I have custom-build e-bike which is basically a motor, battery, controller and an LCD screen with 3 buttons. When I push ignition button, the LCD sets voltage on one of it's signal wires (blue) to 51 - 67.2V (BAT+, depending on battery capacity) which is then wired to the controller.
I would like to sense voltage on this ignition wire and switch on/off an external dc-dc converter (8-72V to 5V5A) in order to charge my phone while riding a bike. One downside is that I can't pull too much current on this signal wire - dc converter need to be wired directly to the battery by mosfet or something else.
After 3 minutes of idle, LCD automaticly turns e-bike off (0V on ignition wire) which is okay, i want to charge my phone only while riding.
I need a solution that uses no power when switched off in order to not drain the battery. I'm thinking of using a MOSFET as a switch where this ignition wire would be connected to the gate of MOSFET. As far as I understand I need a MOSFET with Vgs of at least 67.2V? Could anyone point me at a right mosfet? Wiring schematic and any tips on this would be great too. Thanks!