I have a portable mortor mixer that came with a on/off switch. My mixing time is consistantly 3 minutes long. I would like to know if it is possible to buy/make a toggle/rocker switch along with a timer that when the switch is thrown, the mixer will run for 3 minutes and then shut off and then the timer reset for the next mixing. This would help me from continously having to look at my watch while working durning batch mixes and help eliminate under/over mixing times. The material I am working with is a bit messy so a timer with a turn knob would not last long after it got coated with material off my hands. The motor on my mixer has a rating of 0.55kw, absorbed current 9.2A, 115 volts, and frequency of 60 Hz.
An alternative would be to use a time delay relay designed for industrial control systems, such as this 820 Series from Magnecraft. This relay could be set in 'inteval mode" and installed in series with an existing toggle switch (on the load side). Then you would just turn the mixer on, and the relay will limit the run time of the mixer to the programmed time. turninh the power switch off and on again would initiate a new cycle. Turning off the switch will immediately stop the cycle.
A darkroom timer would be ideal, but finding one that goes 3 minutes (rather than 1) and handles 1000W looks tricky. Alternatively, one of the 3-minute variety that can't switch that much power could be wired to a relay to do the job. But at that point, it isn't much more effort to get a microcontroller to do the timing and drive the relay. This last method is ideal because it lets you set the time pattern however you want, and you can change its behavior if you get new ideas.