I might be over thinking this but here goes
I currently have a solar system of 400w connected to two (in parallel) 110ah marine batteries through a solar controller. The panels are providing way more power than I need to keep the batteries charged and go to various loads.
I want to use that excess to put through a 12v immersion heater but only when there’s excess power being produced. My understanding of the controller is that when its load output hits a certain voltage, it will cut off. That would mean that not only the immersion but the fans, lights etc would also be affected.
I thought if I connected a second controller to my load output dedicated to the dump load, it would then only take the excess power.
So do I need a separate controller to stop all loads being affected?