MPPT controllers.....

[NotCook]

You could do what Misfits did, if your controller is programmable for either 12v or 24v output. My Hamilton Ferris MPPT controller has this capability, and, with the transfer switch, could charge either system. In addition, the MPPT controller charges the batteries through the proper stages of charge, and maintains a float charge. My boat's battery charger doesn't do this, so I generally leave it off, even when hooked up to shore power.

I do like this approach. The problem with putting two in series in parallel is that in almost any case, at least one of our panels will have shade from the mast or boom. We have one panel on the davits, one on the pilot house, and one on each side. Yet, to get 24V, obviously I will have to series in some combination.

I am still wondering if I can just add a second controller to charge each 24V bank individually as 12V batteries. Cables from the controller (12V) to each 12V battery, even while they are separately connected to the load in series as a 24V bank. That way, both individual batteries in the 24V bank get charged as individual 12V batteries. The second part of this is, can I actually connect two controllers in parallel to the same panels, each drawing what they can as available. Typically, the 12V house bank will not be constantly be drawn upon except when the fridge is running, other than the float on the bank. That would leave the bulk of the current to go to the other 12V controller which is servicing the individual 12V batteries in the 24V banks. No switching involved, no reprogramming involved, to service both voltages.

I don't know what I don't know...

 

[Bob J.]

I used the relatively new Victron MPPT controllers.
. The Victron controller includes bluetooth to a free app on your phone to monitor what's going on and adjust settings.

I originally was leaning towards a Victron controller but once it detects the battery voltage you do need to reprogram it if you want to use it for another battery voltage. Even with the bluetooth, smartphone app, just seemed like a PIA to me. That was one of the reasons I went with the Midnight Kid controller. With the transfer switch off & PV input off once I flip the transfer switch to whichever bank I want to charge, the controller detects the voltage & does it's thing. Plus it has a fairly easy to use menu screen which for me was another plus. You will need to wire something in series to charge a 24 volt bank with 12 volt panels.

 

[CarlN]

Misfits, I can see why that would be a pain with the Victron but, as you say, for the special case where you are trying to charge both 24v and 12v banks. For the OP who is apparently just using 12v banks this isn't a problem. I've loved the Victron bluetooth app as it tells me what's going on at the moment and also shows a history of the daily watts, maximum watts, and voltage and maximum voltage from each set of panels. It makes it very easy to figure out how shade and boat orientation is effecting your system. Especially when you compare multiple controllers. I also didn't have find a place to mount an external display or run wires to it.

 

[heritage]

I am still wondering if I can just add a second controller to charge each 24V bank individually as 12V batteries. Cables from the controller (12V) to each 12V battery, even while they are separately connected to the load in series as a 24V bank. That way, both individual batteries in the 24V bank get charged as individual 12V batteries.

I have read that the batteries can be charged with a 12v chargers while they are connected in a 24v bank. It is a common setup for 24v trolling motors. You have to use a charger for each 12v battery though. I ASSUME that two mppt controllers could be used instead of plugin chargers. This setup would need a total of three controllers for your two battery bank. Have you considered adding a 24v panel to your solar array? This would simplify things greatly.

 

[NotCook]

I have read that the batteries can be charged with a 12v chargers while they are connected in a 24v bank. It is a common setup for 24v trolling motors. You have to use a charger for each 12v battery though. I ASSUME that two mppt controllers could be used instead of plugin chargers. This setup would need a total of three controllers for your two battery bank. Have you considered adding a 24v panel to your solar array? This would simplify things greatly.

Really don’t have room, at least at this time, for yet another panel, and any one panel would be subject to periodic shade from mast, boom, etc.

I’m going to start drawing out a wiring diagram for multiple charge controllers to see what problems are created.