I am not sure what a 'C' post is on a battery, but many '1-2-both-off' switches have a (common) post marked as such. And therefore I will mention that later.
If you check this link:
1/BOTH/2/OFF Switches Thoughts & Musings | SailboatOwners.com Forums
the first diagram is a most common (but not best) electrical
layout. The text shows the pitfalls of such configuration (BTW, that post courtesy of “MaineSail”).
Please read it, and if you abide by that (ie remembering when to use the 1-2-both-off’ switch) then all can be good.
The second diagram in that link shows a better setup, but you need to change the connections of the alternator
. But no new stuff needs to be purchased.
Now the solar controller. Many or most supply the regulated supply (output) on the positive side. That being the case:
Still using the 1st diagram (not sure if I can ethically copy that from a different user and different forum), one could connect the positive lead from the controllers to the ‘C’ (common) post of that switch. Not a good option in my opinion as it would mean:
- You need to leave the switch in the ‘1’ or 'both' position
- All the DC circuits are live/active while you are not at the boat
- If you were to put the switch in the 'off' or '2' position, then the solar controller is not connected to a battery, and some controllers may die in such condition.
Still using the diagram #1 in that link:
You can connect solar controllers to the ‘1’ post of the switch or to one of the positive terminals of the house batteries:
- You can turn the ‘1-2-both-off’ switch to 'off' when you are not on the boat
- Solar panels
will continue to charge the house battery
- You need to connect the essential equipment
like bilgepump to the same post '1' (and fuse it)
- all other DC equipment
will disconnected while you are away
- If your house battery bank has more than one battery, than all positive terminals will be connected with short thick wires, assuming all batteries are 12 Volt?
In short, as you said, it could be as simple as moving the solar controller output to the positive terminal of the house battery.
If things are not clear, let us know, there a lot of knowledge on this forum.