Solar charging of multiple banks - how?

[jdege]

I'm trying to design a solar charging system for my boat.

It has two 48V electric motors that draw a max of 80A, and two 48V 100Ah batteries.

It will have four 12V 100Ah batteries in parallel for the house bank.

It has, as of now, no solar installed. That I'll be dealing with this spring.

What I want is to be able to switch the solar from charging one bank to another.

I currently have three banks, two 48V and one 12V. I've considered wiring the two 48V in parallel so I'd have only one 48V bank, but no matter what I do I'll have at least two banks.

What I want is to be able to redirect the solar charging into whichever of the banks needs charging. It may be, for example, that I've not been running the movie for a few days, and I need to charge the house bank, of perhaps I've been motoring a lot.

I've seen 12V charge controllers, and 48V charge controllers, and I've seen one that can be configured for either.

How feasible would it be to install separate charge controllers for each bank, then switch the solar input between them?

Or would it make more sense to wire all the solar input to the charge controllers then switch the connections between the charge controllers and the batteries?

 

[42OhmsPA]

I would look into using DC-DC converters wired to the banks.
Dedicated 12V and 48V SCC for each bank. Parallel the 48 banks.
Use the converters to transfer power from 48V to 12V or 12V to 48V. Put a quality shunt on each pack for accurate SOC tracking.

I have no experience in the marine world but that's how I would go about it. Swapping wires/cables and reprogramming setting will get old quick.

 

[GXMnow]

I would recommend paralleling the two 48 volt banks. Setup the solar to keep that charged. Then use a DC to DC 48 volt to 12 volt charger to charge the 12 volt system from the 48 volt system.

The only real tricky part is making sure the DC to DC 12 volt charging system does not drag down the 48 volt system if there is not enough sun. If the DC to DC charger does not have this protection built in, you can add something like a low battery protect which will cut off the power to that charger when the 48 volt battery falls below a set level.

 

[yabert]

I've seen 12V charge controllers, and 48V charge controllers, and I've seen one that can be configured for either.

Many SCC can charge 12V and 48V.
So, of course I suggest as other a DC-DC from 48V to 12V, but on a boat it can be useful to be able to swap / disconnect few cables to charge the 12V.
Example in case the 48V battery or the DC-DC have problem you can still rely on the 12V for emergency.

 

[jdege]

I've seen people suggest using an MPPT controller as a DC->DC charger.

Any idea how well that works? Because it would give me the option of rewiring to charge the 12V bank at need.

(Once you get a cruising boat into the back of beyond, being able to rejigger things can be important.)

 

[yabert]

I've seen people suggest using an MPPT controller as a DC->DC charger.

Maybe, but with Victron Orion DC-DC starting at 70-110$, why don't get one more device?
That add one more choice when something go wrong.
I'm in the same boat than you with two 48V batteries + 12V and I look at the Orion 20A.
20A can seem low power, but over 24h it can transfer over 6 kWh from 48V to 12V

 

[GXMnow]

(Once you get a cruising boat into the back of beyond, being able to rejigger things can be important.)

If you are concerned about being able to manage an equipment failure at sea, then you should have a few redundant devices. I suggest splitting the solar onto a pair of charge controllers, but have each one large enough to take the whole array. If one fails, move all the panels to the working one. If the DC to DC fails, you can move one array to the 12 volts battery to put some charge there. The Victron 48 volt capable charge controller can all be changed to 12 volt with the app. And maybe even have a pair of the 48 to 12 volt DC chargers running in parallel, so if one fails, you are still working. You could also bring along a 12 to 48 volt CC CV boost converter that can be set up to push 10 amps from the 12 volt system to the 48 volt batteries. That way, if you have no sun, but the engine is turning the 12 volt alternator, you can still charge the 48 volt batteries.