I have a solar charger on a vehicle which I need to protect:
Schematic is down there... The charger connects to the main battery, and the solar panel, but the manual specifically states that you MUST connect the battery 1st, THEN the panel, or the controller can be damaged.
The issue is that there is an external safety battery cutoff that allows the battery to be disconnected for maintenance - so someone could knock the cutoff and remove the battery without having disconnected the solar panel.
Now, it's easy enough to imagine putting relay in the solar panel line, but the question is how to control it - once the panel is connected & the sun's shining, the controller is feeding charge out to the battery so both sides of the cutoff will be getting volts, and for safety the battery side of the cutoff should really be isolated & dead when the switch is open as it likely means the cables are removed & dangling.
To clarify the situations we can experience are:
On the controller side of the cutoff we may be getting battery voltage coming out of the controller, or we may not if it's dark.
On the battery side of the cutoff, we may get full battery voltage (battery connected but cutoff open), or we may have a complete open circuit (battery removed).
We need to detect the cutoff being OPEN, NOT the absence of a battery
I'm looking for suggestions that are simple, low-power, and robust (automotive systems can have serious currents & transients, cutoff is rated to handle 100A). If it helps, there is a 2nd supply available (vehicle has two batteries) so the circuit can use some 12v power from elsewhere.
Thanks in advance!