Homebuilt 48V controller ??

If you know enough electronics then the kits from Hosfelt and All Electronics do good for 48 volts. That is how I got my experience with PWM controllers to use as light dimmers and battery chargers and of course what they were designed for ~ Motors. The kits come designed for one transistor or one MOSFET but the final pass device can be paralleled if you use a set of FETS vs transistors.
Some of the cheaper kits require a separate power supply for driver board but again it can be modified also.
Rus