Mundo wrote:It's a 48 VDC 20 AH battery, with a higher rated BMS. My guess is, a contactor/relay rated at 30 or 40 amps, with 48 volt signal/coil wires.
If you don't know the max currents (sustained, at least) that your system will draw, it's difficult to size your contactor correctly. You may not need one anywhere near as big as that, if your bike typically only draws 10A, for instance. Or if it draws 80A sustained all the time, you may need a much bigger one. Do you have a wattmeter or a multimeter with a high-current setting?
As DrkAngel posted, golf cart stuff will probably work.
You can also get keyswitches themselves that can handle the current, and skip the contactor entirely.
What I recommend, to keep wear to the contacts to a minimum, is adding a precharge circuit that you press a button or flip a switch, and it connects a precharge resistor across teh main contacts to first charge up the caps on your controller, before you turn the key. That way there isnt' any arcing across the cotnacts, which is what usually damages them. Without arcing, even a switch rated for less than the max peak currents you will draw may last for years.
You can also get a multi-position keyswitch, and use the first position for precharge. Turn key to that, wait a few seconds, then turn to "on", which either directly connects things or engages a contactor.
Magnetic coil types are easier to deal with, but the others could work for you too, if you can work out the mechanical activation for them.