I have a 12 volt motor but a 17.5 volt battery. I was using a switching regulator to get the voltage down to 12 volts, and I was using a relay to turn the motor on and off. But now, having found that it is helpful to be able to vary the speed, I have substituted a Simple Motor Controller 24x12 for the relay. I am wondering, do I still need the switching regulator, or should I just connect the Motor Controller directly to the 17.5 volts and then run it at 60% max? Would it be more efficient with the switching regulator in line before the Motor Controller? Or is the Motor Controller going to be more efficient by itself?
You do not need the switching regulator, if you limit your maximum speed. Having it will most likely reduce the efficiency and the current capability.