Electronic – Multiple charge controllers on the same solar panel

battery-chargingsolar cell

I have two 12v lead acid batteries on my boat. One at the front for the trolling motor (~80 AH) and 2 smaller batteries in parallel at the rear for electronics (~30-35 AH combined).

I want to put a solar panel on my garage, so I can hook the batteries up when I get back from the lake to recharge them and to keep them maintained. I only need a 30 or 50 watt panel to charge both battery banks, since I never use full capacity and usually have at least couple days between trips. Instead of buying 2 smaller panels, one for each battery bank, I was thinking about hooking up 2 charge controllers to the same solar panel.

The solar panel disconnect switch is required because the batteries should be connected to the charge controllers before the solar panel is connected. On my boat, I would add DC plugs for both batteries to connect the charge controllers.

I think this will work fine, but I have done a lot of searching and could not find any information about connecting multiple charge controllers to the same solar panel. I am aware they make dual battery charge controllers, but they don't look any better than the $10 units you can find on Amazon and they are more than double the price.


simulate this circuit – Schematic created using CircuitLab

Best Answer

Should work. Cheap charge controllers are a bang bang MOSFET switch, so either the battery is straight on the solar cell, or not. MPPT controllers have a switch mode buck converter; two of them on one panel will get very confused.

Once the battery is full, the charge controller switch will be mostly off, so the other charge controller can use the solar cell.

The danger might be that if both batteries are low, both controllers will come on together, shorting two batteries together and damaging the controllers. You could check for diodes or add them. They must go before the controllers, not between the controller and the battery, as it needs to sense the battery voltage.

The open questions are 1) are there already diodes in the charge controller, and 2) what does the controller do when the solar voltage collapses to ~14V (when the other one shorts the panel to the battery). It might panic and not charge.
It's worth asking the supplier about both of these, I'm sure they've had these questions before