A power pack for a power tool. The power pack includes an electric motor configured to drive a power tool. The power pack also includes a motor controller with a relay circuit communicating with the electric motor. The relay circuit has a switch that may be connected to a power supply, whereby the power supply powers the electric motor. The power pack also comprises non-transitory computer-readable storage media having computer-executable instructions for monitoring operation of the power pack. When executed by at least one processor, the computer-executable instructions cause the at least one processor to: monitor input data relating to operation of the power pack; determine, based at least in part on the input data, that operation of the power pack deviated from an ideal state; and, based on the determination of deviation, cause the switch to electrically disconnect the electric motor from the power supply.