500w hub motor convert to generator ? How do I wire it, Are the hall sensors needed.please help


You COULD get clever with the hall sensors, they'll tell you which way round each coil should be at any instant of rotation. Feed the hall signals to a bank of nice low on resistance mosfets, and make the mosfets switch like diodes - it'll be MUCH more efficient for a low voltage motor, since you won't be wasting 0.7 x output current Watts.
How many wires do you have ? I'd guess you have a polyphase AC coming out - an AC signal off each winding of the motor. Find the common wire, and wire a diode's anode  off each coil. The cathode of all the diodes is the output.