Solar Charging Dual Bank 12v and 48v Lithium Batteries - Cape Dory 36 Refit Part 5

How to charge both 12-volt and 48-volt lithium batteries from 12-volt solar panels using transfer switches. Note: Because these transfer switches are rated for AC current only, over time with repeated DC switching under load the switches could become faulty. Once the switches are on they have no issue carrying the current, it's just that in theory, switching them repeatedly under load over time may damage them. My feeling is that because 200 watts of solar is a low arcing resistive load rather than the higher arcing inductive loads of say an electric motor, that there is no problem. But to ensure that does not happen, the transfer switches should only be switched when there is no solar output on them, such as at night or during daylight by placing a sheet over the solar panels temporarily. Another way to do it is to install an on/off switch on the solar input positive line before it reaches the transfer switch and then turn the input switch off temporarily to change the transfer switch.

Charging 12v house bank from 48v motor battery: 20 Amp Victron Energy Orion-Tr 48/12-20A DC-DC Isolated Converter $118. https://www.solar-electric.com/victro...

48v boost solar controller: Sunyima 48V 300w boost MPPT. I bought these on ebay for $31 each but they are now on Amazon for $40. We used two for two 200W panels:
https://www.amazon.com/SUNYIMA-Contro...

12v solar controller: Victron Energy SmartSolar MPPT 100V 30 amp 12/24-Volt Solar Charge Controller (Bluetooth) $128: https://www.amazon.com/SmartSolar-MPP...

Two transfer switches for solar charging 12v and 48v banks: Szliyands Universal Rotary Changeover Switch LW26-32, 32A, 3 Position, 8 Terminal $16 each. https://www.amazon.com/gp/product/B08...

We can be reached at atomvoyages.com. If you own a classic sailboat and want to share your experiences or have questions on fitting out, consider joining the Plastic Classic Forum at https://plasticclassicforum.com/forum/ I'm a moderator on the forum and answer questions there. James Baldwin