New power finger file.

[Vinny]

(04-23-2018, 03:35 AM)toglhot Wrote: The unit works nicely, but curiously the 18 volt motor I sourced from an old cordless impact driver smokes badly when run on 18 volts. On 12 volts it runs ok, if a little hot.

The motor was more than likely designed to be controlled by PWM (pulse width modulation). The speed is controlled by varying the length of time the motor is receiving 18 volts and receiving 0 (duty cycle). This happens very fast so you don't notice it. You can hear the high pitch whine in some cordless drills. Anyway, the reason it doesn't smoke at 12 volts is because when running the drill at the same speed as you're getting with the 12 volts on your finger file, the duty cycle of the PWM's 18 volts averages to around 12 volts. A light dimmer operates much the same way, except with AC instead of DC. The brighter the light, the closer the duty cycle is to 100%.

Hope that made some sense.