Solar panels and controller for 48V and 12V systems on sailboat

[littleharbor]

The 'scale' of this task can vary widely from a 'small dingy' to a 'big yacht'...at some point there may be different possibilities of outcomes...guess that's where the math comes in...sorta like difference between a off-grid cabin vs off-grid palace...big difference...

Or like the difference between a Teardrop trailer and a class A diesel pusher

[neweclipse]

The 'scale' of this task can vary widely from a 'small dingy' to a 'big yacht'...at some point there may be different possibilities of outcomes...guess that's where the math comes in...sorta like difference between a off-grid cabin vs off-grid palace...big difference...

A quick way to 'ball park' math is by knowing how much petrol/fuel the solar is needing to replace is very usefull...

I'm no math wiz or engineer, but...3412 Btu equals 1kWh...where 1 gallon #2 fuel oil is equal to 138.690 Btu (@75% efficiency) for a base line...gasoline and diesel are some different.
So...using those numbers, 1 gallon #2 equals near 41 kWh...check me out, please...

[PNW_Steve]

Amanzi,

I am watching this thread with great interest. I have been kicking around the idea of a solar powered catamaran for a few years.

[neweclipse]

Some amount of 48v can be converted into a reasonable amount of 12v for the 12v needs.

As was hinted above, best to do some math for that 48 volt propulsion idea with solar panels...panels may need help of onboard generator to charge batteries or maybe chance it from a full charge to empty batteries from a prior stationary full recharge.

[PNPmacnab]

If you have one controller common positive and the other common negative, it will short out the switching. Using two with common negative, it is highly likely that they sense current on the negative side and the two shunts would be in parallel and not read current correctly. It is probably unlikely that a sailboat would have enough panels making that matter much. Most controllers have no idea what is going into a battery anyway. There are devices that will charge a 12V battery from a 48V bank.

[Xplode]

Be aware that some MPPT controllers have a common negative between the panel and battery. Others are switched. That would cause big problems.

Why would this cause problems? I'm assuming the various DC sources are probably common on the negative anyway?

[PNPmacnab]

Be aware that some MPPT controllers have a common negative between the panel and battery. Others are switched. That would cause big problems.

[Mike90250]

That requires 2 separate systems. And a whole bunch of panels to charge the 48V system.

[amanzi]

I have a 48 V battery bank consisting of 8 X 6V deep cycle golf cart batteries in series for an electric motor to drive the boat, and 12V battery bank consisting 4 X 6V in series and parallel deep cycle golf cart batteries for lights and instruments. Each battery is 225 amp hours. What solar panels and charger would you recommend and is it possible to use one set of panels and one controller for both the 48V and 12V bank, or do I need two independent panel systems.