How can I slow down an 120 volt ac motor it's a drift drive buffer. It is about 3500 Rpms I want it to be around 2500. Would a variable speed drive work? I'm in an electrical class but did not get that far.
note it says DC motor, it means AC motor.. the circuit can be adapted for 120V ac and is a good starting point.
An AC motor's speed is determined by the frequency of the commercial electrical supply, 60 hertz here in the US. If you had a 30 hertz source it would go half the speed. This is where a variable speed drive comes into play, commonly referred to as a VFD in industry (I happen to use them in my business). The VFD takes the commercial power input at 60 hertz and allows you to adjust the speed by changing the frequency (hertz) of the output which connects to the motor. VFDs have gotten much more reliable, cheaper, and smaller over the last 15 years or so. 2500 rpms will require around 42 hertz which should work for your motor. Some motors don't like going too low and we often limit the VFD output to 50% of max, in the US that would be 30 hertz on the output. The other option would be a gear box. There are many companies that specialize in that type of thing. A VFD is easier for existing installations because you can mount it anywhere near the motor (replacing the motor starter relay), while the gear box has to be attached to the output shaft of the motor.
