36V18A controller is for the 36V250W/36V350W BBS01 motor; 

36V25A controller is for the 36V500W BBS02 motor;

48V25A controller is for the 48V500W and 48V750W BBS02 motor;

48V30A and 52V28A controller are for the BBSHD motor, according to your battery, please choose the suitable controller.