Charging an Outboard Trolling Motor With Lithium and an Outboard Alternator?

Question:

I am the Assistant Manager at the Western Marine in Cape May. Many of my customers are getting large 36 volt trolling motors on their boats, using either single Li-ion battery or three Li-ion 12 volt batteries, totaling 100-200 Ah. They want to recharge this bank with their outboard engine. Can this be done? How? I can't find onboard chargers that run off OB alternators? Typical OB alternators don't have enough juice to do this efficiently on their own. Can you suggest a solution? Thanks.  - Todd

Answer:

For this setup we would recommend using a DC-DC charger from the OB motor battery to the Li-Ion bank.  12vDC to 36VDC may be difficult to acquire, Victron Orion models may be configurable for this purpose and each DC-DC will need to be sized to not overload the alternator.