Voltage switch

I have recently built 4 different Vell3man kits for fun, and every one of them works beautifully. For a complete novice, this is very exciting and encouraging. They are a FM radio receiver, a kitchen timer, a light sensitive switch and an infra red light barrier, I also have practical applications for each project.
What I really need now is a kit that can activate a switch at a given voltage, ie as a controller to divert power to a dump load to control battery charging.
I have a 48v, 2.2kw wind turbine that is controlled by a box that simply switches off the turbine when the batteries are full. I want to be able to divert the power to a series of heaters, so as not to waste the wind opportunity. I will need several such switches.
Many thanks, (fingers crossed)

Sorry, none of our kits are suited for this purpose
This requires a custom designed solution.