Patent ID: 7817384

Claim:
A method of estimating tool motor temperature of a tool motor in a corded power tool, comprising: comparing a motor current value representing an estimate of what temperature the tool's motor will be after a given time period has elapsed, assuming constant current, to a temperature register value representing an estimate of the motor temperature at a present point in time, and updating the temperature register value based on the comparison so that the temperature register value equals the motor current value after the given time period has elapsed wherein upon tool startup, an initial temperature register value is determined by retrieving stored temperature data at the previous tool shutdown from a memory of a controller in the tool, the stored temperature data including a latest temperature register value at the last tool shutdown and a latest controller temperature at the last shutdown, after a given delay upon tool startup, determining controller temperature at startup, and comparing the determined controller temperature at startup to the stored controller temperature to determine the initial temperature register value.