to 300ah bank. The 30a limit is my guess because the Hitachi alternators ramp down the output to protect the alternator. If you motor a lot or frequently return to a marina and shore power you'd probably be OK depending on your power needs and consumptions. Adding 300 to 400 watts of solar would help extend the time between shore power charging.
Thanks Dave. That was my understanding that the Hitachi alternator produces approximately 50% of its rated output once it reaches operational temperature. I can foresee a Balmar 100 amp alternator with external regulation in the future.
Take a good look at the Arco Zeus Alternators and Regulators. About the same cost and much improved alternator control and a better alternator.
